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DINOSAURS

Chapter 8:

THE BEAKED DINOSAURS (Continued.)

C. The Armored Dinosaurs—Stegosaurus, Ankylosaurus.

Sub-Order Stegosauria.


This group of dinosaurs is most remarkable for the massive bony armor plates, crests or spines covering the body and tail. They were more or less completely quadrupedal instead of bipedal, with straight post-like limbs and short rounded hoofed feet adapted to support the weight of the massive body and heavy armature. Although so different superficially from the bird-footed biped Iguanodonts they are evidently related to them, for the teeth are similar, and the horny beak, the construction of the pelvis, the three-toed hind foot and four-toed front foot all betray relationship. From what we know of them it seems probable that they evolved from Iguanodont ancestors, developing the bony armor as a protection against the attacks of carnivorous dinosaurs, and modifying the proportions of limbs and feet to enable them to support its weight. They were evidently herbivorous and some of them of gigantic size. Smaller kinds with less massive armor have been found in Europe but the largest and most extraordinary members of this strange race are from North America.

STEGOSAURUS.

This extraordinary reptile equalled the Allosaurus in size, and bore along the crest of the back a double row of enormous bony plates projecting upward and somewhat outward alternately to one side and the other. The largest of these plates situated just back of the pelvis were over two feet high, two and a half long, thinning out from a base four inches thick. The tail was armed with four or more stout spines two feet long and five or six inches thick at the base. In the neck region and probably elsewhere the skin had numerous small bony nodules and some larger ones imbedded in its substance or protecting its surface. The head was absurdly small for so huge an animal, and the stiff thick tail projected backward but was not long enough to reach the ground. The hind limbs are very long and straight, the fore limbs relatively short, and the short high arched back and extremely deep and compressed body served to exaggerate the height and prominence of the great plates. The surface of these plates, covered with a network of blood-vessels, shows that they bore a covering of thick horny skin during life, which probably projected as a ridge beyond their edges and still further increased their size. The spines of the tail, also, were probably cased in horn.

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.

Fig. 35.: Skull and lower jaw of Armored Dinosaur Ankylosaurus, from

After Brown

Fig. 35.—Skull and lower jaw of Armored Dinosaur Ankylosaurus, from Upper Cretacic (Edmonton formation) of Alberta. Left side view.


ANKYLOSAURUS.

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.

Fig. 36.: Ankylosaurus, top view of skull in fig. 35.

After Brown

Fig. 36.—Ankylosaurus, top view of skull in fig. 35.

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.

Scelidosaurus, Polacanthus, etc. Various armored dinosaurs, of smaller size and less heavily plated, have been described from the Jurassic, Comanchic and Cretacic formations of Europe. The best known are Scelidosaurus of the Lower Jurassic of England, and Polacanthus of the Comanchic (Wealden). Stegopelta of the Cretaceous of Wyoming is more nearly related to Ankylosaurus.



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