Ankylosaurus

ANKYLOSAURUS (an-KEE-loh-SORE-us)

Period: Late Cretaceous

Order, Suborder, Family: Ornithischia, Thyreophora, Ankylosauridae

Location: North America

Length: 23 feet (7 meters)

Next to Tyrannosaurus and Triceratops, Ankylosaurus is one of the best-known dinosaurs. Therefore, it may come as a surprise that this dinosaur is known only from three partial skeletons, none of which has been fully described. Its popularity mostly comes from a fanciful life-size restoration made for the 1964 New York World's Fair.

Through the studies of Walter Coombs, we now know that Ankylosaurus and all members of the family Ankylosauridae did not have spines and spikes projecting from the body as shown in the World's Fair restoration. Such spines and spikes only occur in the other ankylosaur family, Nodosauridae (see Sauropelta). Furthermore, there is no basis for showing keeled (ridged) rectangular plates in even rows across the body. Keeled plates have been found with the Ankylosaurus specimens, but these are different sizes and shapes. We don't know the arrangement of the plates on the body because no specimen has been found with the plates preserved as they were in life. The arrangement of plates is known for the nodosaurids Sauropelta and Edmontonia and the ankylosaurid Saichania. These specimens are important because they provide the only proof of how the armor looked in various species of ankylosaurs. The shape and arrangement of the armor is different on all three animals.

Like most armored dinosaurs, Ankylosaurus had bone plates fused (joined) to the outside of the skull and jaws. But unlike Sauropelta where there were many large plates, Ankylosaurus had many small plates. Ankylosaurus also differs from Sauropelta in having horns in the upper and lower corners of the skull behind the eyes. Why Ankylosaurus, and all ankylosaurids, developed these horns is not understood. They may have used them to fight among themselves. The animals would have stood side-by-side and swung their heads into the other's body. Such a blow would be painful but not fatal.

Ankylosaurus had a large bone club on the end of its tail. All members of its family had these clubs, and the lack of a club characterizes the other ankylosaur family, the Nodosauridae. The shape of the club is different for each member of the family. The club of Ankylosaurus was wide and long, but not very tall. The club in all the ankylosaurids was made of large armor plates fused together at the end of the tail. The bones of the tail were modified for swinging the club; they interlocked to form a "handle" to the club. This allowed Ankylosaurus to put force into the swing.