Archive image from page 110 of The dinosaur book the The dinosaur book : the ruling reptiles and their relatives dinosauruli13colb Year: 1945 turning and stopping. A stabilizer was pres- ent in the form of a large, fleshy dorsal fin, quite similar to the fin on the back of modern sharks and some porpoises. This fin kept the animal from rolling from side to side as it swam. So much for outward appearance. In the ichthyosaurs the skull was elongated, with the jaws pulled out to form a pointed beak or rostrum. These long jaws were armed with numerous sharp teeth—again patently a fish-catching
Archive image from page 110 of The dinosaur book the The dinosaur book : the ruling reptiles and their relatives dinosauruli13colb Year: 1945 turning and stopping. A stabilizer was pres- ent in the form of a large, fleshy dorsal fin, quite similar to the fin on the back of modern sharks and some porpoises. This fin kept the animal from rolling from side to side as it swam. So much for outward appearance. In the ichthyosaurs the skull was elongated, with the jaws pulled out to form a pointed beak or rostrum. These long jaws were armed with numerous sharp teeth—again patently a fish-catching device similar to that of the mesosaurs. It is an interesting fact that the teeth of the ichthyosaurs show a labyrin- thine internal structure, quite obviously an inheritance from their cotylosaurian and still more distant labyrinthodont pro- genitors. The eye was extraordinarily large. Evi- dently these animals depended for the most part upon vision to govern their movements. The eye opening of most fossil ichthyosaurs shows a ring of small overlapping bones known as sclerotic plates. The function of these plates is not clear, perhaps they helped to protect the large eyeball. As in all thoroughly streamlined swim- mers, the ichthyosaurs had no neck worthy of the name. The head was an integral part of the front of the body, a cutwater or prow that served as the 'entering wedge' for an animal moving through a dense medium. The advantage of an immobile, short neck in a fast-swimming animal is obvious. The body was flexible, for these animals must have propelled themselves in the same fashion as do fish, by a side-to-side flexion of the body, ending with a final push by the tail. Consequently the vertebrae, which in the land-living ancestors of the ichthyo- saurs were firmly held together by strong articulating processes, had in these aquatic reptiles become comparatively simple disks, similar in many respects to the vertebrae of fish. For in the ichthyosaurs there was no longer
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