Ankylosaurus was the Cretaceous equivalent of a Sherman tank: low-slung, slow-moving, and covered with thick, nearly impenetrable armor. Here are 10 facts you may or may not have known about Ankylosaurus.
1. Ankylosaurus was discovered early in the 20th century.
The "type fossil" of Ankylosaurus was discovered by the famous paleontologist (and P.T. Barnum namesake) Barnum Brown in 1906, in Montana's Hell Creek formation. Brown went on to unearth numerous other Ankylosaurus remains, including scattered pieces of fossilized armor that he initially attributed to a dinosaur he dubbed "Dynamosaurus" (a name that has unfortunately vanished from the paleontological archives!)
2. There are two ways to pronounce Ankylosaurus.
Technically, Ankylosaurus (Greek for "fused lizard" or "stiffened lizard") should be pronounced with the accent on the second syllable: ank-EYE-low-SORE-us. However, most people (including most paleontologists) find it easier on the palate to put the stress on the first syllable: ANK-ill-oh-SORE-us. Either way is fine--this dinosaur won't mind, as it has been extinct for 65 million years.
3. Ankylosaurus' armor was composed of osteoderms.
The most notable feature of Ankylosaurus was the tough, knobby armor covering its head, neck, back and tail. This armor was made up of "osteoderms," or "scutes," deeply embedded plates of bone (which weren't directly connected to the rest of Ankylosaurus' skeleton) covered by a thick layer of keratin, the same protein as is contained in human hair and rhinoceros horns.
4. Full-grown Ankylosaurus adults were immune from predation.
When full grown, Ankylosaurus weighed as much as five or six tons and was built close to the ground, with a low center of gravity. Even a hungry Tyrannosaurus Rex (which weighed twice as much) would have found it nearly impossible to tip over an adult Ankylosaurus and dig into its soft belly--which is why late Cretaceous theropods preferred to prey on babies and juveniles.
5. The brain of Ankylosaurus was unusually small.
As massive as it was, Ankylosaurus was powered by an unusually small brain--which was about the size as that of its close cousin Stegosaurus, considered to be the most dim-witted of all the dinosaurs. As a rule, slow, armored, plant-munching animals don't require much in the way of grey matter, especially when their defensive strategy consists of flopping down on the ground and lying motionless!
6. Ankylosaurus had a heavy, clubbed tail.
The armor of Ankylosaurus wasn't strictly defensive in nature; this dinosaur also wielded a heavy, round, dangerous-looking club on the end of its stiff tail. What's unclear is whether Ankylosaurus swung its tail to keep predators at bay, or if this was a sexually selected characteristic--that is, males with bigger clubs had the opportunity to mate with more females.
7. Ankylosaurus lived in a tropical climate.
During the late Cretaceous period, 65 million years ago, the western United States had a warm, humid, near-tropical climate. Considering its size and the environment it lived in, it's likely that Ankylosaurus possessed a cold-blooded (or at the very least homeothermic) metabolism, which would have allowed it soak up heat during the day and dissipate it slowly at night.
8. Ankylosaurus was a close relative of Euoplocephalus.
As armored dinosaurs go, Ankylosaurus is much less well-attested than Euoplocephalus, a slightly smaller (but more heavily armored) North American ankylosaur that's represented by numerous fossil remains, down to this dinosaur's eyelids. But because Ankylosaurus was discovered first--and because Euoplocephalus is a mouthful to pronounce--guess which dinosaur is more popular?
9. Dinosaurs like Ankylosaurus have been found all over the world.
Ankylosaurus has lent its name to a widespread family of plant-eating dinosaurs, the ankylosaurs, which have been discovered on every continent except Africa. The evolutionary relationships of all these armored dinosaurs is a matter of dispute, beyond the fact that ankylosaurs were closely related to stegosaurs; it's possible that at least some of their surface similarities can be chalked up to convergent evolution.
10. Ankylosaurus was one of the last dinosaurs to go extinct.
The near-impenetrable armor of Ankylosaurus, combined with its presumed cold-blooded metabolism, enabled it to weather the K/T Extinction Event better than most dinosaurs. Even still, Ankylosaurus populations slowly but surely died out 65 million years ago, doomed by the disappearance of the trees and ferns they were accustomed to munching on, as vast clouds of dust circled the earth in the wake of the Yucatan meteor impact.