Dinosaurs.—
The collective term “dinosaurs” (meaning terrible lizards) has been given to that distinctive group of reptiles prominent in [Mesozoic] life for some 140 million years. In size, the dinosaurs ranged from as little as 1 foot to as much as 85 feet in length and from a few pounds to perhaps 45 tons in weight. Some were carnivorous (meat-eaters) but the majority were herbivorous (plant-eaters). Some were bipedal (walked on their hind-legs) while others were quadrupedal (walked on all fours), and although most of the dinosaurs were terrestrial in [habitat], aquatic and semi-aquatic forms were also present.
According to the structure of their hip bones, the dinosaurs have been divided into two great orders. These are the Saurischia (forms with lizard-like pelvic girdle) and the Ornithischia (dinosaurs with a bird-like pelvic girdle).
Plate 43
Dr. Brown, R. T. Bird, and Dr. Schaikjer with the skull of Phobosuchus, an extinct crocodile from the [Cretaceous] of Trans-Pecos Texas.
Photograph courtesy of the American Museum of Natural History.
Order Saurischia.—
Dinosaurs belonging to this order were particularly abundant during the [Jurassic] and are characterized by hip bones that are similar to those of modern lizards. These dinosaurs were first discovered in rocks of [Triassic] age and did not become extinct until the end of the [Cretaceous]. The lizard-hipped reptiles are divided into two rather specialized groups of dinosaurs: the theropods (carnivorous bipedal dinosaurs that varied greatly in size) and the sauropods (herbivorous, quadrupedal, semi-aquatic, usually gigantic dinosaurs).
SUBORDER THEROPODA.—
This type of saurischian dinosaur walked on bird-like hind limbs, and they were exclusively meat-eating forms, such as Allosaurus ([Pl. 44]) of [Jurassic] age. Some theropods were exceptionally large and were undoubtedly vicious beasts of prey. This assumption is borne out by such anatomical features as the small front limbs with long sharp claws for holding and tearing flesh, and the large strong jaws which were armed with numerous, sharp, dagger-like teeth. The largest of all known theropods was Tyrannosaurus rex which, when standing on his hind limbs, was almost 20 feet tall. Some individuals were as much as 50 feet long, and Tyrannosaurus is believed to have been among the most vicious animals to ever inhabit our earth. A [cast] of the skull of one of these great beasts is on display in the Texas Memorial Museum at Austin, and a Tyrannosaurus tooth has been found in the Big Bend National Park in Trans-Pecos Texas.