It has been thought that these nothosaurs, so intermediate in structure between the true plesiosaurs and land reptiles, were the actual ancestors, but this is rather doubtful. It is probable that they were only very closely akin to the real ancestors, since in some ways they had become specialized too much, and, as we have already explained, highly specialized characters or organs can never go back to their earlier condition. The nothosaurs do prove beyond all possibility of doubt that the plesiosaurs were at least the descendants of animals closely allied to them, so closely, indeed, that it is doubtful whether we could distinguish external differences were all of them actually living at the present time. [Illustration: FIG. 49.—_Lariosaurus balsami_.] We have repeatedly seen that all aquatic animals have some or all the bones of the limbs shortened, and it is of interest to observe that the early plesiosaurs had longer forearm and foreleg bones than the later ones, just as we have seen was the case with the early ichthyosaurs. It would seem probable that all the early plesiosaurs had long necks, though some of the late ones in Cretaceous times had relatively short necks, shorter even than the known nothosaurs possessed. The nothosaurs doubtless lived about the shores of the ancient seas, spending much of their time in the water, leaving it perhaps when hard pressed by their enemies, as do some modern reptiles, or to rear their young. The teeth of the nothosaurs are long and slender in front, shorter behind. The animals must therefore have been carnivorous in habit, feeding probably upon such fishes as they could catch, and the various invertebrates which live in shallow water. The structure of the jaws and their attachments are quite as in the plesiosaurs, proving that they could not have swallowed large objects; but the skull is broader and flatter than that of most plesiosaurs, indicating habits not unlike those of the modern alligators and crocodiles. Some time we shall doubtless find remains of nothosaurs or nearly allied animals elsewhere than in Europe, but probably not from later deposits than the Triassic. So far as we now know, their geological range and geographical distribution were much restricted; they evidently wholly died out shortly after the plesiosaurs appeared. CHAPTER VII ANOMODONTIA LYSTROSAURUS