These reptiles adapted themselves to the same type habitat that was occupied by the phytosaurs, which preceded them. Crocodiles and alligators were much larger and more abundant during Cretaceous and Cenozoic time than they are today; the crocodiles first appeared in the Cretaceous and the alligators in the Tertiary. The remains of both crocodiles and alligators have been found in Texas, and one such crocodile (_Phobosuchus_) represents the remains of the largest crocodile yet discovered (Pl. 43). This specimen probably had an overall length of 40 to 50 feet, and its massive skull was 6 feet long and possessed exceptionally strong jaws. The remains of this great beast were collected from exposures of Upper Cretaceous rocks along the Rio Grande in Trans-Pecos Texas. Pterosaurs.— These were Mesozoic reptiles with bat-like wings supported by arms and long thin “fingers” (Pl. 42). The pterosaurs were well adapted to life in the air, and their light-weight bodies and wide skin-covered wings enabled them to soar or glide for great distances. The earliest known pterosaurs were found in lower Triassic rocks, and the group became extinct by the end of the Cretaceous. During this time certain of these creatures attained a wingspread of as much as 27 feet, but their bodies were small and light. 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). [Illustration: 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.—