This extraordinary animal was a contemporary of the Brontosaurus and Allosaurus, and its discovery was one of the great achievements of the late Professor Marsh. The skeletons which he described are mounted in the Yale and National Museums. Another skeleton was found in the famous Bone-Cabin Quarry, near Medicine Bow, Wyoming, by the American Museum Expedition of 1901. This skeleton, at present withdrawn from lack of space, will be mounted in the Jurassic Dinosaur Hall in the new wing now under construction.
[Illustration: Fig. 35.--Skull and lower jaw of Armored Dinosaur _Ankylosaurus_, from Upper Cretacic (Edmonton formation) of Alberta. Left side view. _After Brown_]
Related to _Stegosaurus_, equally huge, but very different in proportions and character of its armor was the Ankylosaurus of the late Cretacic. This animal, a contemporary of the Tyrannosaurus and duck-billed dinosaurs was more effectively though less grotesquely armored than its more ancient relative. The body is covered with massive bony plates set close together and lying flat over the surface from head to tip of tail. While the stegosaur's body was narrow and compressed, in this animal it is exceptionally broad and the wide spreading ribs are coössified with the vertebrae, making a very solid support for the transverse rows of armor plates. The head is broad triangular, flat topped and solidly armored, the plates consolidated with the surface of the skull and overhanging sides and front, the nostrils and eyes overhung by plates and bosses of bone; and the tail ended in a blunt heavy club of massive plates consolidated to each other and to the tip of the tail vertebrae. The legs were short, massive and straight, ending probably in elephant-like feet. The animal has well been called "the most ponderous animated citadel the world has ever seen" and we may suppose that when it tucked in its legs and settled down on the surface it would be proof even against the attacks of the terrible Tyrannosaur.
[Illustration: Fig. 36.--_Ankylosaurus_, top view of skull in fig. 35. _After Brown_]
This marvellous animal was made known to science by the discoveries of the Museum parties in Montana and Alberta under Barnum Brown. Fragmentary remains of smaller relatives had been discovered by earlier explorers but nothing that gave any adequate notion of its character or gigantic size. From a partial skeleton discovered in the Hell Creek beds of Montana, and others in the Edmonton and Belly River formations of the Red Deer River, Alberta, it has been possible to reconstruct the entire skeleton of the animal, save for the feet, and to locate and arrange most of the armor plates exactly. A skeleton mount from these specimens will shortly be constructed for the Cretaceous Dinosaur Hall.