. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. to the lightness of the skull, for in the thecodonts and their descendants the skull was in general light, vet strong and well braced. In addition, the pineal opening or "eye," so characteristic of the early reptiles, had disappeared. Finally, so far as skull char- acters are concerned, the thecodonts were typified by the limitation of the teeth to the edges of the upper and lower jaws; in other words, there were no teeth on the palate, as was so often the case among the more primitive Paleozo
. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. to the lightness of the skull, for in the thecodonts and their descendants the skull was in general light, vet strong and well braced. In addition, the pineal opening or "eye," so characteristic of the early reptiles, had disappeared. Finally, so far as skull char- acters are concerned, the thecodonts were typified by the limitation of the teeth to the edges of the upper and lower jaws; in other words, there were no teeth on the palate, as was so often the case among the more primitive Paleozoic reptiles. It was, however, in the pose and the manner of progression that the thecodonts developed their greatest difference from all other reptiles. We have seen in the fore- going pages how the first land-living verte- brates—the early tetrapods (TETT-ra-pods) evolved from certain fish, andTiow during the course of this evolution the four paired fins of the fish were transformed into four supporting limbs which enabled the animal to progress on land. Now in many of the reptiles the evolutionary specializations that have taken place have involved a strengthening or a modification of the four. The ancestors of the dinosaurs, the thecodonts, took to their hind legs and developed this special type of hip girdle limbs, and there has been a retention of the four-footed method of walking. In the thecodonts, on the contrary, there was an early adaptation for two-footed locomotion. These animals rose up on their hind limbs. There was a division of labor between the two sets of limbs; the hind legs became long and strong, for rapid running, while the fore limbs became very much reduced and handlike, to be used for grasping. Such a profound change in the posture of these reptiles naturally was reflected in their bodily structure. The body, instead of being supported fore and aft in the usual fashion, was "slung" at the hip joint, so that this joint became a sort of fulcru
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Keywords: ., bookauthoramericanmu, bookcentury1900, booksubjectreptilesfossil
