An Ankylosaurus lumbers along the shore of what’s now eastern Montana. Walking low to the ground, the dino uses its flat, leaf-shaped teeth to tear at ferns lining the water. Suddenly, a shadow looms over the herbivore—a Tyrannosaurus rex is hungry. But Ankylosaurus won’t be an easy meal.
Ankylosaurus was as large as a military tank and nearly as hard to attack, even though it was slow. Weighing about 10,000 pounds and measuring 30 feet long, scientists believe that the dinosaur couldn’t move any faster than a human can walk: about three miles an hour.
Its name comes from the Greek words for “fused lizard,” referring to its tough outer armor. Ankylosaurus had plates of bone connected under a layer of keratin—a protective protein found in hair and fingernails. These special bones even existed in its eyelids!
Ankylosaurus also had a club-shaped tail. If a predator attacked, the low and heavy reptile would swing its tail—made up of seven bones fused together in a hard and heavy mass—with enough force that it could break the bones of an ancient crocodile relative, which existed alongside Ankylosaurus.
Although its armor was impressive, Ankylosaurus wasn’t the only dinosaur to wear it. This reptile was part of a group of armored dinosaurs called thyreophorans, meaning “shield bearer.” Stegosaurus was also part of this group.
Fossils of Ankylosaurus have been found on every continent except Africa. These slowpokes lived 70 million to 66 million years ago but went extinct along with all the other non-avian (or non-bird) dinosaurs when a giant asteroid hit Earth.