Back when dinosaurs stomped the Earth, dinky mammals scurried about in their shadows. The little furballs, hiding out in underground burrows, provided a fresh niche for a novel reptile: the snake. Skinny snakes could squeeze into the homes of mammals and gobble them up.

At least, that's how the dawn of snakes is imagined by Marc Tollis, an evolutionary biologist at Northern Arizona University in Flagstaff. No one knows for sure. Like the creatures themselves, the snake fossil record is long and thin, leaving gaps in snaky history. Major questions, such as where they got their start and who their closest relatives are, remain unanswered.

Today, new fossils and modern techniques are updating the story of snakes. Starting about 125 million years ago, snakes used their flexible body plans to diversify like crazy, conquering regions that now make up six continents, plus the Indian and Pacific Oceans — and Tollis would not be surprised to find snake fossils in once-balmy Antarctica, either.

There are serpents slithering across the land, burrowing into the soil, swimming in the sea and gliding between trees, even catching rides on trains and, yes, planes. There are itty-bitty threadsnakes just a few inches long and thin as spaghetti, and there are pythons that exceed 20 feet. There are snakes that chase their prey and snakes that lie in wait to ambush it, snakes that strangle their meals and others that immobilize their dinner with venom. Snakes that lay eggs, snakes that bear live young, snakes that can reproduce without males.

It's an impressive smorgasbord of abilities for what is, essentially, a freaky offshoot on the lizard family tree. Serpents are basically predatory tubes, Tollis notes. They can't walk or chew their food. These seem like seriously limiting factors.

"Despite that, snakes are some of the most successful animals," marvels Tollis, who coauthored an overview of early snake and lizard evolution in the 2025 Annual Review of Ecology, Evolution, and Systematics. "They definitely have superpowers that we would normally associate with the fantastic."

By sea, by land, or below?

There are more than 4,000 described living species of snakes, accounting for about one-third of the larger lizard group, and probably hundreds more awaiting official discovery, says Alex Pyron, an evolutionary biologist at George Washington University in Washington, DC. Scientists estimate that the ancestors of this wildly diverse group emerged around 160 million years ago, but they haven't figured out what the first snakes were like — land snakes, sea snakes, perhaps underground snakes?

These mysterious, ancestral snakes should sit at the very base of the snake family tree, but their fossils haven't been found. The oldest snake fossils known come from a variety of environments, making it hard to determine which kind of habitat snakes wriggled out of, says Tiago Simões, a coauthor on the Annual Review  paper and an evolutionary biologist at Princeton University in New Jersey.

One longstanding hypothesis is that snakes got their start underground. The original idea was based, in part, on the barely-there eyes of the blind snakes that are the lowest branch on the family tree of living snakes. But blind snakes are quite specialized for the anthills and termite mounds they inhabit, says Catie Strong, a vertebrate paleontologist and graduate student at the Harvard Museum of Comparative Zoology in Cambridge, Massachusetts.

They have weird, alien-looking skulls fit for their subterranean environment and insectivore diet. For example, Strong says, a "pronounced underbite" helps keep dirt out of their mouths. While training with vertebrate paleontologist and evolutionary biologist Michael Caldwell at the University of Alberta in Edmonton, Canada, Strong concluded, as have other researchers, that these hyperspecialized critters can't correspond to the root of the snake family tree.

In the late 20th century, evidence supporting a possible marine origin floated up. Scientists described early snakes that lived nearly 100 million years ago in the Middle East, when that land was underwater. Caldwell and colleagues also linked the snake clan to mosasaurs, extinct aquatic reptiles, raising the possibility that snakes emerged in the water. But favor for that hypothesis has sunk: There are other snakes that predate those aquatic snakes and were clearly terrestrial, says Simões. So the current consensus is that the Middle Eastern swimmers didn’t spring from the water but dived into it from land.

Modern-day Patagonia has yielded a trove of additional snake fossils, such as Najash rionegrina, dated to about 95 million years ago, and Dinilysia patagonica, from about 80 million years ago, when that environment was desertlike. But were these South American serpents on the ground, or under it? Dinilysia probably lived aboveground, but the situation with Najash is trickier, says Simões.

Najash has skull and spinal features that, to its discoverers, suggested it spent at least some time underground. But both of these Patagonia species were "big-bodied snakes," adds Caldwell, similar to modern-day pythons. Like pythons, they might have hid out underground, but hunted on the surface, he speculates.

Additional evidence for a mixed dry land/underground origin comes from predictions about early snakes' brains. Scientists used 3D X-ray imaging to analyze the braincase — the part of the skull protecting the brain — of nearly 60 snakes and lizards, plus a few snake fossils. From those inner contours, they could infer the shape of the brain. The researchers identified burrower brain anatomy: Diggers usually possess, for example, a small, flattened, triangular cerebellum, a brain section involved in movement. When the researchers used their data to predict the ancestral snake brain shape, they wound up with some burrower-like features, including that little cerebellum, but other features inconsistent with underground living.

Bringing all the evidence together, Strong subscribes to a theory that snakes evolved on land, maybe in a sandy environment like the one Dinilysia and Najash inhabited. This, she suspects, also happened to set them up to navigate underground on occasion.

A better way to slither

Another major event in snake evolution was, of course, the shedding of their legs. This is not as innovative as it might seem; among lizard-kind, several long, skinny groups have kicked their legs to the curb. When one is crawling underground or moving through grass, limbs are literally "a drag," says Daniela Garcia Cobos, an evolutionary biologist and graduate student at the American Museum of Natural History in New York City. Snakes do, however, seem to have been among the first lizards to master this streamlined shape in a variety of different types of habitats, which might underlie their success with it.

Pyron estimates this change happened between 150 million and 125 million years ago, but scientists haven’t been able to pin down exactly when or where. The known fossil snakes had hind limbs but not forelimbs, though Dinilysia’s status is uncertain because there hasn't been good evidence of pelvic region preservation in those fossils. At some earlier point, there must have been a four-legged snake ancestor, but this missing link has been elusive. One candidate was reported in 2015, but Caldwell and collaborators showed it was just a lizard.

Then came Breugnathair elgolensis, a four-legged Jurassic fossil found in Scotland and described in Nature in 2025. "If you saw it in the street, walking across the road, you’d think it was just an iguana or ordinary lizard," says Susan E. Evans, a paleontologist at University College London, who described the specimen with colleagues.

But B. elgolensis's jaw does have some snaky features, like the shape of its teeth. Caldwell, who wasn't part of the team that described it, thinks it's a snake. "It's got all the right skull features," he says.

Evans isn't so certain, an opinion evident in the name she chose: Breugnathair derives from Gaelic for "false snake." When Evans and colleagues tried to place it in the reptile family tree, the results were wishy-washy. It might be a snake ancestor, she concedes, or it could be a lizard that independently evolved snakelike features but left no living descendants.

Heady changes

What distinguished snakes from all other legless lizards were the other changes they made, says Pyron. To investigate further innovations, Pyron and collaborators embarked on a massive reptile census, which they published in Science in 2024. They measured the skulls of thousands of snakes and lizards. They examined the stomach contents of museum specimens and pored over written dietary records. They amassed genetic data — not the whole genome, but 5,400 specific genes — from more than 1,000 snake and lizard species.

When they lined up those features, snakes stood out. About 125 million years ago, the group underwent sudden and significant changes to their skulls, diets and spines that would position them to diversify and spread.

Snakes' biggest claim to evolutionary fame is their weirdly flexible craniums, made of bony pieces connected by soft tissue; Caldwell thinks this key alteration might have happened even before they gave up their legs. En route to those piecework noggins, snakes first changed up their braincase. In most lizards, this looks like a sandwich: bone on top, bone on the bottom, brain within and open on the sides. But in snakes, it's more like a wrap, a bony tube that's only open toward the face and spine. Protecting the brain that way meant snakes were free to let the rest of the skull's bones move about. And boy, did they.

Those skull changes enabled new diets with the evolution of the serpentine jaw. While jaw anatomy varies within the group, in many snakes, the lower and upper parts are connected by stretchy ligaments, enabling a wide gape. The two sides of the lower jaw can splay apart, further expanding the snake's maw. The palate at the top of the mouth has right and left parts that move independently to convey food throatward. That's how a python can swallow a pig. Indeed, the Science team found that snakes, as a clan, can eat pretty much anything that moves. There are snakes that nosh on gooey slugs and armored snails, slippery eels and even other serpents.

And around the same time, snakes grew longer, adding hundreds of vertebrae between their necks and nether regions. "Being elongate allows you to locomote more quickly and efficiently," says Caldwell. Extra belly flesh supplies more surface area to push along the ground or climb tree trunks. For aquatic snakes, increased body length enables more efficient weaving back and forth.

In sum, these changes to body, head and diet meant the evolving serpents were flexible not just in form, but also in lifestyle. Snakes adapt rapidly to new environments, says Frank Burbrink, curator of herpetology at the American Museum of Natural History and a coauthor of the Annual Review  article. In other words, these evolutionary superstars were primed to make the most of any habitat they slithered into.

Making up for absent fossils

The fragmented skulls and the body length that were so beneficial for snakes' spread create a headache for paleontologists: Dead snakes go to pieces, making complete fossils scarce and leaving many questions unanswered. For example, researchers know serpents are related to groups containing iguanas and Komodo dragons, as well as possibly those mosasaurs, but it's not certain which are their closest cousins. Knowing that would help to predict what snake ancestors should look like, says Evans.

When fossils falter, genetics can come to the rescue. The more dissimilar the genes from different animals, the longer it's been since they went their separate ways as species. Already, genetic analyses have forced a reshuffling of the lizard family tree; trees based on body shape alone turned out to be "totally wrong," says Pyron.

Genes have also illuminated how snake bodies build some of their special features. The lack of legs is linked to lost function in a limb-promoting sequence called ZRS. And scientists recently reported that snakes lack the gene encoding the "hunger hormone" ghrelin. This might make it easier for them to endure long fasts; some snakes can go for a year or more between repasts.

Burbrink, Pyron and Simões are now sequencing whole genomes of more than 100 snakes and lizards, which will double the number of high-quality genomes available. With that plus additional data on living and fossil reptiles, they expect to build better family trees and further investigate the genes behind a snake's sinuous shape.

Still, Evans says, scientists really need more fossils to fill in the twists and turns in the serpents’ tale.

As paleontologists keep digging, Burbrink counsels us to take a moment to marvel the next time we come across a garter snake or other modern wriggler: "You're looking at the culmination of more than 100 million years of evolution."

This article originally appeared in Knowable Magazine, a nonprofit publication dedicated to making scientific knowledge accessible to all. Sign up for Knowable Magazine’ snewsletter.

Editor's note: This story was updated at 7:35 p.m. ET on July 27 to change a word in the strapline from poisonous to venomous. 

How much do you know about snakes? Test your knowledge with our snake quiz!

Cannibalism might seem like a rare and unnatural occurrence, but the behavior has arisen in several snake lineages throughout evolutionary history, often triggered by environmental stressors, scientists theorize.

When researchers reviewed 500 reports of cannibalistic behavior across snake species, they found that cannibalism has evolved independently at least 11 times, according to a study published Nov. 2, 2025, in the journal Biological Reviews.

These cannibalistic behaviors occur in diverse contexts, but overall, cannibalism is common and seems to emerge repeatedly because it's beneficial to snakes in situations where they need to make opportunistic dietary choices, the researchers suggest.

"For us humans, we don't think of cannibalism as something common –– it's something weird and disgusting," Bruna Falcão, lead author of the study and a graduate student in biology at the University of São Paulo, told Live Science. "But for snakes, it's good for them; it's good for their ecological fitness. … It's strategic."

Evolutionary advantages of cannibalism

Some of the best-known examples of cannibalism in nature are seen in spiders and praying mantises during mating, as it may be beneficial for females to eat their mates. "Cannibalism is widespread throughout the animal kingdom," Xavier Glaudas, a biologist and National Geographic Explorer who was not involved with the study, told Live Science.

Although scientists previously considered the behavior maladaptive –– meaning it's not beneficial for a species overall –– more and more studies reporting cannibalism in animals hypothesize reasons for the evolution of the behavior. For example, it could help parents control brood size, or it might arise as a response to limited resource availability, a form of population control, or an opportunistic predation choice.

Cannibalistic behavior in snakes has typically been recounted in brief and isolated reports, Glaudas said. For example, his research team described male Montpellier snakes (Malpolon monspessulanus) feeding on female snakes in France — a behavior thought to be driven by limited food resources, especially during times of scarcity outside the mating season. (It would be considered unusual for males to eat females during the mating season, as this would reduce mating opportunities.)

In addition to being widespread in snakes, cannibalism has evolved independently across different snake lineages and regions, according to the study, which combined numerous reports to explain the behavior.

The research team gathered 503 cases of reported cannibalism across 207 snake species. The reports spanned a wide range of snake groups, as well as all continents where snakes live, including reports of snakes both in the wild and in captivity.

"None of us expected that … snakes could be so cannibalistic, and no one was talking about it," Falcão said. "The more we were searching, the more cases we found."

Cannibalism was most common in the Colubridae, Viperidae and Elapidae families, the team found. Colubridae is the biggest family of snakes and made up 29% of all reports. Because this family is not typically known to prey on snakes, however, the authors proposed that most cases of cannibalism in this group may be connected to stressors such as a lack of other food sources. Members of the Viperidae family, which includes vipers, made up 21% of all cannibalism reports. But these were mostly cases in captivity, the researchers noted, so captivity-related stressors, like confinement to small spaces with limited food, may have resulted in cannibalism.

Elapidae, the snake family that includes cobras, accounted for about 19% of the cannibalism reports. This wasn't very surprising, the researchers said, because cobras are known to prey on other snakes in the wild.

Almost half of the cannibal snake species have generalist diets, according to the study, and the researchers linked this dietary flexibility to cannibalistic behavior when necessary. However, Glaudas suggested this connection may not be clear, since the researchers defined only 47.7% of the cannibal snake species as generalist; evidence for the relationship would be stronger if the percentage were higher, he said.

"In regard to the idea that cannibalism could be more common in generalist species, I am a bit more skeptical about the data presented," Glaudas said.

Cannibalistic behavior does seem to be correlated with jaw structure, so whether a snake has jaws that can open wide enough to consume another snake is a key factor; there were no reports of cannibalism in snake species without this ability.

When the researchers analyzed cannibalistic behavior across snakes' evolutionary history, they concluded that the behavior evolved independently at least 11 times throughout the snake evolutionary tree.

Because most reports of cannibalism in snakes are anecdotal, Glaudas said, the study provides a useful overview. This is a "welcome study that allows us to get a better understanding of the correlates of cannibalism in snakes," Glaudas said.

Snakes form a highly successful branch of the evolutionary tree. They are found on all continents except Antarctica and have adapted to most ecological niches, the study authors noted. Because cannibalistic behavior appears in many different types of snakes throughout the world, Falcão said, it might reflect their ability to adapt opportunistically to their circumstances. "It's really surprising for [cannibalism] to evolve independently 11 times in snake lineages," she noted.

The review could not encapsulate all reports of cannibalism in snakes — many are in less-accessible, older books and archives — so there's likely much more to discover on the topic, Falcão said.

Saltwater crocodiles used to occupy a massive range that stretched across the Indian Ocean to the Seychelles, new DNA research confirms.

The now-extinct population of crocodiles in the Seychelles, an archipelago in the western Indian Ocean, was not a group of Nile crocodiles (Crocodylus niloticus), nor was it a separate species. Instead, it was likely the westernmost population of saltwater crocodiles (Crocodylus porosus), which today live in India, Southeast Asia, Australia and islands across the Western Pacific, researchers reported Jan. 28 in the journal Royal Society Open Science.

"The founders of the Seychelles population must have drifted at least 3,000 kilometers [1,864 miles] across the Indian Ocean to reach the remote archipelago, perhaps even much further," study co-author Frank Glaw, a reptile expert at the Bavarian State Collections of Natural History, said in a statement.

The Seychelles used to be home to a large population of crocodiles, according to expedition notes from more than 250 years ago. But when human settlers arrived in the late 18th century, they wiped out all of the crocodiles on the islands. The remains of a few specimens were kept in museums in the Seychelles, London and Paris.

Initially, Western scientists thought the Seychelles crocodiles were part of a population of Nile crocodiles that had migrated from Africa. But in 1994, researchers reclassified the preserved remains as saltwater crocodiles based on their physical traits.

In the new study, a different team of scientists confirmed that conclusion using genetic material. They collected mitochondrial DNA from the skulls and teeth of several older museum specimens of various crocodile species and then compared that DNA with tissue samples from modern museum specimens and living crocodiles.

The genetic markers of the Seychelles crocodiles matched closely with those of the saltwater crocodiles, the team found. That suggests that saltwater crocodiles' range stretched over 7,500 miles (12,000 km) from east to west before the Seychelles population was exterminated.

"The genetic patterns suggest that saltwater crocodile populations remained connected over long periods and across great distances, pointing to the high mobility of this species," study co-author Stefanie Agne, an evolutionary biologist at the University of Potsdam in Germany, said in the statement.

To spread as far west as the Seychelles, C. porosus would have had to cross thousands of miles of ocean. But the crocodiles are adapted to life at sea, sporting special salt glands on their tongues that let them expel excess salt. That adaptation could have helped the animals spread widely across the Indo-Pacific region and limited further speciation, the researchers wrote in the study.

But future work could still uncover differences among groups of saltwater crocodiles. Mitochondrial DNA is inherited only from the mother, and it might not capture subtle genetic differences driven by male crocodiles. Future studies using DNA from the nuclei of crocodile cells could help unpack any regional differences among populations, the researchers wrote.

In 2024, scientists announced the discovery of a newfound anaconda species in the Ecuadorian Amazon. Now, in a new nature series, filmmakers have released nail-biting, never-before-seen footage of the moment they encountered the snake in the wild.

The footage transports viewers to the Baihuaeri Waorani Territory in the Amazon rainforest, where researchers were sampling anacondas in 2022 for a snake genetics study. In the video, venom expert Bryan Fry and actor Will Smith travel by boat with Indigenous Waorani guides along the banks of a murky river. In a small clearing, the group spots a gigantic anaconda, which the guides manage to immobilize so that Fry and Smith can take a piece of its scales.

The anaconda in the footage — which features in an episode of National Geographic's upcoming "Pole to Pole with Will Smith" docuseries — is a female measuring 16 to 17 feet (4.9 to 5.2 meters) long, Fry estimates in the show. There is a danger she might bite, says one of the Waorani guides who helps pin down the snake, even if green anacondas aren't venomous. Anacondas are constrictors, meaning they kill prey by wrapping their bodies tightly around it, suffocating the animal before swallowing it whole.

The scale sample and others taken in 2022 revealed that green anacondas, which were previously thought to all belong to one species, actually form two separate species: Eunectes murinus, the already-identified southern green anaconda, and Eunectes akayima, the newfound northern green anaconda.

"Finding a new species is so often not a case of actively searching but rather having rigorous scientific process in place so that serendipity can strike," Fry, who is a professor of toxicology at The University of Queensland in Australia, told Live Science in an email. "The research into the genetics of the iconic green anaconda is textbook in this regard."

Genetic analyses indicate that E. murinus and E. akayima diverged 10 million years ago. Since then, northern and southern green anacondas have accumulated thousands of genetic differences adding up to a whopping 5.5% of their total DNA. By comparison, the level of mismatch between human and ape DNA is about 2%.

As its name suggests, the northern green anaconda inhabits the Amazon's northern basin, which includes parts of Ecuador, Colombia, Venezuela, Trinidad, Guyana, Suriname and French Guiana. The southern green anaconda, on the other hand, is found in the Amazon's southern basin, which stretches across Brazil from Peru and Bolivia to French Guiana. Both species live in wetlands and rivers, spending most of their time submerged in water. Their olive-green coloring blends into their surroundings, which helps green anacondas ambush large prey such as capybaras (Hydrochoerus hydrochaeris), caimans and deer.

Green anacondas are the world's heaviest snakes, with some specimens weighing more than 550 pounds (250 kilograms) and exceeding 12 inches (30 centimeters) in girth. Female northern green anacondas grow the largest and heaviest, while their male counterparts have more slender bodies. This means female and male northern green anacondas hunt different prey and occupy different positions in the food chain, Fry said.

"Females and males live in the same environment, but they feed differently," he said.

The northern green anaconda is the fifth described anaconda species in the world — and there may be more hiding out there, Fry told Live Science. "Despite anacondas having a state of fame exceeding that of any other reptile, they are really poorly known," he said.

Knowledge of the northern green anaconda's existence is important in and of itself, but the difference in male and female diets could also give clues about the health of the ecosystem — and the people who live in it, Fry said. Female northern green anacondas feed lower in the food chain than males do, preying on animals such as deer. The males eat more predatory fish and caimans, meaning they accumulate more toxins leftover in the environment from events like oil spills than females do, he said.

Male northern green anacondas' diet resembles that of humans living in the Amazon. Therefore, the concentration of toxins in these anacondas provides an estimate of the pollution that people are exposed to — and that pollution is high, Fry said.

"The concentrations of the heavy metals cadmium and lead, potent endocrine disruptors that are the signature of oil spills, were over 1000 percent higher in males than females," he said. "That is not a subtle difference. That is a warning flare."

In light of these findings, Fry is developing a wild food guide for the Waorani. "Recommendations will include pregnant women and young children avoiding top-level predators likely to carry higher contaminant loads, such as arapaima and arowana [two types of predatory freshwater fish]," he said.

"Pole to Pole with Will Smith" premieres Jan. 13 on National Geographic, and Jan. 14 on Disney+ and Hulu.

How to watch "Pole to Pole with Will Smith" in the U.S.

"Pole to Pole with Will Smith" premieres in the U.S. on National Geographic and will be available to stream on Disney+.

The first two episodes will air from 9 p.m. ET / 6 p.m. PT on Tuesday Jan. 13 on TV. Then, on Jan. 14, all seven episodes will be available to stream in one go on Disney+.

How to watch "Pole to Pole with Will Smith" in the U.K.

"Pole to Pole with Will Smith" will also air on the National Geographic TV channel and the Disney+ streaming platform in the U.K.

The premiere is a day later than the U.S. release, landing on Jan. 14 at 8 p.m. GMT. All seven episodes will be available to stream on Disney+ for U.K. subscribers from Jan. 14.

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It's a long-held idea that turtles can tuck their heads into their shells when threatened. But is it true? And is this protective trick why turtles the world over have shells today?

The answer is that some types of turtles can, and others can't, experts told Live Science. And even though shells can be protective for some of these reptiles, fossil evidence suggests that shells evolved for entirely different reasons.

Tortoises are one type of turtle that can tuck their heads into their shells. This terrestrial subgroup of turtles emerged 50 million years ago, Tyler Lyson, senior curator of vertebrate paleontology at the Denver Museum of Nature and Science, told Live Science. They typically move slowly, so they rely on their shells to protect them from predators. Most tortoises can draw their heads into their shells, which typically also have a domed shape with more space inside to make that possible.

Several terrestrial turtle species, which split their time between land and water, can do the same.

"Turtles have two ways of tucking the head in," Jason Head, a professor of vertebrate evolution and ecology at the University of Cambridge, told Live Science. "We have what are called the side-neck turtles. They have long necks, and they literally fold the head and neck to the side over one of their arms. And then there are the snake-neck or S-neck turtles, which put a loop into the neck, and can actually pull the neck into the shoulder girdle."

One example is the eastern box turtle (Terrapene carolina carolina), whose bottom shell, known as a plastron, is fitted with a hinge that even allows it to completely close up the shell.

But sea turtles are one group of turtles that cannot pull their heads into their shells. Sea turtles have much sleeker, lighter shells that contain no space for them to tuck their heads inside. "This is to lighten the load," Head said, and it allows sea turtles to swim faster to escape predators.

How turtle shells evolved

So, how did some turtles develop this lifesaving trick? To find out, we need to explore how turtle shells evolved, which takes us back almost 300 million years in the fossil record.

"The turtle shell is a complicated structure. It's made up of over 50 bones," Lyson said. "Bone" is the key word, because fossils reveal that turtle shells are part of their skeletons. And while the modern turtle's shell looks like a solid unit, it's actually made up of two skeletal features that evolved separately.

"The first thing we see in the evolution of the turtle shell is the broadening of the ribs, and we see that in Eunotosaurus africanus," a creature that lived in southern Africa 260 million years ago, before dinosaurs roamed Earth, Lyson told Live Science. Lyson first described Eunotosaurus' contribution to turtle evolution in a 2013 study. Researchers think that these creatures spent time burrowing underground to escape the heat and that the development of wider ribs supported more muscle mass that enabled them to do that.

Then, in Germany, the 2015 discovery of a 240 million-year-old fossil called Pappochelys showed a shell-less animal with wider upper ribs paired with thicker belly ribs — known as "gastralia" — on its underside. By 220 million years ago, an aquatic animal called Odontochelys found in China had developed a fully unified belly plate — the plastron — partly from the expanding gastralia.

"Myself and others think that the evolution of the plastron was a ballast for basically going deeper into the water column," Lyson explained. It's also possible the plastron developed to protect turtles from predators swimming below, he noted.

The first evidence of a fully formed turtle shell comes from 210 million years ago, in the shape of a fossilized creature called Proganochelys, whose thick upper ribs had fused together with dermal bone, forming a closed carapace, attached to a lower plastron. The opening for the turtle's head was formed from shoulder bones that connected the top and bottom of its shell, Lyson explained.

Most evidence suggests that these reptilian creatures, called Pantestudines, ultimately led to modern-day turtles. However, Head noted that similar features — like widened, overlapping ribs — also developed in other animals millions of years ago, including some thought to be more closely related to mammals.

"It's an active area of research, with new discoveries coming all the time," Head said.

The shells of these turtle ancestors developed as a response to varied evolutionary pressures, but today, the turtle's shell is used primarily for self-defense, Lyson noted. "The modern-day function isn't necessarily related to how that feature arose," he said. "It wasn't until you got the full advent of the shell that it was for protection."

The turtle's resilient shell has seen these creatures through almost 300 million years of history, and Lyson thinks it's one reason they've managed to survive three of Earth's five mass extinctions.

"We see the fossil record, and we can see the line in the sand where dinosaurs and lots of other things go extinct," Lyson said. "And we see turtles marching right across that line."

Evolution quiz: Can you naturally select the correct answers?

Anacondas have been giant for millions of years, a new study finds.

The enormous snakes' average body size has remained constant since they first appeared in the fossil record about 12.4 million years ago, during the Middle Miocene (16 million to 11.6 million years ago), researchers revealed in a new study published Monday (Dec. 1) in the Journal of Vertebrate Paleontology.

During the Middle and Upper Miocene (12.4 million to 5.3 million years ago), warm temperatures, expansive wetlands and abundant food enabled many animal species to grow much larger than their modern relatives. But few of these giant animals have survived to the present day.

"Other species like giant crocodiles and giant turtles have gone extinct since the Miocene, probably due to cooling global temperatures and shrinking habitats," study co-author Andrés Alfonso-Rojas, a vertebrate paleontologist at the University of Cambridge, said in a statement. "But the giant anacondas have survived — they are super-resilient."

Anacondas make up a group of constricting snakes that today includes the heaviest snake species in the world. Modern anacondas average 13 to 16 feet (4 to 5 meters) in length, though the largest can reach up to 23 feet (7 m). Scientists weren't sure whether anacondas had been even larger during the Miocene, or whether they had been the same size and retained their massive size into the present day.

To estimate how big ancient anacondas might have been, Alfonso-Rojas and his colleagues measured 183 fossilized anaconda vertebrae from at least 32 individual snakes collected in Venezuela. They also used a technique called ancestral state reconstruction to predict the body lengths of ancient anacondas from characteristics of related snakes.

Based on these calculations, the team found that anacondas averaged about 17 feet (5.2 m) long when they first appeared during the Miocene 12 million years ago — roughly the same length as modern anacondas.

"This is a surprising result because we expected to find the ancient anacondas were seven or eight meters [23 to 26 feet] long," Alfonso-Rojas said in the statement. "But we don't have any evidence of a larger snake from the Miocene when global temperatures were warmer."

It's still unclear why anacondas have not become smaller over time.

Although warm weather and abundant wetlands may have enabled anacondas to reach their giant size early in their evolutionary history, cooler temperatures and shrinking ranges haven't forced the snakes to get smaller to adapt. That could suggest that these weren't the primary factors keeping the snakes large in the intervening millennia, the researchers wrote in the study.

Predator-prey interactions likely didn't play a major role in maintaining the snakes' body size, either, the researchers said. A lack of competition for food could have helped the snakes grow large in the first place. But they didn't get smaller as other predators moved into South America during the Pliocene (5.3 million to 2.6 million years ago) and the Pleistocene (2.6 million to 11,700 years ago), suggesting that food availability isn't a big factor in anacondas' giant size.

Snake quiz: How much do you know about the slithering reptiles?

Scientists finally know how venomous snakes sink their teeth into prey thanks to a series of high-speed videos.

In a new study, published Thursday (Oct. 23) in the Journal of Experimental Biology, scientists recorded various species of snakes striking fake prey, capturing footage from multiple angles and in high definition. The videos revealed three different ways that the snakes take down their dinners.

Scientists have captured the moment when a venomous snake lunges for its meal in photographs and video since the early 1950s. But the strikes happen so quickly — in as little as 0.1 seconds — that older cameras weren't fast enough to catch all the details. More recent field recordings of snake strikes, meanwhile, have often been limited by low resolution and dim lighting, researchers wrote in the new study.

To better understand how different types of snakes attack their food, researchers traveled to Venomworld in Paris, an animal facility where study co-author Remi Ksas and colleagues regularly extract venom from snakes and scorpions for medical and pharmaceutical work. There, they crafted fake prey from a muscle-like medical gel and dangled it in front of 36 species of venomous snakes while filming with multiple high-speed cameras.

While tempting the snakes to strike, "I flinched a couple of times," study co-author Silke Cleuren, a biologist at Monash University in Australia, said in a statement.

After recording more than 100 high-speed videos of 36 different snake species striking at the fake prey, the scientists spotted patterns in how these reptiles attack. The footage revealed that most vipers bit their target within 0.1 seconds of lunging — faster than most mammals' startle response, meaning their prey would be unlikely to escape. While some elapids — the family that includes the rough-scaled death adder (Acanthophis rugosus) and the Cape coral snake (Aspidelaps lubricus) — were just as fast as viperids, others took more than 0.3 seconds to reach their prey.

Different families of snakes injected their venom in different ways, too. Viperids struck quickly from a coiled position but sometimes didn't get a good angle on their bites. If that happened, the viper would pull a fang out of its prey and reinsert it in a more favorable position before injecting its venom.

Elapids took a sneakier approach, slithering up close to their prey to reduce the distance they had to lunge. They then slightly loosened their jaws and bit down again several times, "likely to prolong the venom flow into their prey," the researchers wrote in the study.

The team also observed two snakes from the colubrid family, the mangrove snake (Boiga dendrophila) and Fischer's tree snake (Toxicodryas pulverulenta). These "rear-fanged" snakes inject venom through teeth at the back of their upper jaw. When T. pulverulenta bit the fake prey, it dragged its fangs back and forth across the gel, creating crescent-shaped wounds that may help it deliver as much venom as possible.

Future studies could determine if the size of the prey has any effect on the snakes' attack, the researchers wrote in the study.

When Jacob Glanville first spoke to Tim Friede, he said, "I'd love to get my hands on some of your blood."

As CEO of the biotech company Centivax, Glanville was developing a universal snakebite treatment. And Friede is a self-taught herpetologist with hyperimmunity to some of the world's deadliest snake toxins.

Over the past two decades, Friede has had over 800 snakebites and "self-immunizations" with the venom of cobras, taipans, black mambas, rattlers and more. By carefully increasing the doses of diluted venom, he "trained" his immune system to produce antibodies that worked against a broad variety of snake venom toxins.

What Glanville needed for his "universal" antivenom were several antibodies, each of which could neutralize many different versions of a toxin. That's no small task. A snake venom is a mixture of up to 70 toxins. And different snakes can produce different combinations, variants and amounts of these toxins, even in the same species across and within geographic regions. Even small chemical variations from one toxin to the next could result in a very different reaction to a bite, making an antivenom effective against one snakebite but ineffective against another.

But Glanville suspected it was still possible to achieve his goal, because structurally, all venom toxins are variations of around 10 protein classes. That suggests that the key sites where these proteins bind to human cells could be similar across many venoms.

If researchers could find antibodies that latch onto these common binding sites,"we could make a cocktail that could be a universal antivenom," Glanville said.

He was hoping that the antibodies in Friede's blood might work against some of those similar sites. With a 40-milliliter blood sample from Friede, Glanville worked with biochemist Peter Kwong and others from the National Institutes of Health and Columbia University to create a "broad-spectrum" antivenom. In 2025, Glanville, Kwong and colleagues reported that, in mice, a mix of three agents including some derived from antibodies in Friede's blood provided broad protection against the venom of 19 snakes of the elapid family, which has about 300 species, including various cobras, mambas, taipans and kraits.

Glanville thinks his research shows that a universal antivenom is within reach. But other experts are skeptical of the need and practicality of this approach. What's needed, they say, is not a "universal antivenom." They'd rather see a suite of several antivenoms, with each one tailored to the snakes in a given geographic region and able to be made cheaply and quickly.

A toxic threat

Up to 138,000 people die of bites from venomous snakes every year, mostly in Africa, Asia and Latin America, according to the World Health Organization. These numbers may be an underestimate, however, because people who are bitten may not always seek medical treatment.

Plus, getting the right antivenom quickly is a challenge. People may not always know which snake has bitten them, as there are about 600 species of venomous snakes and often multiple venomous snake species in a given region..

Generally, the toxins in snake venom fall into three categories: neurotoxins, which damage the nervous system; hemotoxins, which disrupt blood flow and clotting; and cytotoxins, which damage cells and tissue.

Most elapids rely on neurotoxins. Among the deadliest types are three-finger toxins (3FTXs), so called because of the characteristic finger-like loops in these protein structures. The 3FTX family includes long- and short-chain neurotoxins (LNX and SNX), which are the most dangerous because they often bind swiftly and irreversibly to the receptors on muscle nerve cells, preventing them from firing.

If not counteracted, 3FTXs cause rapid muscle paralysis and death.

Developing a universal antivenom

To develop their new antivenom mixture, Glanville's team isolated DNA from Friede's blood and created a library of the antibodies in it that counteracted snake venom toxins. From these, they isolated those that neutralized many of the most dangerous ones.

"The way antivenoms work is, if you disable one [toxin], it neutralizes the whole thing," said Kartik Sunagar, an evolutionary geneticist who leads the Indian Institute of Science's Evolutionary Venomics Lab and is working to develop antivenoms for snakes found in specific regions in India. "This is how you can achieve broad neutralization, as many of these toxins are shared across species."

Glanville and colleagues found that an antibody called LNX-D09 was effective against LNXs, while another, SNX-B03, worked against SNXs. They combined these with a drug called varespladib, which was previously shown to neutralize another type of snake venom toxin, called phospholipase A2 (PLA2), which breaks down cell membranes, causing tissue death, inflammation, hemorrhage, or swelling . This cocktail protected mice from 19 venomous snake species — full protection against 13 species, and for the remaining six, it reduced the severity of symptoms. Their paper was published earlier this year in the journal Cell.

A daunting task

But the complexity of snake venoms makes developing a one-size-fits-all solution extremely daunting.

"A snakebite is not just one disease…[and] behind each snakebite is a different venom composition, The toxins important in African snakes may not even exist in any snake venom in the Americas," said Andreas Hougaard Laustsen-Kiel, a biotechnologist at the Technical University of Denmark who is working to develop broad-spectrum snakebite treatments. "The toxins important in African snakes may not even exist in any snake venom in the Americas."

Laustsen-Kiel doesn't think a universal antidote to snake venom is possible — or even necessary. "You don't make a drug where you take insulin, Alzheimer medicine, cancer medicine, a medicine against bad breath, make it into one pill, and say, hey, [if you] suffer from one of these things, here, just take our multi-drug," Laustsen-Kiel told Live Science.

He also cautioned against hyping the idea that a "universal" antivenom is near. Glanville's team's new antivenom cocktail is effective against snakes from many regions, but it works only for the venoms in the study.

"To a non-expert it might look like very broad neutralization, but all the species picked have venoms that are very similar," Laustsen-Kiel said. But the snakes highlighted in the study often have close cousins in the same regions that make venom that differs from those targeted in the new mixture, so it isn't likely to work on their venoms, he added.

Still, he said, Glanville and team's work is significant because it validates an approach that has been around for a decade. "If you go one by one, make good, broadly neutralizing antibodies, and make cocktails [of those], that is likely a good strategy for making better antivenoms."

Instead of trying to make a universal antivenom, a better approach would be to mix-and match a panel of broadly neutralizing antibodies specific to each geography, he said. This would mean targeting the venoms of snake species found in a given area, not the world over.

The century-old technology behind snake antivenom production

But there's another barrier to an ideal antivenom: Production still relies on the 125-year-old technology of injecting animals like horses or sheep with venom and using their antibodies to create antidotes for humans. There are many drawbacks to this approach. First, most snake species don't have specific antivenoms, and even if they do, their effectiveness can vary because of venom differences. Plus, nonhuman antibodies risk causing allergic reactions like anaphylaxis and serum sickness in some users.

What the field needs, Laustsen-Kiel wrote in 2024, is a way to quickly and efficiently produce human monoclonal antibodies (mAbs) — lab-made antibodies designed specifically for the human immune system — that work against many variations of the same class of toxin.

We may be closer to that goal than to a universal antivenom. In February 2024, Sunagar and colleagues reported a broadly neutralizing human mAb against a diverse array of LNXs from elapids. After testing over 50 billion synthetic human antibodies, they zeroed in on one that did the job. Their study presented a framework for developing more such antivenom treatments.

The secret to such broad neutralization, Sunagar told Live Science, is that if you disable one key component in snake venom, it neutralizes the venom entirely. So you would only need to find one specific antibody that could be effective against many venoms with similar toxins.

Their synthetic antibody neutralized whole venoms of the king cobra (Ophiophagus hannah) in the Western Ghats in India, the monocled cobra (Naja kaouthia) in eastern India, the many-banded krait (Bungarus multicinctus) in Southeast Asia, and the black mamba (Dendroaspis polylepis) in sub-Saharan Africa.

"Achieving broad neutralization is not a challenge anymore," Sunagar told Live Science. "The only challenge would be to mass-produce these antibodies and make them available to snake projects."

That's because the more components an antivenom treatment has, the more expensive it becomes, making it economically infeasible to produce and distribute in developing countries, which bear the brunt of snakebites, he added.

While Glanville believes a universal antivenom is possible, his antivenom cocktail has yet to be tested in humans. His company is in talks with a veterinary group in Australia to try out the cocktail in pet dogs with snakebites. They are also looking at creating a similar mixture of broadly neutralizing antibodies for the viper family.

On the other side of the world, Sunagar's lab is working on an antibody against vipers in India. His idea of a universal antivenom is not a single product.

"Theoretically, it's possible to make such an antivenom, but I don't think that's necessarily the best solution," he said. Rather, he sees a combination of two or three products for different regions that would neutralize a much broader spectrum of snake venoms than is currently available.

Meanwhile, Glanville's team is now developing an antivenom to counteract bites from the other major venomous snake family, the vipers.

“We're running the same game plan that we did on the elapids...[and] building a second cocktail,” Glanville said.

A Burmese python in Florida's Big Cypress National Preserve vomited up an entire white-tailed deer after temperatures in South Florida dipped below 50 degrees Fahrenheit (10 degrees Celsius) late last year, well below the cold-blooded creature's comfortable range.

While pythons are known to vomit their meals in cold laboratory settings, scientists had never caught the elusive snakes doing it in the wild — until now. The unusual observation, made in late November 2024, is described in a study published in July in the journal Ecology and Evolution.

"Almost every day is a surprise," Mark Sandfoss, senior author of the study and a biologist at the U.S. Geological Survey (USGS), told Live Science. "Pythons are constantly doing things I never imagined, but this is such a beautiful moment where science and basic principles line up with field observations."

Burmese pythons (Python bivittatus) have been an invasive species in Florida since the late 1970s. Despite this decades-long presence, they are largely understudied, and there are gaps in knowledge about the snakes' biology and how they interact with native species, such as deer.

Deer numbers are declining in the preserve, which is concerning because they form an important part of the diet of local predators, like Florida panthers (Puma concolor coryi). To learn more about how often snakes eat deer and how quickly they digest them, scientists at the preserve spent a year tracking the digestion of several large female pythons — those deemed most likely to eat a deer.

One snake under observation had a large lump in its stomach, indicating that it had eaten something deer-sized. Over the next several days, though, this lump did not appear to get any smaller.

After a cold night, when temperatures dipped to 48.9 F (9.4 C) in the preserve, scientists revisited the snake. They found it lump-free, swimming in the shallow water of a willow swamp near a minimally digested white-tailed deer (Odocoileus virginianus) that it had vomited up.

Related: Scientists discover Burmese pythons have never-before-seen cells that help them digest entire skeletons

"They found her very empty, and they were able to smell a deer not far away and put two and two together," Sandfoss said.

Because snakes are cold-blooded, or ectothermic, they find it difficult to function in the cold. Their biological processes, including digestion, slow down until the temperature warms back up.

If the outdoor temperature gets too cold, a snake's meal can start decomposing in its stomach faster than the snake can digest it, causing bacteria to build up. The snake's response is to vomit to eliminate the bacteria. This can be an energy-intensive activity for an already hungry snake, but the snake in the study survived it.

Because the Burmese python is an invasive species in Florida, the snake's survival has complex implications, Sandfoss said. It missed one of the large meals it takes only a few times a year, so it might lack the energy to reproduce, which could help control the python population. Alternatively, the snake may kill another deer to make up the lost energy, further endangering the deer population native predators rely on.

"Deer in Big Cypress have been declining for several years, and we believe pythons to be a factor in that," lead author Travis Mangione, a biologist at the National Park Service (NPS), told Live Science. "Because this python survived the vomiting event, it will keep eating native wildlife."

Even as scientists work to understand how Burmese pythons' vomiting events affect the local ecosystem, observations of it in the wild hold valuable clues to how far this invasive species can spread within the United States. Temperature is a key limiting factor for the snakes' range, and the coldest temperature they can survive might be the coldest in which they can digest, Sandfoss said.

The new study fits within a larger, not-yet-released research project that's analyzing the full year of python feeding data. The scientists working on the project hope it will shed light on the basic biological process of digestion in Burmese pythons, which is still under-researched.

"Pythons have complicated biology, and we've never really dealt with an animal like this at this scale — this large, invasive ectotherm, terrestrial," Sandfoss said. "We're trying to figure all these things out."

Snake quiz: How much do you know about the slithering reptiles?

Turtles and tortoises are both reptiles with shells, but they're not exactly the same. So how can you tell them apart? What's the difference between a turtle and a tortoise?

"All tortoises are turtles, but not all turtles are tortoises," Sydnee Fenn, a reptile keeper at Columbus Zoo and Aquarium, told Live Science. Generally, the reptiles that people call turtles spend a great deal of time in the water, whereas tortoises live on land, according to Genius Vets in San Diego, California.

Many of the differences between turtles and tortoises come from this habitat difference. For example, water-dwelling turtles' shells are usually flattened to help them swim in lakes, rivers or oceans. Tortoises do not swim, so their shells are often shaped like domes instead, Genius Vets notes, which has advantages on land.

"When tortoises are walking, they can flip onto their backs by accident, and the domed shape of their shells can help them flip back onto their feet," Fenn said. "Also, the dome shape allows more space inside, so some can retract all of their limbs into the shell."

Related: Why do turtles live so long?

There are exceptions to this rule, however. For instance, "the pancake tortoise from Africa does not have the domed, solid carapace of other tortoises," Brett Baldwin, curator of herpetology and ichthyology at the San Diego Zoo, told Live Science. "It has evolved a shell that is flat, less heavily calcified, and pliable, which allows it to scurry quickly into rock crevices and wedge itself in by inflating its pliable carapace."

Turtles that spend time in both the water and on land have webbed feet that can help them swim as well as maneuver on the ground if needed. Fully aquatic turtles, such as sea turtles, have flippers, according to Genius Vets. In contrast, tortoises usually have round feet and stumpy legs, the San Diego Zoo notes.

"Having shorter, stouter, more stable legs allows for easier mobility to carry the heavy shell in their terrestrial lifestyles," Baldwin said. For instance, Fenn noted that for desert tortoises, "wide feet help them walk across sand easier, just like camel feet."

Generally speaking, non-tortoise turtles are omnivorous, and tortoises are herbivorous, Fenn said. Because non-tortoise turtles can swim, they can move fast enough to catch prey in the water, thus broadening their diet, she said. In contrast, tortoises are famously slow on land, so they usually stick to plants.

That said, "tortoises can opportunistically eat meat," Fenn said. "They're not going to actively hunt like a tiger would, but if there's meat," such as insects or carrion, "they might eat it." In addition, some turtles, such as the green sea turtle (Chelonia mydas), are herbivorous, according to the National Oceanic and Atmospheric Administration.

Tortoises are found on every continent except Australia and Antarctica, generally in warm to hot environments, such as deserts and jungles, according to the International Fund for Animal Welfare. Turtles live on every continent except Antarctica, and sea turtles spend their lives in oceans spanning the globe, Genius Vets notes. Turtles' aquatic nature helps them survive even when air and ground temperatures get cold, Fenn said.

"They can go to deeper waters where temperature might stay warmer, especially in the winter," she explained. "Some turtles are able to actually breathe underwater through their cloacas, which makes it easier to hide under frozen water. All in all, the fact that they can live in cooler climates opens up where they can be found in the world."

A "most remarkable" monster's fossilized remains from Jurassic Germany is a never-before-seen species, a new study reports.

The marine reptile, which swam in prehistoric oceans about 183 million years ago, has been given the name Plesionectes longicollum, which translates to "long-necked near-swimmer."

P. longicollum is a type of plesiosauroid, an extinct group of long-necked, carnivorous marine reptiles that swam in Earth's oceans during the time when dinosaurs dominated terrestrial environments. This specimen lived during the early Toarcian age (183 million to 174 million years ago) during the Early Jurassic.

The fossilized specimen is about 10 feet (3 meters) long, similar to the length of an alligator, with its neck accounting for slightly less than half of its total span.

The nearly-complete skeleton of the animal contained remnants of fossilized soft tissue and bone, which enabled scientists to determine that P. longicollum is indeed a newly-discovered species — a conclusion past studies were hesitant to make.

The reptile's bones were originally excavated in 1978 from a quarry in Germany, part of the Posidonia Shale formation, which is known for its "exquisitely preserved fossils," according to the study. "This specimen has been in collections for decades, but previous studies never fully explored its distinctive anatomy," study lead author Sven Sachs, a vertebrate paleontologist at the Natural History Museum of Bielefeld in Germany, said in a statement from the museum.

Related: Oldest tadpole on record was a Jurassic giant

The findings were published in the journal PeerJ on Aug. 4.

"Our detailed examination revealed an unusual combination of skeletal features that clearly distinguish it from all previously known plesiosaurs," Sachs said. The work demonstrated that the Posidonia Shale beds contained a higher degree of reptile diversity than previously thought.

The new specimen is the oldest known plesiosaur from the town Holzmaden in southwest Germany, according to the statement. The animal was not yet an adult when it died, but based on its anatomy, researchers were able to classify it into a new genus and species.

Five other almost complete Plesionectes skeletons have been identified at the Posidonia Shale and include examples of all three major plesiosaur lineages.

"This discovery adds another piece to the puzzle of marine ecosystem evolution during a critical time in Earth's history," study co-author Daniel Madzia, a paleobiologist at the Polish Academy of Sciences, said in the statement. The period when P. longicollum lived "was marked by significant environmental changes, including a major oceanic anoxic event that affected marine life worldwide," he said. The event, which depleted oxygen and spiked acidification in the water, led to a severe loss of marine biodiversity, including an extinction event killing around 5% of global families on land and in the sea.

This fossil is permanently housed at the Stuttgart State Museum of Natural History in Germany.

Researchers found that specialized cells in Burmese pythons' (Python bivittatus) intestinal lining process calcium from the bones of their meals. This helps explain how these predators digest whole prey.

The team published its findings June 25 in the Journal of Experimental Biology.

Burmese pythons typically dine on birds and small mammals, though they don't need to eat every day. The snakes swallow their prey whole and spend several days digesting their meal before hunting again.

As part of digestion, pythons break down their prey's bones. The bones provide necessary calcium in the snakes' diet — but the pythons can't use all the calcium. "We wanted to identify how they were able to process and limit this huge absorption of calcium through the intestinal wall," study co-author Jehan-Hervé Lignot, a biologist at the University of Montpellier in France, said in a statement.

To examine how the snakes managed their calcium intake, the researchers fed Burmese pythons one of three diets: a regular diet of whole prey; a low-calcium diet with boneless prey; and a diet with boneless prey and a calcium supplement. After several meals, the team studied the effects of each regimen on the snakes' intestines.

The team found that narrow, specialized cells in the pythons' intestinal lining played a role in digesting bones. In the snakes that ate whole prey or boneless prey with a calcium supplement, these cells held particles made up of calcium, iron and phosphorus. But these particles weren't present in snakes that only ate boneless prey.

Related: 'An up-tempo version of Darwinian evolution': How a mega freeze in Florida may have caused Burmese pythons to evolve at a blindingly fast speed

The cells may be involved in dispelling calcium that the snakes couldn't absorb. It's possible that the cells could concentrate the extra calcium into the particles, then release the particles alongside other undigested components into the snakes' feces, the researchers wrote in the study.

Since discovering the narrow intestinal cells in Burmese pythons, the scientists have also found them in the intestines of other pythons and boas, as well as in Gila monsters (Heloderma suspectum) — all of which eat their prey whole. But there's no evidence yet that other animals that swallow their entire prey, such as dolphins or fish-eating birds, produce these calcium particles.

Further studies could reveal just how widespread these bone-digesting cells are in the animal kingdom, the researchers wrote.

"Marine predators that eat bony fish or aquatic mammals must face the same problem" of digesting bones and ridding themselves of excess calcium, Lignot said in the statement. "Birds that eat mostly bones, such as the bearded vulture [Gypaetus barbatus], would be fascinating candidates too."

Mysterious night lizards survived the giant asteroid strike that ended the reign of the dinosaurs 66 million years ago, despite living right next to the impact site, a new study finds.

Thanks to a new evolutionary analysis, researchers discovered that the little lizards, in the family Xantusiidae, were living around the Gulf of Mexico before and after the asteroid struck what is now Mexico's Yucatán Peninsula. This makes night lizards the only group of land vertebrates known to have survived close to the impact location, and still have members living in the region today.

The dinosaurs' doomsday asteroid was around 7.5 miles (12 kilometers) wide and caused widespread devastation when it hit at the end of the Cretaceous period (145 million to 66 million years ago). The impact was catastrophic for much of Earth's wildlife, triggering the Cretaceous-Paleogene (K-Pg) mass extinction event, in which around 75% of all species died out. However, two lineages of night lizard managed to persist through the disaster, despite likely being close enough to see the impact.

"They would have been all around the margin of the asteroid impact," study lead author Chase Brownstein, a doctoral candidate in the Department of Ecology and Evolutionary Biology at Yale University, told Live Science.

How did night lizards survive amid all the devastation? Researchers aren't sure, but Brownstein noted that they have slow metabolisms, so they wouldn't have needed to eat very often.

The researchers published their findings Wednesday (June 25) in the journal Biology Letters.

Related: Iguanas sailed one-fifth of the way around the world on rafts 34 million years ago

Night lizards grow to only a few inches in length. Often very secretive, the lizards live in specialized microhabitats, like inside rock crevices and dense vegetation, or beneath bark and logs.

Some previous studies suggested that night lizards' "crown" group — the group containing the last common ancestor of all living night lizards — evolved during the age of dinosaurs, which would have meant the animals persisted through the K-Pg devastation. The new study put that hypothesis to the test.

Brownstein and his colleagues reconstructed the ancestry of the three living night lizard genera (Lepidophyma, Xantusia and Cricosaura). They used molecular clock dating to estimate when the night lizards evolved, based on their mutations and the rate at which mutations occur in DNA over time.

The researchers found that the most recent common ancestor of living night lizards emerged during the Cretaceous around 90 million years ago and that night lizards have been living in North America and Central America since around that time, well before the asteroid struck 66 million years ago, according to the study.

The new findings suggest that two night lizard lineages survived the asteroid strike. One of these lineages then gave rise to Xantusia, which ranges from the southwestern U.S. into Mexico, and Lepidophyma, which ranges across parts of North America and Central America. The second lineage then gave rise to Cricosaura and its only species, Cuban night lizards (Cricosaura typica), in Cuba.

Night lizards weren't the only animals to survive the K-Pg mass extinction event. We wouldn't be here today if some of the mammal family tree hadn't lived through the asteroid impact. Avian dinosaurs (birds), fish and plenty of other animals survived, too. However, night lizards are the only known surviving group of terrestrial vertebrates that have remained endemic to — living only in — North America and Central America since the asteroid hit.

Brownstein noted that some lineages of turtles and other lizards in the region probably survived the asteroid in a similar way as night lizards (scientifically named xantusiids) did. However, these other lineages have since disappeared.

"The problem is that they just aren't there anymore," Brownstein said. "So, what's interesting is that xantusiids have persisted and have remained endemic to the region."

A Florida bobcat has managed to take down a Burmese python in what wildlife biologists are calling a win for native Everglades predators.

Scientists are still investigating how and when local predators face off against the invasive snakes, but the finding hints that native species are learning to take advantage of the competition as a potential food source.

The snake's remains were found near the city of Naples in December 2022 by wildlife biologist Ian Bartoszek of the Conservancy of Southwest Florida.

Since 2013, he and his colleagues have used radio trackers to keep tabs on male Burmese pythons, and during breeding season, these male "scout" snakes lead researchers to fertile female snakes and their eggs. From there, researchers remove and euthanize the reptiles in an attempt to cull the invasive population.

On that chilly December day, Bartoszek's team was tracking Loki, a 13 foot (4 meters) long, 52 pound (23.5 kilogram) scout snake. They expected to find Loki holed up with a female python. Instead, they found his freshly slain body, with the head and neck gnawed off and buried beneath pine needles nearby.

"It was a bit sad and a bit exciting at the same time," said Bartoszek, who had tracked Loki through six breeding seasons. "We sort of treated it as a bit of a CSI crime scene."

The team immediately started to look for clues as to what had killed the massive snake. The way Loki's neck had been chewed and his head buried suggested a large cat — either a bobcat or a Florida panther — as the culprit.

Bartoszek contacted wild cat expert David Shindle, of the US Fish and Wildlife Service, who set up a trail cam near the kill site in case the cat came back for its buried meal. The next morning, it did — and its behavior was caught on video.

"All of a sudden, out of the background, an adult bobcat comes walking in across a log," Bartoszek described. "You could see it sort of sniffing the air, probably picking up on our scent, seeing what information it was clueing-in to, and basically returning to the kill site."

Burmese pythons have been known to eat bobcats, but Bartoszek suspects this particular bobcat seized an opportunity to pick off Loki while he was incapacitated. A cold snap had hit southern Florida a few days before the scientists found the snake's remains. And since male snakes are usually out and about looking for females during breeding season, the chilly weather may have left the cold-blooded Loki stunned and sluggish, far from his usual warm burrow and unable to fight off the predator.

Working on the front lines of these wildlife studies offers the chance to observe new and interesting predator-prey interactions, Bartoszek told Live Science. "It felt like 'score one for the home team,' where our native animals are fighting back," he said. "That's a good sign."

These kinds of predation events are likely becoming more common in the Everglades, Bartoszek said. His team found the remains of a different scout snake after another cold snap earlier this season, this one likely killed by a black bear.

Researchers are still collecting evidence and looking for trends in how predators like bobcats and bears might be turning the tables on pythons.

"There's a bit of a pattern emerging that — and you'd expect as much — over time, the ecosystem is rebalancing itself. It's fighting back," Bartoszek said. "These native predators are recognizing Burmese pythons as a new food source and are able to take advantage of some of their vulnerabilities."

Snake quiz: How much do you know about the slithering reptiles?

Reptiles as we know them today may have evolved about 30 million years earlier than we initially assumed, new footprints reveal.

According to a study published Wednesday (May 14) in the journal Nature, fossilized tracks found in Australia may have been left by the clawed feet of a small reptile-like creature about 350 million years ago, during the Carboniferous period.

This new discovery would push back the evolution of these animals by roughly 30 million years, as early reptiles were previously thought to have evolved around 320 million years ago.

"Once we identified this, we realised this is the oldest evidence in the world of reptile-like animals walking around on land — and it pushes their evolution back by 35-to-40 million years older than the previous records in the Northern Hemisphere," study co-author John Long, a strategic professor of palaeontology at Flinders University in Australia, said in a statement.

"The implications of this discovery for the early evolution of tetrapods are profound."

Modern reptiles, along with birds and mammals, are part of a group of animals known as amniotes, which are defined as tetrapod vertebrates (four-limbed animals with backbones) that lay eggs equipped with a protective membrane that surrounds the embryo. This so-called amnion allows eggs to be laid on land, freeing early land animals from dependency on water for reproduction. This is in contrast to amphibians, which rely on moist environments to reproduce.

Related: Which animal species has existed the longest?

Amniotes evolved from amphibian-like ancestors, with the earliest amniote body fossils being dated to the late Carboniferous Period, which spanned from approximately 359 to 299 million years ago. These early amniotes, which were small, lizard-like creatures, then diversified into two groups: synapsids and sauropsids, which evolved into the earliest ancestors of mammals and reptiles, respectively.

Based on the fossil record, amniotes were thought to have evolved around 320 million years ago. However, this new discovery of clawed amniote footprints in Australia from 350 million years ago throws these estimations hugely off.

"I'm stunned," study co-author Per Ahlberg, a professor of paleontology at Uppsala University, said in a statement. "A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved."

These footprints were discovered on a 20-inch (50cm) rock slab by two amateur palaeontologists in the Snowy Plains Formation in Australia's Victoria, which dates back to 350 million years ago. The footprints appeared to have been made by a creature with clawed feet and long toes, likely an early sauropsid, meaning that reptiles may have been around much earlier than we assumed.

"Claws are present in all early amniotes, but almost never in other groups of tetrapods," Ahlberg said. "The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile."

These footprints are the earliest clawed prints ever discovered.

"When I saw this specimen for the first time, I was very surprised," study co-author Grzegorz Niedźwiedzki, a researcher at Uppsala University, said in the statement.

Pushing back the tree of reptilian evolution, the researchers concluded that reptiles may have actually evolved towards the end of the Devonian period, when primitive fish-like creatures like Tiktaalik roamed the land.

"It's all about the relative length of different branches in the tree," Ahlberg said. "In a family tree based on DNA data from living animals, branches will have different lengths reflecting the number of genetic changes along each branch segment. This does not depend on fossils, so it's really helpful for studying phases of evolution with a poor fossil record."

Niedźwiedzki added: "The most interesting discoveries are yet to come and that there is still much to be found in the field. These footprints from Australia are just one example of this."

Researchers have identified two new crocodile species living on isolated islands in the Caribbean — and they're both threatened with extinction, a new study has found.

The reptiles, previously thought to be American crocodiles (Crocodylus acutus), separately inhabit the island of Cozumel and the atoll of Banco Chinchorro off Mexico's Yucatán Peninsula. Both populations have around 500 individuals.

Scientists identified the as-of-yet unnamed species while studying the genetics of crocodiles across Mexico's Pacific coast, Central America and the Caribbean. The team found stark genetic differences between the Cozumel and Banco Chinchorro populations and the rest of the American crocodile species, concluding that the island crocodiles were separate species, according to a statement released by McGill University in Canada.

"These results were totally unexpected," study lead author José Avila-Cervantes, who carried out the genetics research during his graduate studies at McGill University, said in the statement. "We assumed Crocodylus acutus was a single species ranging from Baja California to Venezuela and across the Caribbean."

The researchers' findings will appear in the upcoming June volume of the journal Molecular Phylogenetics and Evolution — they were first published online on March 28.

Related: Crocodiles are overheating due to climate change — and it's changing their behavior

American crocodiles live across 18 countries, ranging from the southern tip of Florida to the Caribbean and northern South America. They share some of that range with Cuban crocodiles (C. rhombifer) in Cuba and Morelet's crocodiles (C. moreletii) in Mexico, Guatemala and Belize.

The researchers were studying variation across all three species when they identified the two new species on Cozumel and Banco Chinchorro. Their work involved capturing and releasing crocodiles to extract blood and tissue samples for DNA analysis. The team also used genetic data from previous studies and compared physical differences between the crocodiles, according to the study.

The main physical difference between the different species is that their skulls vary in length and shape. For example, the Banco Chinchorro crocodiles have a longer and broader snout compared to those of Cozumel Island, according to the study.

The discovery of two new species could be important from a conservation perspective. Crocodiles in the region are already under threat from human activities including urbanization, pollution and tourism. The researchers found the populations on Cozumel and Banco Chinchorro appear to be stable, but that they are vulnerable due to their small size and restricted habitat, according to the statement.

"Now that we recognize these crocodiles as distinct species, it’s crucial to protect their habitats," Hans Larsson, a biology professor at McGill University and the study's principal investigator, said in the statement. "Limiting land development and implementing careful conservation strategies on Cozumel and Banco Chinchorro will be key to ensuring their survival."

Crocodile quiz: Test your knowledge on the prehistoric predators

Four endangered baby tortoises have made their highly anticipated public debut at the Philadelphia Zoo as the first hatchlings of their 100-year-old mother, Mommy.

Mommy, a western Santa Cruz Galápagos tortoise (Chelonoidis niger porteri), made international headlines earlier this month for becoming the oldest first-time mom of her species. Mommy's exact age is unknown, but she is around 100 years old and has been at the zoo for more than 90 of those.

The new babies mark the first time Philadelphia Zoo has bred western Santa Cruz Galápagos tortoises in its more than 150-year history. Western Santa Cruz Galápagos tortoises are critically endangered in their native home of the Galápagos Islands, and there are fewer than 50 kept in U.S. zoos.

The zoo unveiled Mommy's four baby girls on Wednesday (April 23), as eager press representatives lined up to get photographs and video of the new star attractions. Wednesday also marked the 93rd anniversary of Mommy's arrival at the zoo.

"THEY'RE FINALLY HERE!" a spokesperson for Philadelphia Zoo wrote in a Facebook post. "Mommy the Galapagos tortoise’s four baby girls have just made their public debut inside the Reptile and Amphibian House in honor of today marking 93 years of Mommy at the Zoo."

Related: World's oldest tortoise still randy at 191 years old

Western Santa Cruz Galápagos tortoises are a subspecies of the Galápagos tortoise, which is the largest tortoise species on Earth. Males — typically larger than females — can grow up to around 1.8 meters (6 feet) in length, and weigh up to around 570 pounds (260 kilograms), according to the San Diego Zoo Wildlife Alliance.

Human activity has driven several Galápagos tortoise species to extinction, while western Santa Cruz Galápagos tortoises number just a few thousand. The tortoises have historically suffered from people hunting them for meat, and have had their ecosystem disrupted by invasive species including predators like cats and rats, which prey on young tortoises and their eggs, according to the International Union for Conservation of Nature Red List.

Mommy's new babies are part of a captive breeding program in U.S. zoos to help safeguard western Santa Cruz Galápagos tortoises. Because Mommy had never bred before, this is the first time she has passed on her genes, helping to keep the captive population genetically diverse and healthy.

"These newest additions represent a new genetic lineage and some much-needed help to the population of this critically endangered species in human care," the zoo's spokesperson said.

The babies could have a long life ahead of them. Researchers don't know the maximum lifespan of Galápagos tortoises, but one individual was recorded reaching the age of 171, according to the San Diego Zoo Wildlife Alliance. Once tortoises reach maturity, they usually remain reproductively active for the rest of their life, and can keep breeding long into old age.

Fifteen years ago, a cold snap froze much of Florida's wildlife to death — including many of the state's invasive Burmese pythons (Python bivittatus). But in this excerpt from "Slither: How Nature's Most Maligned Creatures Illuminate Our World" (Gand Central Publishing, 2025), science writer Stephen Hall reveals that a subset of these pythons were genetically predisposed to survive the cold, setting the stage for rapid evolution that could help the invasive snakes spread further into North America.

In early January 2010, a historic and prolonged deep freeze swept across the southeast United States, reaching all the way into the subtropical Everglades. Temperatures hovered around 50 degrees Fahrenheit (10 degrees Celsius) for 48 hours; on Jan. 11, thermometers in South Florida dipped as low as 24.8 F (minus 4 C). Most people remember it, if at all, for the frozen iguanas that dropped out of trees and photos of citrus trees encased in icicles, like some fugitive Minnesota winter carnival smuggled into the Deep South.

But to wildlife and invasive species experts, the Big Freeze marked the start of the Big Unplanned Experiment.

The immediate impact on the Burmese python population was clear. Carcasses of dead snakes littered roads; frozen specimens turned up in underground burrows; farther north in South Carolina, in the infamous "Where's Waldo" python enclosure, all 10 snakes perished during the regional cold snap.

Researchers attributed the mass die-off to "maladaptive behavior," meaning many snakes tried to bask above ground in the sun despite the frigid temperatures, rather than seeking thermal shelter in underground or aquatic burrows. Python "removals" — captures by hunters, which served as a rough indication of the general population — had peaked in 2009 in the national park but plummeted almost five-fold in the following two or three years. It all looked like good news, at first.

But population numbers were still lacking, and "models" are still just models. Genes are where the rubber of biology meets the road of environmental challenge, and this is when the geneticists entered the story. They were less interested in the many snakes that had died, and more interested in the few that had survived.

Like all snakes, Burmese pythons are ectotherms — they rely on warmth from the environment because they do not generate their own metabolic heat — so they have to develop biological tricks in their behavior or in their physiological resilience in the face of life-threatening cold to survive freeze events that do not occur in their native range. As the United States Geological Survey (USGS) overview put it, "some portion of the southern Florida population survived" the 2010 event, "and these snakes and their offspring make up the current population."

By 2014, the number of python removals in Everglades National Park had returned to pre-freeze levels. In genetic parlance, the 2010 freeze was a "bottleneck event" — only a few squeezed through and survived. But the ones that did, in the biblical sense, went forth and multiplied.

Beginning around the year 2015, several researchers studying python genomes to understand their metabolism became curious about the after effects of the big freeze. Daren Card and Todd Castoe of the University of Texas at Arlington teamed up with Maggie Hunter of the USGS office in Fort Lauderdale to look for evidence of what is called rapid adaptation, which might be thought of as an up-tempo version of Darwinian evolution.

They examined the DNA of these survivor snakes to see if there were any genetic clues as to why certain pythons were able to withstand an extended freeze; more precisely, they compared the DNA of pythons that lived before the freeze event with the DNA of pythons that had survived to see if they could identify any differences that might explain the resilience of the survivors at the molecular level.

The short and disturbing (although not definitive) answer was: yes.

It turns out that the survivors seemed to share genetic changes in areas of their genomes known to control thermoregulatory behavior and metabolism. "We saw a lot of things that just fortuitously overlapped with a lot of the same sorts of pathways and genes that we were studying in parallel, in a much more controlled fashion, using more lab experiments in Todd's work on Burmese pythons," Card told me. "As we delved into them, we started to see a lot of genes that are involved in things like thermal tolerance."

The findings, published in 2018, suggested that the survivors shared variations in their genetic makeup that seemed to confer greater cold tolerance and greater metabolic flexibility — two traits that Castoe's lab had been investigating since 2011. These snakes were more inclined behaviorally to seek shelter in underground refugia to outlast the cold — a good adaptation to the environmental reality of occasional freezes. And the metabolic changes seemed to favor a behavior that encouraged smaller and more frequent meals — a good adaptation to the ecological reality that, having already decimated populations of large mammals in the Everglades, the pythons might need to modify their diet.

This is not definitive news — the study was small, no one (surprisingly) has followed up on it, and, as Card put it, researchers still only have a view from 30,000 feet of what happened on the genetic level in the pythons that survived the Big Freeze. Whatever it is, the genetic changes — or, more accurately, the selection for genes that enhanced survival — appears to have happened very quickly. And that is, possibly, very bad news. It suggests that the pythons are on the move, genetically as well as geographically.

The implication is that the 2010 freeze acted as a huge selection event, as evolutionary biologists put it — an environmental stress so dire, so extreme, that it has the effect of rapidly winnowing out individuals holding a bad genetic hand and "selecting" the lucky ones that hold winning genetic hands.

The freeze culled out individuals that were susceptible to cold temperatures and selected individuals that possessed, at the genetic level, some form of cold-hardiness. Those genes were presumably passed down — immediately, profligately and of course, cryptically — to their hundreds of offspring.

The suggestion of rapid adaptation in the Burmese python population in Florida again contradicts our traditional notions of evolution as a glacial process of genetic selection and refinement that requires millennia, eons and geological epochs. "We typically think of evolution as occurring over generally quite long time scales, on the order of several generations at the low end up to potentially thousands to millions of years," Card said. "I think with a lot of the tools that we've developed more recently, especially in things like genomics, people have taken a harder look at how quickly evolution can occur… And generally, when you see such an extreme thing occurring, it really suggests that there's very strong selection. Something's happening."

In fact, Castoe believes the importation of so many pythons from so many different regions of Asia — all packing in their biological luggage a wide variety of genetic variants, known as alleles, for their trip to North America — set the table for a rapid genetic adaptation. As Castoe put it: "If you've got a good amount of genetic variation, given strong selection, this can happen in a heartbeat. 'If I've got the allele, what the hell am I waiting for? I ain't waiting for nothing!'"

At a time when roughly 40% of Americans do not accept the notion of evolution, the pythons that survived the Big Freeze in Florida appear to believe in it 100%. The take-home genomics message from the snakes is that evolution is real, it's apparently happening at blindingly fast speed, and it argues that the 2010 cold snap may have created a subset of pythons better able to survive cold temperatures — and thus better adapted to spread beyond the northern boundaries of its current range.

Excerpted from SLITHER: How Nature’s Most Maligned Creatures Illuminate Our World ©2025 Stephen S. Hall and reprinted by permission from Grand Central Publishing/Hachette Book Group.

Do you ever wish you could just crawl out of your own skin? Snakes are some of the few creatures on Earth that actually can. Dozens of times throughout its life, a snake slithers out of its old skin in a process called "ecdysis," leaving behind papery sheds delicately imprinted with the unique pattern of its scales.

It's not unusual to shed skin; humans do it, too. "But unlike us, whose skin sheds off in little flakes, snakes produce a whole new layer of skin, and the old layer of skin falls off in one big slough," said Jason Dallas, a postdoctoral researcher who studies bacterial-fungal interactions in snakes and amphibians at Middle Tennessee State University.

But why do snakes shed their skin, and why does it happen in one go?

Snake skin is composed of two main layers. The inner, softer layer — called the dermis — contains the pigments that give snakes their intricate colors and patterns. The dermis is covered in the epidermis, a tougher layer of semitransparent keratin scales.

The outer layer of human skin also contains keratin, but the structure of our skin allows it to flake off in individual scales, which are almost invisible to the naked eye. In snakes, the exterior keratinous layer forms a unit, which creates a sheath-like covering that's bound to the snake's more delicate dermis below.

Related: What are the world's deadliest snakes?

The trade-off of this hardy external layer is that it doesn't expand; it remains relatively inflexible and constricts the snake as it grows. This is one of the primary reasons snakes shed their skin: to create more room. Snakes grow more quickly when they are younger, so they also shed more in youth.

In fact, snakes' first shed happens "within a few days of hatching or being born," Daniel Kane, senior reptile keeper at the London Zoo, told Live Science in an email. By adulthood, snakes typically shed around three or four times a year, Kane said.

When a snake is almost ready to shed, it starts to develop a second fresh keratin layer atop the dermis and below the original keratin sheath. It also secretes a fluid to help loosen the old layer from the new one. As this process unfolds, the snake typically finds a rough spot to rub its head against. This creates a slit in the old skin, through which the snake can then start to slither out.

With the help of continued rubbing and muscle spasms, the snake eventually loosens its entire skin and escapes the wrinkled relic with a set of glossy new scales. A fresh shed may be up to 20% longer than the original snake, as this recently lubricated skin is "quite stretchy before it dries out and becomes brittle," Kane explained.

Once the skin is shed, the snake discards it and slithers away. Although snakes don't typically eat their skins, some other reptiles do, such as lizards and geckos, to regain lost nutrients.

Shedding is associated with big life events, such as a snake's emergence from a long hibernation, or reproduction. "They typically will shed right before they either lay their eggs or give live birth, and then they may shed again after that period," Dallas told Live Science. "So it typically is synced up with life history events in adults."

Interestingly, snakes also use shedding to deal with unwanted parasites, infections and disease, Dallas said. One common example is snake fungal disease, which poses a significant threat to snakes worldwide.

"The pathogen is able to colonize deeper tissues as well as internal organs," Donald Walker, an assistant professor of biology at Middle Tennessee State University and principal investigator of the lab where Dallas works, told Live Science. "It's thought to be able to get the eyes, and maybe even the brain, of the animal. … But it starts by colonizing the skin and feeding on keratin and lipids in snake scales." Shedding could be lifesaving in cases like this. Yet the ability to shed skin also incurs a cost. Not only is it an energy-intensive process, but the trailing skin may hinder the snake's hunting prowess by disturbing its vision. Snake eyes appear clear, but they're covered by a single, bubble-like, keratin scale.

"The transparent scale, known as the 'spectacle,' protects the snake's eyes from day-to-day scratches and abrasions as it moves headfirst through the world," Kane said. "When the snake is in the process of sloughing off its skin, vision is impaired by the cloudiness caused by the secretions used to separate the old from the new layers."

A less-mobile, sight-impaired shedding snake is typically more vulnerable to predators, too. So ideally, a snake should not be shedding too frequently.

Disease might complicate snakes' natural shedding schedules and turn this survival tactic against them — particularly in species such as the eastern massasauga rattlesnake (Sistrurus catenatus) in the United States, Dallas said.

"These snakes are very susceptible to the fungus that can obscure their eyes and their mouth, but also increased shedding rates can increase their risk of predation," Dallas said. "And this has caused relatively large population declines in some populations of the species."

Overwhelmingly, however, a snake's shedding ability is vital to its survival. In the wild, discarded skins can also help scientists and conservationists protect these reptiles, by offering telltale genetic fingerprints and other clues that enable them to detect threats to snake health, study population numbers and species biodiversity.

"Snake skin often contains a faint version of the pattern of the snake and the specific number and arrangement of scales, meaning it's often possible to identify a species based on a shed skin," Kane said.

Of all animals, snakes produce the most instantly recognizable shed specimens in the wild. But they share their shedding ability with all other reptiles, which, unlike their serpentine cousins, mostly release their skins in fragments. There are some exceptions, however. For example, lizards from the Abronia genus are small, dragon-like creatures that wriggle out of their skins and leave behind a perfectly intact replica, legs and all.

Snake quiz: How much do you know about the slithering reptiles?

An endangered giant tortoise has become the oldest first-time mom of her species after having her first babies at around 100 years old.

Philadelphia Zoo recently hatched eggs laid by an elderly western Santa Cruz Galápagos tortoise (Chelonoidis niger porteri), named Mommy. Her exact age is unknown, but Mommy has been at the zoo for more than 90 years.

Western Santa Cruz Galápagos tortoises are critically endangered in their native home of the Galápagos Islands, and there are fewer than 50 kept in U.S. zoos. This is the first time Philadelphia Zoo has hatched western Santa Cruz Galápagos tortoises in its more than 150-year history, according to a statement released by the zoo.

"This is a significant milestone in the history of Philadelphia Zoo, and we couldn’t be more excited to share this news with our city, region, and the world," Jo-Elle Mogerman, the president and CEO of Philadelphia Zoo, said in the statement. "Mommy arrived at the Zoo in 1932, meaning anyone that has visited the Zoo for the last 92 years has likely seen her."

Related: World's oldest tortoise still randy at 191 years old

Western Santa Cruz Galápagos tortoises are a subspecies of Galápagos tortoises. These giant tortoises are the largest tortoise species on Earth. Males are usually larger than females and grow up to around 1.8 meters (6 feet) long, tipping the scales at about 570 pounds (260 kilograms), according to the San Diego Zoo Wildlife Alliance.

Human activity on the Galápagos has killed off several of its tortoise species and brought western Santa Cruz Galápagos tortoises to the brink of extinction. Historically, sailors reduced tortoise numbers by hunting them for meat. People have also disrupted their habitat and introduced invasive species such as goats, which compete with tortoises for food, and predators like cats and rats, which prey on young tortoises and their eggs, according to the International Union for Conservation of Nature Red List.

Mommy is part of a captive breeding program in U.S. zoos to help safeguard this tortoise subspecies. She finally reproduced for the first time with a male named Abrazzo — who is also around 100 years old. Abrazzo moved to Philadelphia in 2020 after previously living at the Riverbanks Zoo and Garden in South Carolina, which successfully bred western Santa Cruz Galápagos tortoises in 2019, according to the statement.

Tortoises and other reptiles usually remain capable of reproduction throughout their lives after reaching maturity, so they can keep breeding long into old age. Researchers aren't sure how long Galápagos tortoises can live, but one individual was recorded reaching the age of 171, according to the San Diego Zoo Wildlife Alliance.

After mating, Mommy laid 16 eggs in November 2024. Keepers took the eggs and placed them in an artificial incubator. Like most tortoises and turtles, the sex of hatchling Galápagos tortoises is determined by the temperature at which eggs are incubated. Temperatures below 82.4 degrees Fahrenheit (28 degrees Celsius) produce males, while temperatures above 85.1 F (29.5 C) produce females. The keepers incubated half of the eggs at the male temperature and half at the female temperature to get a mix, but only female eggs have hatched so far, according to the statement.

Ashley Ortega, who coordinates the captive Galápagos tortoise Species Survival Plan at Gladys Porter Zoo in Texas, said in the statement that the program was "thrilled" to help welcome the hatchlings and noted that Mommy becoming the oldest first-time producing female of her species made the feat even more incredible.

"Prior to the hatchlings, there were only 44 individual Western Santa Cruz Giant tortoises in all U.S. zoos combined, so these newest additions represent a new genetic lineage and some much-needed help to the species' population," Ortega said. "We are excited to learn more about how we can replicate this success at other accredited zoos since the team in Philly has accomplished something that was seemingly impossible."

Snakes are limbless reptiles that are found on every continent except Antarctica, having adapted to a wide range of environments. They are amazing creatures with some jaw-dropping abilities, and they play a critical role in many food webs.

While most snakes are completely harmless, some inspire dread for good reason. Globally, 5.4 million people are bitten by snakes every year, resulting in between 80,000 and 140,000 annual deaths, according to the World Health Organization.

Of the 4,000 snake species in the world, only about 600 are venomous, though not all of those pose a threat to humans. That doesn't stop some people from developing ophidiophobia, or an intense fear of snakes, which is one of the most common phobias.

Without further ado, how much do you know about snakes?

Remember to log in to put your name on the leaderboard; hints are available if you click the yellow button, and let us know your score in the comments. Good luck!

More science quizzes

—Crocodile quiz: Test your knowledge on the prehistoric predators

—Animal quiz: Test yourself on these fun animal trivia questions

—Shark quiz: How much do you know about these iconic ocean superstars?

Around 34 million years ago, iguanas undertook the longest-known transoceanic trip of any terrestrial species, sailing one-fifth of the way around the world from North America to set up home in Fiji, a new study suggests.

Researchers believe the iguanas made the more than 5,000 mile (8,000 kilometer) journey on rafts made of vegetation, arriving in Fiji shortly after the islands formed. "You could imagine some kind of cyclone knocking over trees where there were a bunch of iguanas and maybe their eggs, and then they caught the ocean currents and rafted over," lead author Simon Scarpetta, lead author and assistant professor of environmental science at the University of San Francisco, said in a statement.

Fiji's bright-green lizards are the only iguanas outside the Western Hemisphere, and how they got there has been a long-standing mystery. In a new genetic analysis published Monday (March 17) in the journal PNAS, researchers found Fiji's iguanas are much more closely related to their Western Hemisphere cousins than previously believed, making the journey directly from the West Coast of the United States to Fiji about 34 million years ago.

"That they reached Fiji directly from North America seems crazy," study co-author Jimmy McGuire, professor of biology at the University of California, Berkeley, said in a statement. "But alternative models involving colonization from adjacent land areas don't really work for the time frame, since we know that they arrived in Fiji within the last 34 million years or so."

Related: Labord's chameleon — the color-changing lizard that drops dead in 4 months

Previously, some biologists posited the Fijian lizards — which comprise the genus Brachylophus — descended from a now-extinct family of iguanas that once populated the Pacific. Others have suggested the lizards could have floated shorter distances from South America and through Antarctica or Australia before finally ending up in the Pacific.

But these ideas were based on past genetic analyses that did not conclusively show how closely Fiji iguanas were related to other iguanids.

The new analysis relies on a genome-wide DNA sequence that Scarpetta collected from over 200 iguana specimens from museums around the world.

The work revealed the Brachylophus genus in Fiji is most closely related to lizards in the Diposaurus genus, which are widespread in the deserts of North America. These desert iguanas are well adapted to searing heat, so potentially had adaptations to survive the long journey.

"Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one," Scarpetta said.

The researchers estimate these lineages split approximately 34 million years ago — roughly aligning with geological history of the islands' formation. "This suggests that as soon as land appeared where Fiji now resides, these iguanas may have colonized it. Regardless of the actual timing of dispersal, the event itself was spectacular," Scarpetta said.

In a first-of-its-kind discovery, a death adder has been found with three super-sharp, venomous fangs, instead of the usual two.

"This is something we've never seen before," Billy Collett, park manager at the Australian Reptile Park, where the snake lives, said in a statement emailed to Live Science. "We've had this death adder in the venom program for about seven years, but only recently did we notice the third fang. I thought it would just shed off over time, but one year later, and it's still there!"

This third fang, located right next to one of the other fangs at the left side of the snake's mouth, also produces venom. This means it has a much larger venom output per bite than is usual for a death adder, making it even more deadly.

This ultra-rare snake "might actually be the most dangerous death adder in the world," Collett said in a video interview. According to the statement, the extra fang is the result of a never-before-seen mutation.

Related: 'Truly primal': Watch Burmese python swallow deer whole in Florida Everglades by stretching its mouth to the absolute limit

Death adders (Acanthophis) are a group of venomous snakes native to Australia and New Guinea. They have one of the fastest strikes of any snake, with some species being capable of biting and injecting venom from their fangs in under 0.15 seconds. Their venom contains neurotoxins that can cause paralysis and even death if left untreated. Before the development of antivenom, around 50% of death adder bites were fatal.

This snake is part of Australian Reptile Park's antivenom production program, and its extremely rare extra fang was discovered when it was being milked for its venom. This involves gently squeezing a snake's venom glands while it bites onto a collection container, causing the venom to pour into the vial.

This three-fanged death adder was found to produce far more venom than usual, with "massive yields" coming out of all three fangs. It produces roughly double that of a two-fanged death adder — although it's unclear whether the higher yield is the result of the extra fang, or that this individual just produces high quantities of venom.

This is the first three-fanged snake ever discovered at the Australian Reptile Park, which has been operating for 20 years and has milked hundreds of thousands of snakes, a spokesperson for the park told Live Science in an email.

"There have been other 3 fanged snakes found in Australia, but from what we can find, there have been no 3 fanged death adders recorded," they said.

Exactly why this snake has three fangs instead of two is unclear, but may be related to the process of fang replacement. Similar to human adult teeth, death adders have replacement fangs growing behind the active ones, so when a fang is lost, a new one moves forward to take its place. This ensures that their fangs remain sharp and functional for injecting venom.

"It's normal for death adders to shed fangs over time and replace them with new ones every few months or so," the spokesperson said. "Unfortunately, we don't actually know what has caused the 3rd fang to develop and don't currently have the facilities to run any tests."

There are about 4,000 different snake species in the world today. They occupy a wide range of habitats — some dwell underground while others live high in the canopies of trees, and many spend their entire lives on the ground. Some even spend a significant portion of their lives underwater. They have adapted to climates ranging from tropical rainforests and deserts to marine environments and the freezing Arctic.

These legless reptiles evolved from four-legged lizards during the Jurassic period (201 million to 145 million years ago). Like nearly all living reptiles, snakes are cold-blooded, meaning they rely on the environment to regulate the temperature of their bodies. As a result, snakes are frequently seen warming themselves in the sun.

Though snakes are often thought to be dangerous, only around 600 species are venomous, about a third of which possess venom that is fatal to humans, according to National Geographic. Even these species are inclined to avoid humans and only strike when threatened. Most snakes are entirely harmless, and they are all crucial predators that help maintain food webs.

4 fast facts about snakes

• Snakes smell by flicking their forked tongues and picking up odors that are transported to special organs on the roofs of their mouths.
• Snakes do not have eyelids. Each eye is covered by a clear membrane that is periodically shed along with the skin.
• Some species of snake have the remnants of legs in the region where their lizard ancestors would have had legs.
• All snakes shed their skin. They do this to grow and remove parasites.

Everything you need to know about snakes

Snake pictures

Discover more about snakes

—13 of the most venomous snakes on the planet

—Do snakes have ears?

—What's the biggest animal that a snake can swallow?

Climate change may be pushing crocodiles to their limit, a new study finds.

In Australia, estuarine crocodiles (Crocodylus porosus) are struggling due to global warming. Like most reptiles, crocodiles are ectothermic (cold-blooded), which means their body temperatures are determined by the external environment rather than by internal processes — in contrast to endothermic (warm-blooded) animals, such as birds and mammals.

When crocodiles need to warm up, they lie in the sun. And when they need to cool down, they may lie in the shade, retreat to cool streams and pools, or bask on the shore at night.

But a warming climate has increased these crocs' body temperatures, which in turn appears to be changing their behavior. In a paper published Feb. 12 in the journal Current Biology, scientists report that over a 15-year period, the average body temperature of the crocodiles increased by a small but significant amount. Further, they spent more days at their critical thermal limit — 89.6 degrees Fahrenheit (32 degrees Celsius).

Previous research on captive crocodiles has shown that body temperatures of 89.6 F or higher lead to reduced swimming and diving performance. When their bodies get too hot, crocodiles spend more time attempting to cool themselves and reduce their activity.

"A hotter croc has a higher metabolism," lead author Kaitlin Barham, a doctoral candidate studying crocodile movement and behavior at the University of Queensland, Australia, told Live Science. "Higher metabolism means burning oxygen more rapidly. Lab research found that they just couldn't hold their breath for as long. It would take them a bit longer to recover at the surface."

Related: Why can't you suffocate by holding your breath?

Between 2008 and 2023, the researchers studied 203 estuarine crocodiles (also called saltwater crocodiles) at the Steve Irwin Wildlife Reserve in Queensland. They tracked the reptiles' body temperatures using acoustic devices implanted under the skin. These devices sent signals to nearby receivers and additional trackers were used to monitor when the crocodiles submerged themselves, and for how long.

If a crocodile was not detected for a period ranging from 30 minutes to 24 hours and then was detected again with a higher or lower body temperature, the scientists assumed that the croc had altered its behavior to regulate its body temperature — either basking in the sun to raise it or finding a cool spot to lower it.

"The croc would disappear for a few hours, and then come back 1 or 2 degrees [C, or 1.8 to 3.6 F] cooler," Barham said.

During the study period, the researchers recorded nearly 6.5 million temperature readings from the crocodiles. The highest body temperatures increased by 0.99 F (0.55 C). Of the crocodiles that were monitored, 135 showed body temperatures exceeding 89.6 F at least once, and one individual showed body temperatures above 89.6 F for more than a month in 2021.

The highest body temperatures were linked to El Niño periods, during which unusually warm Pacific currents led to hot, dry spells on land. The frequency of these periods is believed to be increasing as a result of climate change.

Cooling behaviors were detected more frequently when ambient temperatures were hotter. The crocodiles also submerged themselves for shorter periods when temperatures were high, according to the tracking data.

It is unclear how these alterations to the crocodiles' behavior are affecting their survival. They are certainly adapted to high temperatures already, but it is possible that increasing periods of hot weather may reduce their ability to hunt. Crocodiles are stealth predators and usually submerge themselves to ambush prey on the shores of rivers.

"Every minute that they're up on the bank trying to bring their body temperature down is a minute that they're not spending traveling, reproducing or looking for food," Barham said. "That could result in future indirect effects on their health."

Crocodile quiz: Test your knowledge on the prehistoric predators

Name: Labord's chameleon (Furcifer labordi)

Where it lives: Western Madagascar

What it eats: Crickets, flies, locusts, grasshoppers and stick insects

Why it's awesome: Labord's chameleons live fast and die young. They hold the record for the shortest lifespan of all tetrapods — they hatch, grow, mate and die in just four to five months.

Labord's chameleons actually spend more time developing inside their eggs than they do outside of them. For around eight to nine months, the embryos rest beneath the forest floor, preparing for their whirlwind time above ground.

These short-lived chameleons grow to around 3.5 inches (9 centimeters) long and are found exclusively in forests in the lowlands of western Madagascar.

Once they hatch, they grow quickly and reach sexual maturity at 2 months old.

Their aggressive mating season begins in January, during the wet season, with males battling fiercely for the chance at reproducing then dying shortly after.

Females then put all their energy into producing eggs, which they lay in February. They have a relatively high reproductive rate to compensate for their short adult lifespan, with each female laying up to 11 eggs. Hours after laying their eggs, the females die.

This means that for two-thirds of the year, the entire species exists in eggs buried underground.

This unusual — and seemingly risky — lifecycle is thought to be a survival adaptation to the harsh seasonal environment of western Madagascar. The region experiences distinct wet and dry seasons, with the rainy season providing the necessary resources for survival, such as food and water, while these become more scarce in the dry season. Although many tropical regions experience wet and dry seasons, the climate of Madagascar is extremely variable and environmental unpredictability is much greater than other tropical areas.

To align with these conditions, the chameleons have evolved to spend most of the year as embryos in their eggs — emerging during the brief rainy season to mate and lay more eggs.

By compressing their entire adult existence into the wet season, the chameleons maximize their chances of finding food and mates. This strategy also reduces competition for resources, as most adults die before the next generation hatches (although during unusually long rainy seasons, females can survive for a second breeding season).

Chameleons are known for their ability to change color, and Labord's chameleons are no different. Their skin changes color by expanding and contracting special cells that contain nanocrystals, which alters how they reflect light. But they don't do it to camouflage themselves. Instead, they use it to communicate with other chameleons — for example, to attract mates — and in response to emotions.

In a 2024 PBS documentary filmed in the Kirindy Forest in western Madagascar, a Labord's chameleon broke into a vibrant, pulsating display of color just moments before its death. This is the result of the nervous systems continuing to send signals to skin cells, resulting in a dramatic "technicolor fireworks display," according to the experts in the documentary.

Anyone who has watched a rooster stalking around a farmyard might agree that there is something very dinosaur-like about birds. That may come as no surprise, given that birds are dinosaurs. But in terms of classification, this raises a question: Since dinosaurs are reptiles, does that mean that birds are reptiles, too?

"I would say that any modern biologist would, or should, say that birds are reptiles," Martin Stervander, an evolutionary biologist and senior curator of birds at National Museums Scotland, told Live Science.

It wasn't always this way. Before the 1940s, biologists relied on a system called the Linnaean method to classify all life on Earth. This approach was developed by Carl Linnaeus in the 1730s, and it works by grouping animals that have similar physical characteristics. Linnaeus determined that all reptiles share two key features: They have scales, and they are ectothermic, or "cold-blooded," meaning they must rely on external sources of heat to regulate their body temperature.

Because warm-blooded, abundantly feathered birds lack these features, "birds were considered their own branch on the tree of life" under the Linnaean system, said Klara Widrig, a postdoctoral fellow in the Vertebrate Zoology Department at the Smithsonian's National Museum of Natural History in Washington, D.C. Linnaean classification accurately describes many relationships and helped to establish the broad branches of the tree of life we use today. Yet this classification system overlooks something that can reveal a lot more about an organism: its genes.

From the 1940s, the ability to examine genetic material gave rise to a new type of classification, called phylogeny. The phylogenetic method groups or separates organisms based on how much of their DNA they have in common. It also allows scientists to compare organisms' DNA to trace their evolutionary history and find shared ancestors.

Phylogeny for birds

Under this system, organisms are grouped into "clades," which are distinct branches on the phylogenetic tree that include all the descendants of a most recent shared ancestor. For example, modern birds are grouped into the Neornithes clade, because they all emerged from a common Neornithine ancestor that emerged 80 million years ago, before the nonavian dinosaurs went extinct. "Clades are a nested hierarchy," Widrig explained. So "if you go further back along the branches of the tree of life, you find that [Neornithes] also belong to the more inclusive clade Theropoda," a group of two-legged and mostly meat-eating dinosaurs that itself is descended from the clade Dinosauria.

Even in the dinosaur age, the defining features of scaly reptiles and birds weren't so distinct. Research suggests that some dinosaurs were warm-blooded and some nonavian dinosaurs sported feathers. Meanwhile, later on we know that birds that looked exactly like modern birds were already stalking the Earth alongside their dinosaur kin 66 million years ago. One of these was the "Wonderchicken" (Asteriornis), a fossil that was described in 2020 by a team that included Widrig. "Say if I got into a time machine and scooped up an Asteriornis and brought it back, everybody would be like, 'Oh yeah, that's just a normal-looking bird.'"

But back to the tree of life: birds' descent from Theropods and Dinosauria is what makes them dinosaurs. Meanwhile, Dinosauria, along with crocodilians, and other lineages like the pterosaurs, are contained within another clade, called Archosauria. This clade, in turn, shares an ancestor with a group called Lepidosauria, which gave rise to all modern lizards, snakes and the tuatara. That shared ancestor was a creature called a sauropsid that emerged about 315 million years ago, and launched the clade by the same name.

Sauropsida was one of two lineages that branched off from the amniotes (vertebrate animals that lay shelled eggs or carry fertilized eggs), the other being the group that evolved into the class Mammalia. Sauropsida, meanwhile, has become synonymous with the class "Reptilia," because within its network of clades upon clades, all reptiles — both living and extinct — are contained.

Related: If birds are dinosaurs, why aren't they cold-blooded?

"All of these guys — snakes and turtles and crocodiles and birds, and the dinosaurs when they were around — they all come back to one common ancestor," Stervander explained, and so under the phylogenetic grouping system, "that simply means that since birds are in [that clade], they are, per definition, reptiles." This is why phylogeny is valuable, because it can reveal that organisms that look very different are, in fact, very close to one another genetically and belong in the same group.

Why don't birds look like other reptiles?

The connections between birds and their scalier kin might have been easier to grasp if there hadn't been a mass extinction event 66 million years ago. "The reason why birds seem so strange compared to the rest of the reptiles that we have alive today is because all the evolutionary intermediate stages are extinct, so we don't have that to compare to," Widrig said. When the asteroid wiped out swathes of life on Earth, it obliterated whole sections of the Archosauria lineage of reptiles, leaving only crocodiles and some avian dinosaurs behind.

Without this void in the once-intricate tree of life, evolution might have ushered relatives into the modern age that would have made birds' reptilian roots more immediately clear. Instead, today crocodiles are birds' closest living relatives, even though they sit far apart on the phylogenetic tree.

To put it into human terms, "if all non-human primates were to suddenly go extinct today, our closest living relatives would actually be rodents and rabbits," Widrig said. They would be closest to us on the remaining branches of the tree of life, and our shared mammalian ancestry might be harder to accept.

If it still seems strange to think of birds as reptiles, it might partly be because of those Linnaean roots, which continue to shape our colloquial understanding of what a reptile is. "It's not until around the [19]40s where genetic evidence actually clarified where birds sit [on the tree of life]," Stervander said. "People had been referring to reptiles for almost two centuries before that. I think that's why there's been some unwillingness to redefine what we call the reptile."

But modern science is changing that, revealing unexpected connections in the tree of life — and opening our eyes to skies filled with modern feathered, flying reptiles.

Name: Cave-dwelling dwarf crocodiles (Osteolaemus tetraspis)

Where it lives: Abanda cave system, Ogooue-Maritime Province, Gabon

What it eats: Cave crickets and bats

Why it's awesome: Deep inside one of Gabon's cave systems lives an unusual population of orange dwarf crocodiles. They live in complete darkness, feast on bats and swim in liquid guano (aka bat poop.)

It's unknown how many crocodiles are living in these caves, or when they adopted this subterranean lifestyle, but they may have been down there for thousands of years — and scientists say they may even be in the process of evolving into a new species.

The cave-dwelling crocodiles were only studied for the first time in 2010, and a 2016 study that compared them to their forest-dwelling counterparts showed a number of differences between the two. Their diets are very different, with the cave crocs feeding almost exclusively on the bounty of crickets and bats that cling to the cave walls. They found the cave crocodiles were generally in better condition than those living in the forest, which the team say is likely due to the abundance of prey available and a lack of predators.

They suggest the cave crocodiles lay their eggs at the mouth of the caves, then the juveniles venture into the darkness. Once they reach adulthood, it's thought they barely leave the caves again.

Orange skin and genetic changes

The unusual orange skin seen on adult crocodiles may be the result of their time swimming in bat guano, which is rich in urea, lead author Matthew Shirley, a conservation biologist from Florida International University, told National Geographic in 2018. Over time, this exposure appears to cause chemical bleaching of the crocodiles' skin, the study authors wrote.

Intriguingly, genetic analysis of the crocodiles — which has not been published — suggests the orange cave crocodiles may be mutating, according to a Guardian article in 2018. Researchers told the newspaper that one haplotype (a group of DNA variants inherited from a parent) found in the cave crocs wasn't present in the forest crocodiles. "The [crocodiles in the] caves of Abanda stand out as an isolated genetic group," study co-author Richard Oslisly, a researcher at France's Institute of Research for Development, told the Guardian.

This genetic change is evidence that the cave crocodiles are evolving into a new species. "As a result of that isolation and the fact that few individuals come in or go out, they're in the process of [becoming] a new species," Shirley told National Geographic. "Whether that happens soon or not is anyone's guess."

Crocodile quiz

Iguanas falling from trees during cold weather has become so common in Florida, it's even been included in weather forecasts. But why do these reptiles react this way to the cold?

Since they're cold-blooded, green iguanas (Iguana iguana) can struggle to maintain their body temperature in colder weather, putting them in a temporary torpor state. This is a type of paralysis that can cause them to lose muscle control — so they fall from their perches. The paralysis typically occurs when the weather dips into the 40s Fahrenheit, said Joe Wasilewski, a conservation biologist at the University of Florida. The cold weather affects other non-native reptiles in Florida too, like pythons and crocodiles, which often can't survive when the temperature drops.

Non-native species

The original native range of green iguanas extends from southern Mexico to central Brazil and Bolivia, so their optimal body temperature is between about 85 and 95 degrees Fahrenheit (29 to 35 degrees Celsius), Wasilewski told Live Science. When the temperature drops below 50 F (10 F), the iguanas' metabolism slows down, and they start falling from trees once the temperature hits the low 40s.

"Their body metabolism is built for living in a tropical area," Wasilewski said. "They've been placed in these habitats, south Florida for instance… where once or twice a year we get a cold snap."

Expanding range

The phenomenon has been more noticeable recently due to booming iguana populations. Iguanas were introduced to Florida in the 1960s, and their populations have grown since the 1990s, partly due to a lack of natural predators.

The falling iguana phenomenon is well known in South Florida because the green iguana population is growing, but also because Florida is likely the northernmost extent of their invasive range, says Wasilewski — so it's one of the few places where iguanas mostly thrive, but sometimes experience cold weather. This might change though, with temperatures warming due to climate change.

"I'm getting more and more reports of counties north of where their northern extent is, starting to see [iguanas]," said Wasilewski. "As the weather gets warmer they're going to distribute themselves to more northern counties; however, those more northern counties are going to have more cold snaps than southern Florida, and I don't think they'll be able to survive."

Typically, paralyzed iguanas will come to their senses as the temperature warms, but the falling iguanas can be a hazard, injuring people or damaging cars. The National Weather Service has issued falling iguana warnings, encouraging people to be aware of their surroundings — and to leave a cold-stunned iguana alone if they come across one.

"Staff with the FWC's Nonnative Fish and Wildlife Program reminds the public that if they encounter a cold stunned iguana, they should not bring it into their homes," Lisa Thompson, a spokesperson for the Florida Fish & Wildlife Conservation Commission, told Live Science in an email. "Iguanas are wild animals and once they recover and warm-up, they could act defensively."

Wasilewski recounted once being called to collect cold-stunned iguanas, transporting them in a box while the weather warmed up, and later opening the box to find it full of extremely active and jumping iguanas.

"If nobody bothers them… chances are, they're gonna warm up and scurry right back up the tree," Wasileski said.

Henry the world's oldest known crocodile is celebrating his 124^th birthday at a conservation center in South Africa today (Dec. 16).

The Nile crocodile (Crocodylus niloticus) has lived at the Crocworld Conservation Centre in Scottburgh, South Africa since 1985. He was originally captured in the Okavango Delta in Botswana in 1903.

Henry, now a vigorous senior resident at the Crocworld Conservation Center, is said to have fathered over 10,000 offspring with numerous partners since he arrived there almost 40 years ago.

While his exact birthday is unknown, Crocworld representatives estimate he was born around 1900 and celebrate his birthday on Dec. 16 each year.

"He's clearly old," Steven Austad, a biologist studying animal aging at the University of Alabama, told Live Science. "Whether he's 100 or 130, we don't really know. An age of 124 is not inconceivable for a crocodile."

Reptiles are known for their impressive longevity. Usually, a good rule of thumb for an animal's lifespan is to look at their size — smaller animals typically live shorter lives because they have higher metabolisms, meaning that they burn more energy and age more rapidly as a result.

But even compared with other animals of roughly the same size, reptiles tend to be much longer-lived. Austad said that being cold-blooded allows them to conserve energy by relying on external heat sources to regulate their body temperature.

"A crocodile that was the same size as a person would only need to eat about 4% as much as a mammal like us," he said.

Crocodiles, like some other reptile species, continue growing with age. Henry weighs 1,540 pounds (700 kilograms) and measures 16.4 feet (5 metres), which is on the larger end for his kind. Their huge size keeps them safe from potential predators in their old age.

Related: Scientists to read Cassius the giant crocodile's bones to find out exactly how old he was when he died

Henry's life in captivity has also likely helped him reach such an old age, keeping him well fed and safe from accidents and disease.

"Animals that for whatever reason, happen to live in a safe environment, tend to live longer," Austad said.

Reptiles, compared to many other vertebrates, also do not show signs of noticeable decline in physiological abilities as they age.

Other biological traits may also contribute to Henry's longevity. Theories posit that proteins found in the blood of Nile crocodiles may have antibacterial properties and help them fight off infections and disease. Similarly, some researchers claim that their gut microbiomes could contribute to their robust immune system.

Studying the aging of crocodiles like Henry can be challenging since researchers have to catch them in their infancy, tag them, then follow them throughout their lives. Because of this, many theories around the secrets to reptilian aging are speculative, like the role of their immune system and microbiome, Austad said. "[Crocodiles] live longer than the careers of the scientist studying them," he said.

Name: Cantor's giant softshell turtle (Pelochelys cantorii)

Where it lives: Rivers in South and Southeast Asia

What it eats: Fish, crustaceans, mollusks, frogs, insects, birds, small mammals

Why it's awesome: Cantor's giant softshell turtles — named in honor of Danish zoologist Theodore Edward Cantor — spend 95% of their lives completely motionless, buried under mud or sand in shallow rivers with only their eyes and snorkel-like snouts protruding out. But when these unusual-looking reptiles spot something to eat, they can move at lightning-quick speeds.

When they spot fish, frogs or crustaceans, they rapidly extend their necks to strike their prey. They have long claws and powerful jaws that are strong enough to crush bone.

Unlike their hard-shelled cousins, these turtles have leathery, flat, green or brown shells. These large, freshwater turtles are also known as "frog-faced softshells" because of their amphibian-like facial features. They can grow up to 40 inches (100 centimeters) long — although some sources suggest they can grow even larger — and weigh more than 100 kilograms.

Like other soft-shell turtle species, they are thought to have the ability to extract oxygen from the water through their skin, which helps them stay underwater for long periods of time. However, they can only get so much oxygen this way, so they come up to the surface to breathe air twice a day.

These endangered turtles are extremely rare: Between 1985 and 1995, only a single specimen was found. They are native to rivers in India, Bangladesh, Burma, Thailand, Malaysia, Laos, Cambodia, Vietnam, China, the Philippines and Indonesia.

In 2024, the first nesting site of a Cantor was discovered by biologists on the banks of the Chandragiri River in Kerala,India. The researchers used knowledge from local communities to locate the turtle.

Name: Gharial (Gavialis gangeticus)

Where it lives: Freshwater rivers in India and Nepal

What it eats: Fish. Juveniles also eat insects, frogs and crustaceans.

Why it's awesome: The gharial is known for its long, skinny snout, which looks like it got slammed in a door.

An adult male has a "ghara" at the end of its snout: a lightbulb-shaped bump, named after a bulbous Indian pot. This bizarre lump looks attractive to females and helps males woo their mates by blowing bubbles and creating a strange love song.

This ghara "partially covers the crocodile's nostrils and acts as a vocal resonator, creating a loud, buzzing sound when the gharial vocalizes," according to Smithsonian’s National Zoo and Conservation Biology Institute.

If these crocodilian pickup lines are successful and the male attracts a female — or several, as gharials are polygamous — the pair mate. This usually happens in December or January. In March or April, when the dry season arrives, females dig nests and lay around 40 eggs.

Related: Low-flying helicopter sparks massive crocodile orgy in Australia

These large eggs are the biggest of all crocodilian eggs. Weighing up to 6 ounces (170 grams), they're about the same weight as a hockey puck. Once fully grown, adults can reach 15 feet (4.5 meters) and, on average, weigh around 350 pounds (160 kilograms).

"As with all crocodilians, the sex of the hatchlings is determined during incubation," according to Smithsonian. Incubation can take between 60 and 80 days. Babies stay with their mother for several weeks, or sometimes months, after hatching.

Although they look like crocodiles or alligators, gharials split off from other crocodilian species over 40 million years ago.

Unlike crocs and gators, gharials don't ambush their prey. Instead, swiping their snout from left to right allows them to detect vibrations in the water. Using this method, they find nearby fish and chomp on them with their interlocking teeth.

These animals are well-adapted to watery habitats but can’t move well on land because their leg muscles are too weak, so they slide on their bellies to get around above water.

Gharials were once plentiful between Pakistan and Myanmar, with an estimated 5,000 to 10,000 individuals in the wild in the 1940s. They are now critically endangered as a result of hunting, fishing and habitat loss, with around 650 mature individuals left. Captive breeding, nest monitoring and other conservation activities helped boost this number from around 250 in 2006.

The mighty king cobra — the world's longest venomous snake — is actually four distinct species, scientists have confirmed in a new study.

For 188 years, the king cobra has been represented by a single species, Ophiophagus hannah. But this widely distributed species shows huge differences in body coloration and other physical characteristics across different regions, leading scientists to question whether it is a single species.

In a study published in 2021, scientists confirmed genetic differences among king cobra populations. Building on this research, scientists have now compared physical differences in museum specimens and identified four separate species: the Northern king cobra (O. hannah), the Sunda king cobra (Ophiophagus bungarus), the Western Ghats king cobra (Ophiophagus kaalinga) and the Luzon king cobra (Ophiophagus salvatana). The findings were published Oct. 16 in the European Journal of Taxonomy.

"I feel like we created history," study author Gowri Shankar Pogiri, founder of the Kalinga Foundation and director of the Kalinga Centre for Rainforest Ecology, told Mongabay.

Related: Evolution of snakes takes surprise twist — cobras didn't come from where we thought they did

King cobras live in humid environments, including open forests and dense mangrove swamps, from northern India to southern China and throughout Southeast Asia. Across these regions, their appearance varies in body color, pattern and size.

In the 2021 study, a DNA analysis that accounted for almost the entire distribution range of king cobras identified four distinct genetic lineages. These lineages were classified as confirmed candidate species — species yet to be formally described and named.

Building on this research, the new study looked at the physical differences among 153 museum specimens. An analysis of the specimens' body morphology — including their color patterns, body widths and dental characteristics led the researchers to identify four species corresponding to the genetic lineages found in the 2021 study.

The Northern king cobra (O. hannah) is widespread across the sub-Himalayas, eastern India, Myanmar and Indochina, and extends southward to the narrowest part of peninsular Thailand, in Kra Isthmus. Adults have dark-edged yellow bands and between 18 and 21 teeth.

The Sunda king cobra (O. bungarus) lives in the Malay Peninsula and the islands of the Greater Sundas — including Sumatra, Borneo and Java — as well as in Mindoro in the Philippines. Large individuals of this species are usually unbanded or have narrow, pale bands with dark edges along the body.

The Western Ghats king cobra (O. kaalinga) is restricted to the Western Ghats of the Indian Peninsula. This species differs from O. bungarus in that it does not have dark edges around the pale bands along its body.

Like O. kaalinga, the Luzon king cobra (O. salvatana) inhabits Luzon, an island in the northern Philippines. It has extremely angular pale body bands compared with the bands of the three other species.

All of these species are venomous. King cobras are amongst the most venomous snakes in the world and release a large dose of venom in a single bite that can kill a human in as little as 15 minutes. The new study shares that this could be the first step in developing improved antivenom from Ophiophagus bites in their respective regions.

Pogiri believes there may be more unknown king cobra species yet to be discovered on small islands that were not part of this research. "Studying them is already underway," he said.

Crocodiles are among the world's most impressive, deadly predators. They are masters of camouflage, waiting patiently for unsuspecting prey to approach before lunging at high speeds. They have thick, rigid skin and dozens of sharp teeth inside jaws that deliver some of the biggest bite forces of any living animal. Other than humans, adult crocs have no natural predators.

They've existed for millions of years, now inhabiting five of Earth's seven continents.

But how much do you know about crocodiles? Take our science quiz to find out.

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Scientists in Australia may soon learn exactly how old the giant crocodile Cassius was when he died after performing a necropsy on the record-breaking predator.

Cassius, who was the world's largest living captive crocodile, died in Australia this month after 40 years in captivity. Experts estimated the gigantic saltwater croc (Crocodylus porosus) could have been over 120 years old — but they don't know for sure.

Sally Isberg, founder of the Centre for Crocodile Research in Australia’s Northern Territory, told ABC News that "all indications at this stage indicate that he has died of [old age]."

But further tests following the animal autopsy, which will be carried out imminently, may also reveal the 17 feet and 11.75 inch (5.5 meters) croc's exact age, something that even his keepers — who made up his birthday — had never been sure of.

When Cassius was captured in the Finniss River, near Darwin, in 1984, researchers believed he may have been up to 80 years old. But once crocodiles fully mature, their growth rates slow down, making it impossible to determine his exact age.

"There is no way of knowing Cassius' actual age as he was born in the wild and the age is just an estimate," Toody Scott, one of Cassius' keepers at Marineland Crocodile Park, previously told Live Science.

Related: World's largest captive croc turns 120, giving scientists 'serious knowledge on longevity'

The only way to find out the animal's age involves cutting into its bones to count the growth rings, which can only be done after death. Scientists plan to cut into Cassius' back and right femur bone to take samples that will be sent away for testing.

"My plan is to send it to a lab that can cross-section it and look for growth rings, just like in trees," Isberg told ABC News. However, it could take months before the results are back and the process isn't guaranteed to work, she added. "I'm a little bit concerned that those growth rings might not be quite as easily discernible."

Grahame Webb, a zoologist and leading crocodile researcher, helped capture Cassius from the wild in 1984 after the aggressive croc started attacking cattle and boat propellers. He told ABC News that counting growth rings might not give an accurate age estimate. "These animals stop growing and they can live for decades afterwards without growing," he said.

Cassius measured just under 18 feet (5.5 m) long when he died. However, he was also missing part of his snout and the end of his tail. Without these battle scars, Webb believes the crocodile would have reached a total length of 19 feet (5.8 m).

Cassius, the world's largest captive crocodile, has died in Australia after his health started declining in mid-October.

"It is with deep sadness that we share the passing of our beloved mate Cassius," Marineland Melanesia Crocodile Habitat & Gift Shop wrote in a Facebook post announcing his death. "He was more than just a Crocodile, he was a cherished member of our family and brought joy and companionship to his best mate George for over 37 years."

The saltwater crocodile (Crocodylus porosus) — who was 17 feet and 11.75 inches (5.48 meters) long — received the Guinness World Record as the largest living captive crocodile in 2011. But, as no one measured him since, he could have grown even bigger. The species can grow up to 23 ft (7 m) long.

Cassius had lived at Marineland Melanesia Crocodile Habitat on Australia's Green Island since 1987. He was captured in the Finniss River, near Darwin, in 1984 because he was acting aggressively and causing problems.

"As an apex predator, this big crocodile was getting into all sorts of trouble, from catching and eating cattle to attacking boat propellers," Marineland Melanesia's representatives wrote on its website. "It is believed this is where and how he sustained his many battle scars, including losing his front left leg, part of his snout and around 15 cm [6 in] off the end of his tail."

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Cassius was moved to an "assisted care residence" in Cairns on Oct. 5 and his health started declining shortly after. He died on Nov. 2. "He was very old and believed to be living beyond the years of a wild croc," according to Marineland Melanesia's post.

Although experts aren't sure, they think this massive croc may have been over 120 years old when he died. When he was caught, Cassius was estimated to be between 30 and 80 years old. Crocodile growth rates slow significantly once they reach adulthood.

"There is no way of knowing Cassius' actual age as he was born in the wild and the age is just an estimate," Toody Scott, one of Cassius' keepers at Marineland Crocodile Park, previously told Live Science, adding that his birthday "was essentially made up."

Despite his enormous size, Cassius wasn't the largest crocodile ever kept in captivity. This record goes to a saltwater crocodile named Lolong, who was caught in the Philippines in September 2011, and measured over 20 ft (6.17 m) before his death in 2013.

A huge Burmese python has been found swallowing a deer whole in Florida's Everglades. The impressive feat challenges what gape models suggest the invasive snakes are physically capable of.

"It felt like we were literally catching the serial killer in the act and it was intense to observe [in] real time," Ian Bartoszek, a wildlife biologist and science coordinator at the conservation organization Conservancy of Southwest Florida, told Live Science in an email.

The female Burmese python (Python bivittatus) measured 14.8 feet (4.5 meters) long and weighed 115 pounds (52 kilograms). It was discovered feasting on a white-tailed deer (Odocoileus virginianus) that weighed 76.9 pounds (35 kg) — almost 67% of the snake's mass. To devour the deer, the snake's mouth stretched so wide it reached 93% of its maximum gape, according to a study published Aug. 22 in the journal Reptiles & Amphibians.

"This was the most intense and impressive sight we have observed in 12 years of tracking pythons in southwestern Florida," Bartoszek, one of the study authors, said. "It was truly primal and felt like a scene that had been playing out for millions of years wherever you have large snakes. Unfortunately our native wildlife in Florida have not evolved with this apex predator and you are seeing that result with these images."

Related: The biggest snake in the world (and 10 other giant serpents)

Burmese pythons are an invasive species in the Everglades and were introduced at some point in the mid to late 20th century. The first sighting was in 1979, and by the 1990s they had gained a stronghold, feasting on native species while having no natural predators to control their population. While the current population size is unknown, experts estimate there could be hundreds of thousands in Florida. Over the last few decades, Burmese pythons have decimated local ecosystems, wiping out several mammal species.

Burmese pythons are known to eat deer and even alligators, but finding the predators in the act is challenging, limiting how much scientists know about what these apex predators are capable of eating, and therefore how much of an impact they're having on the ecosystem.

Related: Which animal has the stretchiest mouth?

According to the study, the previously assumed maximum gape for a Burmese python (the width it can open its jaws) was around 8.6 inches (22 centimeters). However, the researchers examined three of these snakes — including the 14.8 foot python — and found they had a maximum gape of 10.2 inches (26 cm). The discovery has "significantly affected" models showing what Burmese pythons are physically capable of swallowing, the researchers wrote.

"These observations and this study serves as another warning sign to the threat imposed on the Everglades ecosystem by the Burmese python," Bartoszek said.

Burmese pythons can swallow huge prey because their jaws aren't fused at the front, which enables them to stretch far wider than similar-sized snake species. "Our anatomical measurements indicate this deer was very near the size limit on the prey that could be consumed by this snake," study author Bruce Jayne, professor of biological sciences at the University of Cincinnati, said in a statement emailed to Live Science. "Hence, these snakes resemble overachievers by sometimes testing the limits of what their anatomy allows rather than being slackers that eat only 'snack size' prey."

The deer-eating snake was located with the help of a male python called Ronin. Ronin is fitted with a tracking device that leads researchers to females — part of a program that releases males as "scout snakes" during the breeding season. Burmese pythons are prolific breeders, with each female able to produce dozens of eggs each season. Removing females is a way of controlling the population.

"Each breeding season [Ronin] leads us to multiple females that we humanely remove before they have a chance to lay eggs," Bartoszek said. "All of the pythons we remove are humanely euthanized. We have a lot of respect for the Burmese python and they are here through no fault of their own. However we understand the impact they are having on native wildlife and are not sitting on the sidelines."

Name: Greater short-horned lizard (Phrynosoma hernandesi)

Where they live: North and Central America

What they eat: Ants, spiders and other small insects

Why they're awesome: Greater short-horned lizards have a squat, flat shape and short snouts, which makes them look more like amphibians than reptiles — hence the nickname "horny toads." But these lizards are most famous for their unusual defense mechanism: When threatened, they squirt a stream of blood from their eyes up to a distance of 5 feet (1.5 meters).

They do this by restricting the blood flow leaving their heads, which increases blood pressure and causes tiny blood vessels to burst around the eyes. They shoot the blood at predators to cause confusion, giving them a chance to escape.

Around eight species of horned lizards are thought to use this grisly trick, known as autohaemorrhaging.

Greater short-horned lizards, which grow to around 6 inches (15 centimeters) long, may release a third of theirits total blood supply this way.

While it doesn't appear to deter birds, the blood does affect canines like dogs (Canis familiaris), coyotes (Canis latrans) and foxes (Vulpes), which shake their heads to get rid of it. The lizards seem to recognize this and are more likely to use it on dogs than on other predators.

The blood is laced with toxic chemicals, which may come from the venomous harvester ants (Pogonomyrmex) that the lizards eat. Although their blood isn’t poisonous, it tastes unpleasant to predators. Short-horned lizards aren't affected by the venom of the harvester ants they feed on because a chemical in their blood plasma neutralizes it. They also produce large amounts of mucus to immobilize the insects, enabling the lizards to swallow them without getting hurt by the venom.

But blood squirting isn't short-horned lizards' only defense. They have mottled skin and flat bodies, making them very well-camouflaged. Their bodies are covered in sharp spines, including two large head spikes. If a predator attempts to bite them, the feisty lizards bow their head, exposing the horns to the predator's mouth.

The lizards can also inflate themselves to twice their normal size when attacked. Not only does this make them look more intimidating, it can cause predators trying to swallow them to choke.

Scuba-diving lizards have an aquatic trick up their sleeves: They can create air bubbles on their foreheads to breathe underwater, enabling them to stay submerged for long periods and escape predators, researchers say.

In 2018, scientists captured the first-ever footage of a semi-aquatic lizard known as a stream anole (Anolis oxylophus) breathing underwater using a bubble of stored oxygen surrounding its snout — an ability that had never been seen before in lizards. Since then, at least 18 other species of anoles have been found to do this too, including water anoles (Anolis aquaticus).

However, until now, researchers had no idea if this bubble enabled these lizards to stay underwater for a long time or if it merely formed as a side effect of their water-repelling skin.

In a study published Sept. 18 in the journal Biology Letters, researchers tested nearly 30 water anoles and found that those using air bubbles stayed underwater 32% longer than anoles without bubbles. In the wild, this extra time underwater likely helps them to evade predators.

"There are a lot of threats in their environment, and it makes sense that they would evolve a unique way of dealing with them using the resource — water — that they have available," study author Lindsey Swierk, assistant research professor in biological sciences at Binghamton University in New York, told Live Science in an email.

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Semi-aquatic water anoles spend most of their time living on boulders close to river banks in forests in Costa Rica and Panama. They are small lizards that can grow up to 8 inches (20 centimeters) long. When threatened, they have been observed jumping into nearby water to escape.

"We know that they can stay underwater at least about 20 minutes, but probably longer," Swierk said.

Upon diving, these anoles exhale to create a bubble that surrounds their head, held on by the lizards' water-repelling skin. "When water anoles dive, their hydrophobic ("water-repelling") skin keeps a slick of air over the body surface," Swierk said.

As the anoles exhale and inhale, the bubble expands and collapses. The researchers suggest this redistributes air on and in an anole's body, giving it sufficient oxygen for long dives.

To test this, scientists collected 28 water anoles from the Rio Java in Costa Rica. The team applied a substance to 13 of the anoles' heads to stop their skin from being water repellant, meaning the bubble would fail to attach, Swierk said.

"We then compared the dive length and the ability to rebreathe bubbles in anoles with and without emollient applied," Swierk said.

In the control group — the anoles with no substance applied — the longest dive recorded was 477 seconds (nearly eight minutes), although this was excluded from the analysis for being an outlier. The longest dive included in the analysis was 308 seconds (just over five minutes). In the group with the substance applied, the longest dive was 254 seconds (over four minutes).

On average, anoles without the substance applied spent 67.5 seconds longer underwater than those with the substance. "These results show that when semi-aquatic anoles are allowed to rebreathe using bubbles, they can dive longer," Swierk said.

Swierk suggests the difference between dive times may have been greatly different if this experiment was conducted in the wild and not in tanks. "The pressure to stay concealed from a real predator, which we didn't use in our study, could nudge the control group's dive times much longer," Swierk said.

Anoles are not the only animals known to use bubbles underwater. For example, diving beetles carry trapped air behind them at the tip of their wing covers. This bubble acts as a "physical gill," exchanging oxygen with the water to replenish the supply inside the bubble.

The team now wants to find out if water anoles use their breathing bubbles in the same way.

When wildlife officials in Georgia stumbled upon a pair of seemingly lifeless snakes that had been vomited up by another, larger snake, they were already surprised by what they had found. But things took an even weirder twist when one of the regurgitated serpents suddenly woke up and slithered off.

Wildlife technicians from Georgia's Department of Natural Resources (DNR) came across the unusual scene in November 2023 while surveying federally protected eastern indigo snakes (Drymarchon couperi) in southern Georgia, according to a DNR Facebook post written on Aug. 29.

The team found a live 4-foot-long (1.2 meters) indigo snake alongside two other snakes — a "young rat snake" and a juvenile eastern diamondback rattlesnake (Crotalus adamanteus) — that had both "clearly [been] swallowed and then expelled" by the larger snake, DNR representatives wrote.

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While the rat snake did not survive being eaten, the regurgitated rattlesnake eventually showed signs of life around an hour after it was found, and it didn't seem to be particularly bothered by the ordeal. "It was later seen basking in the sun instead of taking shelter in a burrow," DNR representatives wrote.

If that wasn't odd enough, the wildlife experts soon realized that the rattlesnake also had a large bulge in its midsection, suggesting it had recently swallowed a mouse whole.

"This unusual episode not only reveals the indigo's impressive hunting abilities but also the rattlesnake's unexpected resilience," DNR representatives wrote.

Snakes eating one another whole is nothing new, and the size of the meal is rarely an obstacle.

For example, in June 2022, a Georgia resident filmed an eastern kingsnake (Lampropeltis getula) slowly eating a much larger timber rattlesnake (Crotalus horridus). A study released in August this year also documented an incident where a Burmese python (Python bivittatus) swallowed a larger reticulated python (Malayopython reticulatus) from the tail up.

However, eating such massive prey also comes with risks, such as choking.

In February 2022, a rim rock crowned snake (Tantilla oolitica) was found dead in Florida after choking on a centipede, which was still lodged in its mouth when it was discovered. And in September last year, a herpetologist in France stepped in to save a viperine snake (Natrix maura) that was choking on an invasive fish.

In the recent case, the indigo snake may have been trying to avoid a similar fate when it expelled its two victims. However, it is also possible that it voluntarily surrendered its meal to escape a predator or because it was stressed out by the nearby wildlife experts looking for it.

Name: Thorny devil (Moloch horridus)

Where it lives: Australia

What it eats: Ants

Why it's awesome: Thorny devils are native to Australia and live in the country's arid scrubland and interior desert. These small lizards grow to 8 inches (20 centimeters) long and have evolved an impressive set of defenses, including an appendage on the back of the necks that acts as a "'false head."

When threatened, the lizards tuck their real head down between their front legs, leaving the fake head exposed while protecting the real head.

These lizards' defenses don't stop there. Their bodies are covered in spikes, which are the size of rose thorns and are thought to deter predators by making the lizards difficult to capture, bite and swallow.

Thorny devils can also inflate their chests to make themselves look larger when faced with a threat. When they're out in the open — either looking for food or mates — they also have a slow and jerky walk, which is thought to confuse predators. This is because moving slowly and intermittently may help the lizards from activating a predator’s chase-and-attack response, which can happen when they spot quick-fleeing prey.

Devils are well-adapted to their hot, harsh environment. In extreme temperatures, they bury themselves in sand to protect themselves from the sun. They then use channels on their skin, located between their scales, to draw moisture from damp sand and transport it to their mouths like a straw.

They can also change color to help them regulate their body temperature and metabolism. In the cooler mornings, the lizards are a drab brown, becoming a lighter yellow as the temperature rises and they become more active. The lighter coloring likely helps reflect the sun and prevents them from overheating. However, they can also change color quickly in order to camouflage themselves.

Thorny devils are named after a human sacrifice god. Their scientific name, Moloch horridus, was inspired by John Milton's poem "Paradise Lost," which references the Canaanite god Moloch — a bloodthirsty figure that requires child sacrifices. The Latin word horridus means rough, dreadful, wild or frightful. According to research, a thorny devil was first exhibited in London by naturalist and businessman John Gould in 1840, but it was given its scientific name by zoologist John Gray in 1841, who allegedly had Milton’s epic poem in mind at the time.

In reality, though, thorny devils are harmless — unless you're a predator or an ant. They can consume thousands of the insects a day, using their sticky tongues and hard teeth to capture ants.

A Burmese python has been spotted attacking and swallowing a reticulated python. The unusual encounter could be the first known case of these species — two of the world's biggest snakes — preying on one another, scientists say.

Researchers in India observed the rare event in 2020, and images captured the moment the Burmese python (Python bivittatus) began feasting on the reticulated python (Malayopython reticulatus) from the tail up, while it was still alive. It took about two hours for the snake to be completely consumed, scientists reported in a research note published Aug. 20 in the journal Reptiles and Amphibians.

"It was a really unusual situation to find two pythons in the same area," study co-author Ashikur Rahman Shome, a wildlife ecologist at Dhaka University in Bangladesh, told Live Science.

When the scientists arrived, the 10-foot-long (3 meters) Burmese python was coiled around the slightly larger reticulated python's tail. The latter tried to fight back by constricting the Burmese python, but it eventually loosened its grip and was swallowed from the tail end up.

Related: The biggest snake in the world (and 10 other giant serpents)

Burmese pythons can grow to 19 feet (5.8 m), while reticulated pythons can reach up to 25 feet (7.6 m). In thi case, the reticulated python was larger than the Burmese, but the exact length was not taken, Shome said.

The event took place on the Akiz Wildlife Farm in Bangladesh's Chittagong Division. This area is one of the few places where the ranges of Burmese and reticulated pythons overlap. The two snake species prey on similar animals, such as mammals, birds and lizards.

It's not completely clear why the reticulated python was eaten, but given the better food options at the site, it might just have been a territorial dispute that ended up with one eating the other as an easy way to end the fight: "There are a number of chickens at the site. They make a better meal," Shome said.

"To the best of our knowledge, this observation represents the first documented predation of M. reticulatus by P. bivittatus," the team wrote in the paper.

Australia has a crocodile problem. In the last two decades, attacks have risen sharply after the population exploded. Along with safety messaging, government officials are increasing the number of permitted crocodile kills, but experts say the move isn't likely to work given how mobile crocodiles are — kill one, and another will immediately move into its territory.

But a new, stealthy way of preventing attacks may be on the horizon. The tool involves using the genetic fingerprints of crocodiles to identify areas where these predators are present. By harnessing environmental DNA (eDNA), wildlife officials could test waterways and warn swimmers, boaters and campers to avoid areas where crocodiles are, or have recently been.

The croc problem is partly the result of one of conservation's greatest success stories. In the early 20th century, thanks to overhunting, the Australian crocodile population plummeted to around 3,000. After protections were introduced in the 1970s, the population surged, and now an estimated 100,000 live in waterways across the country.

Because of this rise, both crocodile attacks and retaliatory attacks by humans are increasing. In the latest incident, on Aug. 3, 40-year-old David Hogbin fell into the Annan River in Queensland and was killed by a 16-foot-long (5 meters) saltwater crocodile (Crocodylus porosus), which was later killed by wildlife officials. And in 2023, a 13-foot (4 m) crocodile was found beheaded on a beach. A few months later, a 40-year-old female croc was also found dead, having been butchered with just her head and spine remaining.

Related: 'Eyes coming straight for me': Huge crocodile launches itself into boat with jaws wide open in strange attack

One reason it's hard for people to avoid croc attacks is that they are some of the world's ultimate ambush predators. They can sit completely still underwater for up to eight hours, waiting for unsuspecting prey to pass by before they strike. From the surface, the water may seem croc-free, but people should "assume crocodiles are present in all waterways," according to advice from the Northern Territory Government.

So researchers are developing tests that will show where crocodiles are — without ever needing to see them.

"Environmental DNA (eDNA) relies on detecting trace amounts of DNA that all living organisms leave behind … things like hair, skin cells, feces or urine," Elise Furlan, a molecular ecologist with the University of Canberra (UC) who works on the program, told Live Science in an email.

To test for eDNA, the team collects water samples and filters them. The scientists then extract any detectable DNA in the lab, amplifying it and searching for evidence of croc DNA, Furlan said.

To check the test's accuracy, the team searched for eDNA in water from crocodile-holding ponds at a Queensland Department of Environment, Science and Innovation (DESI) facility and compared the results with those from water that never housed crocodiles. After the crocodiles were removed from the pond, they tested the water to establish how quickly the DNA degrades, according to a statement from the DESI. This should reveal how long a crocodile needs to be in a body of water for it to be picked up by the tests, and how long after it has left the area its traces remain.

The program is in its early stages. Right now, samples need to be analyzed in the lab, but the researchers hope that as the work progresses, they can develop a spot-test to detect crocodiles in real time, Furlan said. The tests are not 100% accurate and there's a risk of false negative detection, but it's still likely to be better than traditional detection methods, Furlan said..

The hope is eDNA tests could be used in conjunction with other attack-prevention tools, such as public safety messaging.

In future work, the team plans to sample rivers and other water bodies in Queensland where crocodiles are present to establish the tests are effective in real-world environments.

"This research absolutely has the potential to have a very practical application," Furlan said.

"When the cobra runs for her life, she goes like a whiplash flicked across a horse's neck," Rudyard Kipling wrote of the villainous cobra Nagaina in his story of the heroic mongoose Rikki-Tiki-Tavi. And this whiplash motion may have helped real-life cobras and their relatives spread from Asia, where they originated, to the rest of the world.

Scientists once believed that Elapoidea, the superfamily containing cobras, coral snakes and mambas, originated in Africa. A fossil of a file snake found in Tanzania and dated to the Oligocene Epoch (33.9 million to 23 million years ago) supported this hypothesis — it is the oldest relative of this group discovered in the fossil record.

But in new research, published Aug. 7 in the journal Royal Society Open Science, researchers used genetic analysis and fossils from other regions to conclude that these snakes, as well as snakes in the related superfamily Colubroidea, actually originated in Asia.

"The reason for the uncertainty was mostly because of the lack of understanding of how these different species are related to one another," lead author Jeffrey Weinell, an evolutionary biologist and postdoctoral fellow at the American Museum of Natural History, who conducted the research while at the University of Kansas, told Live Science.

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Scientists had never compiled comprehensive genetic data on the group before, he explained. "I was interested in inferring the tree of life for this group, which predicts the evolutionary relationships, and then using that tree of life estimate plus information about modern species to estimate where the ancestor of this group lived," he added.

In the new study, Weinell and colleagues analyzed 3,128 locations on the genomes of 65 species of Elapoidea to decipher how all the snakes were related. They also included additional data from 434 other species, some of which had already been compiled in genetic databases and some of which they sampled themselves. These species were then mapped to depict their historical geographic distribution.

They found that the earliest ancestors of Elapoidea evolved in Asia between 28.94 and 45.92 million years ago and that Colubroidea emerged some 31.13 to 48.81 million years ago.

These early Asian ancestors may not exist in the fossil record due to the conditions where they evolved. "Tropical Asia is not the best for preserving fossils because of the climate," Weinell said.

These snakes left Asia for Africa, between 37.5 million, at the earliest, and 24.4 years ago and their descendants then dispersed into Europe, Australasia and the Americas in multiple waves. There are now 700 species, on every continent except Antarctica and many islands as well. Even the seas have been colonized by these early snakes' descendants.

The study found these snakes had a convoluted evolutionary history. Elapoids and colubroids likely moved into Africa from Asia on at least 15 different occasions, for example. And they recolonized Asia from Africa at least seven times, indicating the complexity of their movement between landmasses and underscoring the difficulty of tracing their origins.

As to how they got from one continent to the other, Weinell suspects that these snakes may have taken a variety of paths — using land bridges and even crossing narrow marine passages, to achieve their global distribution today.

In this adapted extract from "Bite: An Incisive History of Teeth, from Hagfish to Humans" (Algonquin Books, 2024), author and vertebrates zoologist Bill Schutt investigates the extraordinary bite force of living crocodilians, as well as their formidable predecessors, Deinosuchus and Sarcosuchus — the "most forceful biters in history."

"There are no 'pretty good' crocodilian researchers, Gregory Erickson quipped. “In my business, if you're not very good, you're missing an arm or something." Erickson, a professor of anatomy and vertebrate paleobiology at Florida State University, also emphasized that it takes a team of experienced handlers to secure the larger specimens. "We always have four or five people who really know their stuff."

Though Erickson has a range of research interests, I’d contacted him because of his research into the biting behavior of alligators, crocodiles and their relatives,

Once strapped down, a tap on the snout usually causes the test subject to open its mouth, after which the bite bar is placed onto the rear teeth. That's because the laws of physics dictate that a measurement taken closest to the jaw joint will provide the greatest bite force.

This placement also stimulates something akin to the knee-jerk reaction you might have experienced while being examined by a rubber-mallet-wielding physician. Here, though, the reflexive response by the crocodilian is to chomp down on the bite bar with full force. Although Erickson's first experiments centered on alligators (which makes perfect sense, given his Florida location), eventually he and his coworkers were able to obtain bite-force data on all 23 species of extant crocodilians, a group that includes crocodiles, alligators, caimans (alligator relatives from Central and South America), and gharials (narrow-snouted piscivores).

"We try to do three to five [individuals] of each species," Erickson said, emphasizing that this practice increased the chances of obtaining a true indication of the bite forces for that species. Ultimately, the largest animals they measured were several 17-foot (5.2 meters) saltwater crocodiles (Crocodylus porosus), which, along with the Nile crocodile (Crocodylus niloticus), happen to be the species involved in the greatest number of fatal and nonfatal attacks on humans.

Erickson and his fellow researchers were interested in determining how bite forces varied between species. Before their study, there had been several hypotheses predicting that bite forces in crocodilians would vary depending on factors like tooth shape, or the length or width of the jaw — variables that were readily observable traits commonly used to identify the species in question.

In something of a surprise, though, Erickson and his colleagues found that bite force was solely dependent on body size. "We got the same regression lines pound for pound," he told me. In other words, if you had a crocodile, alligator and caiman, each weighing 100 pounds (45 kilograms), their bite forces would be the same.

All the smaller species had smaller bite forces. The 17-foot saltwater crocodiles generated a bite force of 3,700 pounds (1,680 kg), but when those numbers were scaled up to the historically recorded 23-footers (7 m), Erickson said, "7,700 pounds [3,500 kg] is not infeasible."

There were, however, two exceptions to the size/bite force correlation: the two species of gharials (Gavialis gangeticus and Tomistoma schlegelii), whose long, skinny snouts look oddly out of place attached to a body that can reach 12 to 15 feet (3.7 to 4.7 m) in length or more and weigh in at up to 2,000 pounds (900 kg).

Their extremely elongated jaws are equipped with 110 interlocking, needle-like teeth, and the whole setup is wonderfully well adapted for slashing through the water with little resistance. But their bite force is significantly below expected values for critters of that size. Erickson believes the gharials' specialized fishing tackle is the cause, and that it resulted in an evolutionary trade-off in which greater bite force was sacrificed for the sake of rapid fish-snatching ability, made possible by an extremely long set of toothy jaws.

Unfortunately, the two living species of gharials are critically endangered. Within the gharials' riverine habitats on the northern Indian subcontinent, their numbers may have fallen to levels measured in the hundreds of individuals. Except for the narrow-nozzled gharials, all crocodilians, no matter their size, come equipped with some seriously powerful jaws.

Erickson hypothesizes that this adaptation evolved in ancestral crocodilians during the age of dinosaurs, enabling them to carve out an ecological niche along the water's edge that they've successfully held for over 100 million years. He compared crocodilian diversity to starting out with a big, powerful engine, then tweaking the attachments you could add to that megaforce-generating machine — tweaks that would include variation in the length, width and shape of the "stuff out in front of the eyes" (Erickson's term for the jaws and teeth). These attachments helped the different crocodilians become better adapted to prey on a variety of creatures, from mollusks to fish, and from birds to big game.

When considering the bite of a crocodilian, Erickson stressed the fact that just as important as the total force a crocodilian jaw might produce is the surface area where that force is being applied — in other words, the force per unit area, or pressure. That's because this measurement not only factors in the forces generated but also the shape of the tooth.

Erickson compared a pointy tooth like a crocodile canine to a shoe with a stiletto heel, which he described as more capable of damaging a wooden floor than a shoe with a flat sole. The force applied to the ground by the high-heel wearer is distributed across a smaller unit of area (the tip of the high heel) than it would be across the broad, flat sole of a sneaker. In pointy canine teeth, the bite force is distributed over a small surface area at the tooth tip, making them effective for piercing a prey's skin or hide.

Conversely, flat teeth, like premolars and molars, distribute bite forces over a greater surface area, making them ideal for turning large chunks of food into smaller chunks.

Of course, I was interested in the greatest bite force ever generated by an animal, extinct or extant, so I asked Erickson. He told me that was a tough question (presumably in part due to the scarcity of researchers during the age of dinosaurs) but that data points to a pair of prehistoric apex predators.

The first is Deinosuchus, a now-extinct crocodilian relative of modern alligators. Deinosuchus lived around 82 million to 75 million years ago in what is now the United States, where it reached lengths of almost 33 feet (10 m). "I don't think that any animal that has ever lived could have broken the grip of Deinosuchus," Erickson told me.

"So, what about escaping the grasp of an adult American alligator (Alligator mississippiensis) nowadays?" I wondered. "How hard would that be?"

"The bite force of a very large alligator is about 3,000 pounds [1,360 kg], about the weight of a small car," Erickson said. "So if you can bench press a car, you are good to go … If not, you're lunch."

The second contestant in the Greatest Bite Force of All Time Contest is Sarcosuchus. With a body length of about 40 feet (12 m), this behemoth lived in what is now South America and Africa 133 million to 112 million years ago. Sarcosuchus is classified as a crocodyliform (a "crocodile-like" creature). This means that although it certainly had the look of a card-carrying crocodilian, Sarcosuchus is not believed to be an ancestor of modern crocodiles and their relatives.

Still, Erickson believes that, like Deinosuchus, Sarcosuchus was generating a bite force of 20,000 pounds (9,000 kg), a number that his team estimated by scaling up the data from extant crocodilians. "I think they were right up there with the most forceful biters in history," he told me.

There are apparently limits, though, on the amount of bite force that can be generated. These relate to how much stress can be placed on the enamel covering of a tooth before it shatters. But, Erickson reminded me, this type of creature has a safeguard against that potential disaster. "Crocodilians all break their teeth," he said. "But they have one advantage over mammals — they can replace their teeth throughout their lives."

From "Bite: An Incisive History of Teeth, from Hagfish to Humans" by Bill Schutt. Used with permission of the publisher, Algonquin Books. Copyright © 2024 by Bill Schutt. This excerpt has been edited for space and clarity.

A captive snake in Australia has broken the world record for the most venom produced in one go, according to the creature's keepers.

With a single bite, the snake — a coastal taipan (Oxyuranus scutellatus) named Cyclone — ejected more than 0.18 ounces (5.2 grams) of venom. That's three times the average amount produced by a coastal taipan and enough to kill 400 humans, according to the Australian Reptile Park, a zoo located 30 miles (50 kilometers) north of Sydney in New South Wales.

"Cyclone is one of our most dangerous snakes here at the park and is known for being quite unpredictable and keeping us all on our toes," Billy Collett, the operations manager at the Australian Reptile Park, said in a statement shared with Live Science.

Coastal taipans are one of the most venomous snake species on Earth. They are native to coastal regions in northern and eastern Australia and typically grow to 6.6 feet (2 meters) long, according to the Australian Museum. Coastal taipans have a rectangular head with a pale snout and large, orange-brown eyes. Their bodies vary in color from yellow to reddish-brown, dark brown and almost black.

Related: Why does Australia have so many venomous animals?

"Coastal taipans are not the most venomous snake in the world, but they are known worldwide for their aggression and bites have caused fatalities every year," Collett said.

The previous venom yield record belonged to another coastal taipan at the park called Whiplash, which produced 0.17 ounces (4.9 g) of venom from a single delivery in 2022.

The park is the only facility in Australia that "milks" taipans to produce antivenom, Collett said. Keepers also extract venom from other deadly snakes, including eastern brown snakes (Pseudonaja textilis), tiger snakes (Notechis scutatus), death adders (Acanthophis) and black snakes (Pseudechis).

Milking snakes can be dangerous, according to the statement. "The process of milking a venomous snake requires keepers to secure the … snake, sink its fangs into a large shot glass covered with plastic and get it to deliver its lethal bite," Collett said. The venom is then freeze-dried, meaning it is dehydrated at low temperature, and sent to a vaccine manufacturer, Collett said.

Cyclone's record-breaking venom contribution will go toward saving someone's life, according to the statement. Around 3,000 snake bites are reported every year in Australia, resulting in approximately 500 hospital admissions and an average of 2 deaths. According to the Australian Snakebite Project, coastal taipans bit 31 people between 2005 and 2015, and although no deaths were found in that project, another study recorded at least one death between 2000 and 2016.

A captive snake thought to be male recently gave birth to 14 babies after almost a decade in isolation, its keepers say. 

The 13-year-old Brazilian rainbow boa (Epicrates cenchria), named Ronaldo, has not been in contact with any other snake for at least nine years. Ronaldo was a rescue snake that a vet had previously identified as a male. 

"One of the students discovered them during a routine vivarium check," Amanda McLeod, an animal care technician at the City of Portsmouth College in the U.K., where the snake is kept, said in a statement Monday (June 24). "At first we thought she must have been mistaken. We couldn't believe our eyes!"

This is the third  "virgin birth" recorded in a Brazilian rainbow boa. 

"Ronaldo had been looking slightly fatter than usual, like he'd eaten a big meal, but we never thought for a moment that he, or should we say she, was pregnant," Pete Quinlan, a reptile specialist at the college, said in the statement. 

Related: 8 animals that have virgin births

Virgin birth, known as parthenogenesis, is a type of asexual reproduction that takes place in a species that normally reproduces sexually. While rare, it's been recorded in several species in captivity, including birds, sharks, lizards, other snake species and a crocodile. 

In parthenogenesis, eggs mature without fertilization by sperm. In some cases, eggs can be fertilized by a "polar body," which is a small cell that forms in the reproductive tract at the same time as an egg cell. 

There are several different ways parthenogenesis can occur, and it is unclear what mechanism triggered Ronaldo to produce offspring. 

"Effectively the babies are clones of their mother although their markings are all slightly different," Quinlan said. 

Ronaldo was brought to City of Portsmouth College after being rehomed there by an animal welfare charity. The snakelets are now being assessed to determine their sex and placed in new enclosures. Once large enough, they will be rehomed, according to the statement. 

For more than 100 years, researchers assumed that dinosaurs were like giant lizards: sluggish reptiles that spent most of their day basking in the sun. This image changed when we started to realize that dinosaurs were far more similar to birds than to modern-day lizards. Today, researchers agree that birds are technically dinosaurs — the only ones to have survived the mass extinction 66 million years ago. Yet, if that's true, why aren't birds cold-blooded like most modern-day reptiles?

The answer is straightforward: Most dinosaurs were probably warm-blooded, too. 

Birds are descended from a diverse group of two-legged dinosaurs called theropods, which included giant, meat-eating predators like Tyrannosaurus rex, as well as the smaller 3-foot-long (1 meter) Mononykus. 

Like mammals, birds are warm-blooded, or endothermic, meaning they internally regulate their own body temperature. Endothermic animals have a higher metabolism, which permits more physically demanding activities — like flying — but requires more calories to maintain. 

"Animals that are warm-blooded are usually more active," Holly Woodward, a professor of anatomy and paleontology at Oklahoma State University, told Live Science. "They can be active into the night. And so it's an evolutionary strategy in that you can be foraging for food when other animals can't, because they're too cold and slow." 

Related: What happened when the dinosaur-killing asteroid slammed into Earth?

Birds generally have a higher metabolism than similarly sized mammals and keep their body temperatures up — between 106 and 109 degrees Fahrenheit (41 to 43 degrees Celsius). Hummingbirds, which flap their wings 720 to 5,400 times per minute, need to consume about half their body weight every day, or eat every 10 to 15 minutes. 

In contrast, cold-blooded animals, or ectotherms — like most modern reptiles and fish — rely on their environment to change their body temperature. Because they don't expend as much energy heating themselves, they don't need to eat as regularly; alligators, for example, can go more than a year without food. 

For years, researchers assumed that because most modern reptiles are ectothermic, ancient reptiles must have been, too. 

"So often, if you look at living animals and make an assumption about the ancestral state based on the current condition, it will lead you wrong," Jingmai O'Connor, associate curator of fossil reptiles at the Field Museum in Chicago, told Live Science. 

Views started changing around the late 1960s, with the discovery of a bird-like specimen called Deinonychus. Since then, researchers have found physical characteristics that indicate many dinosaurs, including ancient birds, were warm-blooded. The presence of feathers is one such indication — feathers help animals conserve body heat, which isn't needed in ectotherms. 

In her lab, Woodward has been looking at another proxy: bone tissue microstructure. She's found that endotherms have much different bones than ectotherms, mostly because ectotherms usually grow more slowly. This growth rate is reflected in the bones' mineral component, which she described as "little fibers."

"I imagine them kind of as Pick-up sticks: If you're growing really slowly, those fibers tend to orient themselves parallel to each other, and so they become flat," Woodward said. "But if you're growing faster, the fibers are just sort of a jumble," which is the type of structure she tends to see in warm-blooded bones. 

Her observations have shown that dinosaurs' bone structures are more similar to birds' and mammals' than to crocodiles'. 

Exactly when warm-bloodedness first popped up is unclear. All dinosaurs (including birds) and crocodiles share a common reptilian ancestor, and both Woodward and O'Connor said there's good evidence this ancestor was warm-blooded — meaning endothermy arose prior to dinosaurs. Cold-blooded dinosaurs would have appeared later. 

But it's possible endothermy showed up even earlier. If both mammals and most reptiles were endothermic, perhaps their common ancestor, which lived about 310 million years ago, was also endothermic. However, endothermy most likely evolved independently in mammals, O'Connor said. 

Future research could challenge these ideas, though. "We make so many assumptions," O'Connor said, "and then the data proves us wrong."

Earlier this year, the Western Pacific leatherback (Dermochelys coriacea) left a nesting site in the Solomon Islands and dove 4,409 feet (1,344 meters) beneath the ocean surface, according to the environmental organization The Nature Conservancy. 

At that depth, the leatherback swam deeper than the current Guinness World Record for the deepest turtle dive — 4,199 feet (1,280 m) — set by another leatherback, the deepest-diving reptile species. For context, Navy submarines have reportedly gone to depths of around 2,950 feet (900 m), while the deepest human scuba dive was 1,090 feet (332 m). 

Researchers recorded the dive as part of an ongoing and as-yet-unpublished satellite tracking study to help protect leatherbacks. Another of their tagged turtles swam across the entire Pacific Ocean. Peter Waldie, a marine scientist who leads The Nature Conservancy’s Solomon Islands Program, described the deep dive and epic migration as "truly spectacular."

"Leatherbacks are just an incredible creature to have in the world," Waldie told Live Science. "The ability to swim non-stop all the way across the Pacific, to dive as deep as a Navy submarine on a single breath, it absolutely blows my mind."

Related: What is the deepest-diving mammal?

Live Science approached Guinness World Records about the new claim for the deepest reptile dive. A spokesperson for the company said that the deepest dive by a turtle is one of their "consultant records," which they work with specialist experts to verify — usually after a scientific publication.

"For data-driven science and nature records such as this case, we would generally wait for the findings to be reviewed and published in a peer-reviewed journal before we consider it," the spokesperson said.

Leatherbacks have evolved a variety of adaptations for their deep dives. Even though they're air breathers like us, leatherbacks can hold their breath for much longer and stay underwater for around 90 minutes at a time. Their specialized carapace (upper shell) also contracts and expands with pressure changes to help them survive the deadly pressures of the deep.  

Scientists have a few theories as to why leatherbacks dive so deep, but tracking research has indicated they are swimming down to eat jellyfish, which move up and down the water column, Waldie said

Leatherbacks spend most of their lives out at sea, but females briefly come onto shore to lay their eggs. The Solomon Islands' nesting leatherbacks are part of the critically endangered Western Pacific population, comprising an estimated 1,400 breeding adults, according to the Nature Conservancy.  

"We have reached a point in conservation where we cannot afford to lose any of these creatures," Waldie said. "Every single breeding adult is vital, and every nest we can save that protects the next generation is vital."

Since 2022, Waldie and his colleagues have tagged 17 leatherbacks nesting in Isabel Province on the Solomon Islands, where The Nature Conservancy's local community rangers protect sea turtles and their eggs from poaching and predators. 

The record-breaking leatherback laid her eggs at the Sasakolo nesting beach. Staff named her "Uke Sasakolo," meaning "from Sasakolo." She broke the current depth record on March 25, not long after leaving the nesting grounds, according to Waldie.   

Uke Sasakolo nested during the peak Solomon Islands nesting season, which occurs between November and January. The tagged leatherbacks tended to then migrate south into southern Australian and New Zealand waters, according to Waldie. But one nester that arrived in June headed east. 

"Aunty June," as she was named, went straight across the Pacific and ended up in feeding grounds just off the coast of Baja California in Mexico. Waldie hopes further research will confirm whether mid-year nesters like Aunty June commonly take this eastern migration route, while peak season nesters like Uke Sasakolo head south.

"We call them all the Western Pacific nesters, but we might find that these nesting subpopulations are heading to completely different foraging areas," he said. 

Snakes escape predators by playing dead — and they make their performances even more convincing by smearing themselves with their own blood and feces, scientists have discovered.

Playing possum is common in the animal kingdom. Various insects, fish, amphibians, reptiles, birds and mammals all fake their own mortality in last-ditch efforts to fool predators. This behavior is known as death feigning or thanatosis. 

In a paper published May 8 in the journal Biology Letters, researchers described how dice snakes (Natrix tessellata) take their Shakespearean theatrics to the next level. 

When confronted by a predator, the snakes expel fecal matter and musk, a putrid digestive byproduct. They then flop on their backs and feign death, and sometimes they begin bleeding from the mouth, likely in an attempt to make themselves a less-appealing meal. 

"Death feigning is a high-risk, high-reward behavior. If you feign death, you're completely helpless, so it would be nice if you have some sort of protection against just being instantly consumed," lead author Vukašin Bjelica, a biologist at the University of Belgrade, told Live Science.

Dice snakes reach maximum lengths of about 4 feet (1.2 meters) and are nonvenomous, so they have few defenses against larger mammals and birds in their native range of Europe, Asia and northern Africa. 

But by deploying this suite of behaviors — known as a defense portfolio — dice snakes can make themselves seem unappetizing. The stench of the feces and musk and the bloody drool leaking from their mouths may give the impression that the snake is a rotting carcass rather than a fresh piece of meat. 

Related: Slow-motion footage of snake attacks reveals surprise discovery about how they kill

The revulsion and confusion that this macabre display evokes in a potential predator may provide just enough time for the snake to escape or even induce the predator to abandon its efforts entirely. 

The researchers focused on a population on Golem Grad, an island in Lake Prespa, North Macedonia. This population appears to be more predisposed to thanatosis than other populations of dice snakes. 

"The dice snakes from Golem Grad are in a peculiar set of circumstances. First of all, there is an intense avian predation pressure. Second, these snakes are rather large when compared to their mainland relatives," Bjelica said. "Being big is good if you're faced off against a gape-limited predator such as some birds."

They tested 263 dice snakes on the island by handling them in ways that simulated how a predator might approach its prey — grasping, holding and stretching its body. Of these snakes, 124 smeared feces on their bodies. Twenty-eight bled from the mouth — a phenomenon called autohemorrhaging or reflex bleeding. 

Bjelica thinks that individual personalities may determine whether the snakes engage in this behavior. "Some individuals are more bold — prone to risks — or shy — less likely to engage in risky behavior," he said.

Only one juvenile snake bled from the mouth, indicating that this behavior is more common in adults, and it may be too much of a risk for smaller snakes. "Juvenile snakes are smaller than adults and can easily be consumed. This might be one of the reasons they avoid this risky display," Bjelica said.

Dice snakes that expelled feces and musk and then bled from the mouth spent less time in a death-feigning state, the researchers found. The snakes that used fecal smearing and mouth bleeding spent an average of 2 seconds less in thanatosis, which the researchers believe to be significant survival advantage.

These snakes are not the only animals known to go the extra mile when playing dead. Virginia opossums (Didelphis virginiana) may defecate and drool while feigning death, indicating that this evolutionary strategy has proven useful across the spectrum of animal life.