Ankylosaurus

What it was like

Ankylosaurus was a heavily armored plant eater built like a living tank. Bony plates called osteoderms covered its back and sides, and a mass of fused bone formed a club on the end of its tail. At about 8 meters long, it was among the largest ankylosaurs known, with a low, heavily built body to match. Its skull was wide and low, with small horns pointing back from the head. Rows of small, leaf-shaped teeth lined its jaws, suited to stripping tough plants rather than chewing them fine.

The tail club was probably a weapon. A swing from powerful hip and tail muscles could have delivered a heavy blow, useful against a hunting Tyrannosaurus or in disputes with other Ankylosaurus. Because its body was so wide and low, Ankylosaurus most likely moved at a slow, steady pace, relying on its armor rather than speed to stay safe.

Its world

Ankylosaurus lived at the very end of the Cretaceous period, from about 72 to 66 million years ago, just before the age of dinosaurs ended. Its fossils come from western North America, in places that are now Montana, Wyoming, Alberta, Saskatchewan, and South Dakota, preserved in rock layers such as the Hell Creek and Lance formations.

It shared its world with some of the best known dinosaurs of all: Tyrannosaurus, Triceratops, Edmontosaurus, and the small, quick Troodon. Plant-eating Thescelosaurus and the ostrich-like Ornithomimus and Pachycephalosaurus also roamed the same landscape of rivers and floodplains.

How it was found

Ankylosaurus was named in 1908 by Brown, based on fossils found in western North America. Paleontologists have since recorded 14 finds of the genus across five rock formations, yet no complete skeleton has ever been found. Scientists have had to piece Ankylosaurus together from partial remains, comparing them with better-known relatives such as Euoplocephalus and Saichania to fill in the gaps.