Often compared to an Army tank or a bus, Ankylosaurus was a heavily armored dinosaur with a large club-like protrusion at the end of its tail. Ankylosaurus means "fused lizard" or "stiffened lizard" in Greek, and it was given that name because bones in its skull and other parts of its body were fused, making the dinosaur extremely rugged.
Ankylosaurus lived in the late Cretaceous Period, about 65 million to 75 million years ago and roamed the Western United States and Alberta, Canada. Due to its ability to secure an ample supply of food and ward off predators, paleontologists believe that Ankylosaurus was one of the last dinosaurs to face extinction.
While this herbivorous dinosaur was a massive animal, a re-examination of its fossils in 2004 downsized it a bit. Scientists believe it grew up to 35 feet (10.7 meters) long and six feet (1.8 meters) wide and about 4 feet (1.2 meters) tall. It weighed from 5 tons to 6.5 tons (4.5 kilograms to 5.9 kilograms).
The top of the dinosaur was almost completely covered with thick oval plates that were attached to its tough, leathery skin. This armor consisted of massive knobs and plates of bone, known as osteoderms or scutes, which are also common on crocodiles, armadillos and some lizards.
The plates, which varied in size, were aligned in regular horizontal rows down its neck, back and hips. There were also smaller plates or other similar features protecting the areas between the larger plates. Scientists believe that there may have also been smaller plates on its tail and limbs. [Related: Ancient Armored Fish Was Toothy, Too]
It had two rows of spikes along its body and large horns coming out of the back of its head as well as bony plates protecting its eyes. Its only vulnerable area was its belly. Infants and juveniles were thought to be more at risk from predators, which is why some paleontologists believe that Ankylosaurus traveled in packs to some degree to protect their young.
If the Ankylosaurus was attacked, paleontologists theorized that it would behave much like a porcupine and lie flat on the ground to protect its abdomen. Its weight, coupled with the row of short spikes running down its sides, made it hard to flip the animal over.
Scientists believe that the tail may have had flat triangular spikes that were arranged laterally along each side. The tail contained vertebrae that were woven together to form a stiff rod at the base of the club at the end. At one point paleontologists believed that the tail may have been used as a ruse to confuse predators into thinking it was the dinosaur's head, but that theory has since been discredited.
It is believed that the tail was used to swat at the occasional predator who tried to strike its unprotected underside and perhaps attract a mate. A 2009 study concluded that that the huge tail could easily have broken the bones of most of its predators
Ankylosaurus moved on all four limbs, although its hind limbs were slightly longer than its forelimbs. It was a very squat animal, only standing about 3 feet to 6.5 feet (1 meter to 2 meters) off the ground. Its top speed was only about 6 mph (9 kph) because of its heavy, low-slung body.
Although there are insufficient foot fossils to establish whether Ankylosaurus had toes, other it is likely that it had five toes on each foot as did other close relatives.
The dinosaur's triangular skull was wider than it was long and had a narrow beak at the end to aid in stripping leaves from plants.
What did Ankylosaurus eat?
Ankylosaurus grazed on low-lying plants. Its small leaf-shaped teeth were not designed to break up large plants and it had no grinding teeth. The dinosaur is believed to have had some sort of fermentation chamber or other internal mechanism for breaking down the massive amounts of unchewed food it ate.
The dinosaur is believed to have had a highly developed sense of smell, helping it to seek out food as well as avoid predators and competitors for its food supply.
A team led by American paleontologist Barnum Brown discovered the first Ankylosaurus fossil in the Hell Creek Formation of Montana in 1906. The remains included the top of a skull, as well as vertebrae, ribs, part of a shoulder girdle and armor.
Brown unearthed other Ankylosaurus remains, including scattered pieces of fossilized armor that he initially attributed to another dinosaur he called Dynamosaurus but are now believed to be Ankylosaurus fossils. He unearthed his third specimen in Alberta in 1910 when on an expedition at the Scollard Formation. This discovery included a complete skull and the first known tail club as well as ribs, limb bones and armor. All three of Brown's finds are housed at New York's American Museum of Natural History.
No complete Ankylosaurus skeleton has been unearthed to date. The largest known Ankylosaurus skull was discovered in 1947 in Alberta by Charles M. Sternberg.
Ankylosaurus track ways were found in 1996 in South American, near Sucre, Bolivia.
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