Description

Ankylosaurs weighed up to 4.5 metric tons (5 tons), and were about 10 meters (30 feet) long. While they were 1.8 meters (6 feet) wide, there were only 1.2 meters (4 feet) tall. Its legs were short, with the rear legs longer than the forelegs. It had five toes on each foot. The flat, triangular skull was thick, meaning the brain was quite small.

The flexible skin of an Ankylosaur was covered with thick, hard ovals of embedded bone, which superficially resembled the plates of an armadillo. The armor completely covered the entire surface of its head and exposed body; it even had bony shelves over its eyes.

Ankylosaurus also had short spikes lining both sides of its body. A set of horns stuck out from the back of its head, the two largest protruding from the corners. Unlike the Stegosaurus, the armor of the Ankylosaurus was attached directly to its skeleton, instead of being attached to its skin.

It also had a bony club on its tail which it could swing from side to side. The tail was muscular, so it probably made an excellent weapon when used for defense. The tail was made from hardened tissue, fused to the tail bones (caudal vertebrae).

Environment

Ankylosaurus existed between 65 and 70 million years ago, in the Maastrichian age of the Late Cretaceous period, and was one of the last dinosaurs before they were wiped out by the Cretaceous-Tertiary extinction event.

They were plant-eaters (herbivores). Being stiff and low-slung, they must have grazed on low-lying vegetation.

Even giant carnivores of the Maastrichian, like Tyrannosaurus, Deinonychus, and Tarbosaurus, probably could not break through ankylosaur armor. It is believed they would lie flat on the ground, hiding their soft stomach from attackers. Like a porcupine, they were only vulnerable when flipped over, which was made more difficult by the row of short spikes running down their sides.

Classification and history

The only species in the genera, Ankylosaurus magniventris, was named by Barnum Brown in 1908. Fossil remains have been found in Alberta, Canada, as well as in Wyoming and Montana in the United States. Euoplocephalus was originally believed to be an ankylosaur, but it now has its own genera.

The remains are fairly complete, including a couple skulls and the signature tail. A trackway of an ankylosaur was found in Sucre, Bolivia in 1996, which showed that the massive dinosaur could move fairly quickly.

Etymology

The name Ankylosaurus is derived from the Greek agkylos, meaning "bent" or "crooked", and sauros, meaning "lizard". This refers to the way the bony plates on its back have fused with the thick skin, and the way many of the internal supporting structures like the backbone (vertebrae) and ribs have also fused together.