It's hard to argue that the world is not made more interesting by singing whales the size of school buses, dinosaur-footed bird monsters that can leap clean over your head or slimy, cannibal salamanders that grow as large as crocodiles.
Giant animals like these are known as megafauna. Beyond being awesome in every sense of the word, these mammoth species are crucial to keeping their respective ecosystems balanced — and, according to a new study, about 60 percent of them are hopelessly doomed.
In new research published today (Feb. 6) in the journal Conservation Letters, scientists surveyed the populations of nearly 300 species of megafauna around the world, and saw some troubling trends emerge. According to the authors, at least 200 species (70 percent) of the world's largest animals are seeing their populations dwindle, and more than 150 face the risk of outright extinction.
The primary threat in most of these cases appears to be human meat consumption.
"Direct harvest for human consumption of meat or body parts is the biggest danger to nearly all of the large species with threat data available," lead study author William Ripple, a professor of ecology at the Oregon State University College of Forestry, said in a statement. "Our results suggest we're in the process of eating megafauna to extinction." [10 Extinct Giants That Once Roamed North America]
Earth's biggest beasties
"Megafauna" is a broad biological term that can apply to any number of large animals, equally apt for describing a chunky Australian codfish as a long-dead T. rex. To narrow down things in their new study, Ripple and his colleagues defined megafauna as any non-extinct vertebrate above a certain weight threshold. For mammals, ray-finned and cartilaginous fish (like sharks and whales), any species weighing more than 220 lbs. (100 kilograms) was considered megafauna. For amphibians, birds and reptiles, species weighing more than 88 lbs. (40 kg) made the cut.
This left the researchers with a list of 292 supersize animals. The list includes a cast of familiar faces like elephants, rhinos, giant tortoises and whales, as well as some surprise guests like the Chinese giant salamander — a critically endangered, alligator-size amphibian that can weight up to 150 lbs. (65.5 kg).
Next, using the IUCN Red List — an international database that assesses the extinction risks posed to more than 60,000 species — the researchers determined the level of threat faced by each of their 292 megafauna. They found that 70 percent of their megafauna sample showed decreasing populations, and 59 percent were threatened with total extinction.
According to the researchers, that makes megafauna far more vulnerable than all vertebrate species as a whole, of which 21 percent are threatened with extinction and 46 percent have declining populations. This bias against Earth's largest creatures is "highly unusual and unmatched" over the last 65 million years of post-dinosaur evolution, the authors wrote — and humans are likely to blame.
Human problem, human solution
As humans got better at killing from a distance over the past several hundred years, megafauna have started dying at an increasingly quick rate, the authors wrote. Since the 1760s, nine megafauna species have gone extinct in the wild, all thanks to human over-hunting and habitat encroachment.
Today, most of the threatened megafauna species face a lethal cocktail of human-induced dangers, including pollution, climate change and land development. However, the researchers wrote, the single biggest threat remains harvesting — that is, being hunted and killed for their meat or body parts.
"Meat consumption was the most common motive for harvesting megafauna for all classes except reptiles, where harvesting eggs was ranked on top," the researchers wrote in their study. "Other leading reasons for harvesting megafauna included medicinal use, unintended bycatch in fisheries and trapping, live trade and various other uses of body parts such as skins and fins."
This finding will come as sad but not-at-all-surprising news to anyone interested in animal conservation. It's hard to avoid headlines about sharks being hunted for their fins, African elephants slaughtered for their ivory or as trophies, or critically endangered rhinos — including the northern white rhino, of which only two individuals (both female) remain — killed for their horns.
According to the researchers, establishing legal barriers to limit the trade and collection of megafauna products is an essential step toward slowing this mass-extinction-in-progress.
Luckily, the world has seen some success with action like this before. In 1982, the International Whaling Commission adopted a moratorium on commercial whaling, which nearly 90 countries abide by today. Since then, "many of the largest marine mammals are in the process of recovering after the global cessation," the authors wrote. "This bold action required global cooperation and enforcement and has been successful in halting and reversing extinction threats for most of the great whales."
Originally published on Live Science.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Brandon is the space/physics editor at Live Science. His writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.