Ankylosaurus was a short, squat, heavily armored dinosaur that was a member of the Ankylosauridae family. It was a little like a prehistoric porcupine — it had armor plates called osteoderms covering its back and sides, leaving its belly unprotected. Some of these plates had a ridge called a keel, although scientists aren’t sure exactly where on the body these scales appeared. Ankylosaurus also had short, dense legs to hold up its heavy body; it was 25 to 35 feet long and weighed three to four tons. Armor wasn’t Ankylosaurus’ only defense. It also had a club at the end of its tail. This club was formed by a set of tightly packed vertebrae covered in armor and could have been a powerful weapon.
Ankylosaurus’ tail wasn’t particularly flexible, though, so maneuvering it to strike a predator might have been difficult. Behind each of its eyes, Ankylosaurus had a pair of horns. These may have provided another line of defense against predators like Tyrannosaurus, or they may have been used for display or for fighting against rivals. Its mouth probably didn’t pose much of a threat, though. It was beaklike and had small teeth that were good for grabbing and chewing plants. Compared to the other members of the Ankylosauridae family, Ankylosaurus was relatively short-lived. It walked the earth for about 5 million years, while the family as a whole existed for close to 80 million years, throughout the entire Cretaceous period. Paleontologists have also found more fossils belonging to other Ankylosaurs than to Ankylosaurus. In fact, Ankylosaurus fossils are rare — researchers have only found two skulls and fewer than five incomplete skeletons. This means that much of what we know about Ankylosaurus comes from the study of its relatives. Ankylosaurus’ front legs were a little shorter than its back legs, and the shape of its vertebrae probably kept it from being able to lift its head. It probably ate low-lying vegetation, like grasses and shrubs.