. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Kinds of Vertebrates aj The cotylosaurs, or stem-reptiles, were the earliest members of the group (Fig. 35a). Structurally they closely resembled the most primitive of the Amphibia. In external appearance they probably looked like the larger of our lizards. The therapsids, another early group, possessed certain features which indicate they were ancestral to the mammals (Fig. 35). Their teeth were differentiated into the three major types: cutting incisors;
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Kinds of Vertebrates aj The cotylosaurs, or stem-reptiles, were the earliest members of the group (Fig. 35a). Structurally they closely resembled the most primitive of the Amphibia. In external appearance they probably looked like the larger of our lizards. The therapsids, another early group, possessed certain features which indicate they were ancestral to the mammals (Fig. 35). Their teeth were differentiated into the three major types: cutting incisors; large, pointed canines; and grinding molariform teeth. Their jaws also showed a trend toward the mammalian plan. The dinosaurs (Fig. 36b, d, and h), including many species which varied widely in appearance, ranged in size from tiny forms about the size of a hen to the well-known enormous species which were the largest animals ever to walk on the face of the earth. Many of these reptiles were probably bipeds, capable of raising themselves up on their hind legs for more rapid running. To counterbalance the front parts of the body there was a long, rather heavy tail. The front legs, shorter than the hind legs, were presum- ably used when the animal was resting or walking slowly. These bipedal forms may have been close cousins of the earliest birds, both groups coming from the same immediate ancestral stock. The largest of the dinosaurs were undoubtedly quad- rupeds (four-footed). Apparently many of them developed amphibious habits, spending much of their time in lagoons and swamps where the water reduced the weight which it was necessary for their *ig" 37, _. A Pteros^ur- J (from JNewman, The legs to bear. Phylum Chordata, copy- Of the reptiles which returned to the water to right 1939, by permission live, the ichthyosaurs (ichthyo, fish; saur, lizard, of The Macmillan Com- ., N , . , . ... ,_. pany, publishers. After reptile) were the best adapted to aquatic life (Fig. Osbo
Size: 1776px × 1406px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
