ANKYLOSAURUS

armoured ornithischian dinosaur of North America during the Late Cretaceous Epoch (97.5 to 66.4 million years ago). Ankylosaurus gave its name to the ankylosaurs, an infraorder (Ankylosauria) of four-legged, herbivorous, heavily armoured dinosaurs that flourished throughout the Cretaceous Period. Ankylosaurus was the largest of the ankylosaurs, with a total length of about 10 m (33 feet) and a probable weight of about four tons. Its body was short and squat, with massive legs to support its weight. Like other ankylosaurs, its back and flanks were protected from attack by thick bands of armour consisting of flat bony plates. These plates were supplemented by rows of bony spikes projecting from the animal's flanks, and by bony knobs on its back. The skull was also heavily armoured and spiked. Ankylosaurus' long tail terminated in a thick knob of bone, which it probably swung like a club as a defense against predators. Other ankylosaurs varied the armour theme somewhat, but all were well-protected against attack by carnivorous dinosaurs.