The sauropods were the largest of all dinosaurs, and some attained a length of 85 feet and probably weighed 40 to 50 tons (Brontosaurus, [Pl. 44]). They were primarily herbivorous dinosaurs which had become adapted to an aquatic or semi-aquatic type of existence and probably inhabited lakes, rivers, and swamps. The tracks of sauropod dinosaurs have been collected from Lower [Cretaceous] rocks in central Texas ([Pl. 4]) and Upper Cretaceous beds in Big Bend National Park in Trans-Pecos Texas.
Order Ornithischia.—
The ornithischian, or bird-hipped dinosaurs, were herbivorous reptiles which were quite varied in form and size and appear to have been more highly developed than the saurischians. This order includes the duck-billed dinosaurs (ornithopods), the plate-bearing dinosaurs (stegosaurs), the armored dinosaurs (ankylosaurs), and the horned dinosaurs (ceratopsians). Ornithischian tracks are known from [Cretaceous] rocks in central and Trans-Pecos Texas.
SUBORDER ORNITHOPODA.—
These unusual dinosaurs were predominantly bipedal, semi-aquatic, and some (like the duck-billed dinosaurs) were highly specialized (Trachodon, [Pl. 45]).
SUBORDER STEGOSAURIA.—
The stegosaurs were herbivorous, quadrupedal ornithischians with large projecting plates down the back and heavy spikes on their tails. The [Jurassic] dinosaur Stegosaurus ([Pl. 45]) is most typical of the plate-bearing forms. This creature weighed about 10 tons, was some 30 feet long, and stood about 10 feet tall at the hips. Stegosaurus is characterized by a double row of large, heavy, pointed plates which run along the animal’s back. These plates begin at the back of the skull and stop near the end of the tail. The tail was also equipped with four or more long curved spikes which were probably used as a means of defense. The animal had a very small skull which housed a brain that was about the size of a walnut, and it is assumed that these, and all other dinosaurs, were of very limited intelligence.
Stegosaurus remains have not been discovered in Texas, but these, like certain other of the extinct vertebrates, are mentioned because of their interesting and unusual form.
SUBORDER ANKYLOSAURIA.—
The ankylosaurs were four-footed, herbivorous, [Cretaceous] dinosaurs which had relatively flat bodies. The skull and back of the animal were protected by bony armor, and the club-like tail was armed with spikes. Paleoscincus ([Pl. 45]), a typical ankylosaur, had large spines projecting from along the sides of the body and tail. The armored spiked back and the heavy club-like tail probably provided Paleoscincus with much-needed protection from the vicious meat-eating dinosaurs of Cretaceous time.