[Illustration: FIG. 57.—Front paddle of _Merriamia_, a Triassic ichthyosaur. (After Merriam.) Explanations as in Fig. 56.] And there was an increase in the ichthyosaurs, in some not only of the number of digits in each limb, but in all of the number of bones in each digit, a character found also in the unrelated mosasaurs and plesiosaurs. This increase in finger and toe bones, or hyperphalangy as it is called, is one of the most peculiar of all the adaptations to water life, changing the feet and hands from the ordinary walking type to the fish-like swimming type. The bones beyond the humerus and femur in the ichthyosaurs were so increased in number and so changed in form and relations that they bear little resemblance to the corresponding bones of other reptiles. They are merely polygonal platelets of bone, articulating on all sides and fitting closely together, permitting flexibility, but not much else. It is now believed that the increase, not only of additional digits, sometimes to as many as ten in each hand and foot, but of the finger and toe bones as well, was the result of a sort of vegetative reproduction. The margins and ends of the flippers were doubtless hardened by cartilage or fibrous material, and because of the action of the limbs this cartilagenous material broke up into nodules each of which took on ossification finally. Among the whales, where hyperphalangy also occurs, though to a less extent, it has been thought that the increase in number has been due simply to the ossification of the parts of each bone normally present, that is, to the epiphyses, which became separated from the shaft of each bone. But this explanation will hardly suffice for the fingers and toes of the plesiosaurs and ichthyosaurs, for there are altogether too many such ossifications; and besides, the bones in these animals, as in most reptiles, did not have epiphyses, or terminal separate ossifications of the bones of the skeleton. It will be observed from the figures that the arm and thigh bones of _Ichthyosaurus_ are very much shortened—a striking adaptation to water life, so conspicuously seen in the modern whales and dolphins as well as in the mosasaurs, thalattosaurs, etc. So characteristic indeed is this shortening that, were every other bone of the skeleton of an ichthyosaur unknown save the humerus or femur, it would be quite certain from these alone that the animal was thoroughly aquatic in habit.