Fig. 247.—A, Molar tooth of Elephas planifrons, one-third of the natural size, showing the grinding surface—from the Upper Miocene of India; B, Profile view of the last upper molar of Mastodon Sivalensis, one-third of the natural size—from the Upper Miocene of India. (After Falconer.) plates of enamel united together by ivory; and by the process of mastication, the teeth become worn down to a flat surface, crossed by the enamel-ridges in varying patterns; These patterns are different in the different species of Elephants, though constant for each; and they constitute one of the most readily available means of separating the fossil forms from one another. Of the seven Miocene Elephants of India, as judged by the characters of the molar, teeth, two are allied to the existing Indian Elephant, one is related to the living African Elephant, and the remaining four are in some respects intermediate between the true Elephants and the Mastodons.
The Mastodons, lastly, though quite elephantine in their general characters, possess molar teeth which have their crowns furnished with conical eminences or tubercles placed in pairs (fig. 247, B), instead of having the approximately flat surface characteristic of the grinders of the Elephants. As in the latter, there are two upper incisor teeth, which grow permanently during the life of the animal, and which constitute great tusks; but the Mastodons, in addition, often possess two lower incisors, which in some cases likewise grow into small tusks. Three species of Mastodon are known to occur in the Upper Miocene of the Siwâlik Hills of India; and the Miocene deposits of the European area have yielded the remains of four species, of which the best known are the M. Longirostris and the M. Angustidens.
Whilst herbivorous Quadrupeds, as we have seen, were extremely abundant during Miocene times, and often attained gigantic dimensions, Beasts of Prey (Carnivora) were by no means wanting, most of the principal existing families of the order being represented in deposits of this age. Thus, we find aquatic Carnivores belonging to both the living groups of the Seals and Walruses; true Bears are wanting, but their place is filled by the closely-allied genus Amphicyon, of which various species are known; Weasels and Otters were not unknown, and the Hyœnictis and Iditherium of the Upper Miocene of Greece are apparently intermediate between the Civet-cats and the Hyænas; whilst the great Cats of subsequent periods are more than adequately represented by the huge "Sabre-toothed Tiger" (Machairodus), with its immense trenchant and serrated canine teeth.
Amongst the Rodent Mammals, the Miocene rocks have yielded remains of Rabbits, Porcupines (such as the Hystrix primigenius of Greece), Beavers, Mice, Jerboas, Squirrels, and Marmots. All the principal living groups of this order were therefore differentiated in Middle Tertiary times.
The Cheiroptera are represented by small insect-eating Bats; and the order of the Insectivorous Mammals is represented by Moles, Shrew-mice, and Hedgehogs.
Lastly, the Monkeys (Quadrumana) appear to have existed during the Miocene period under a variety of forms, remains of these animals having been found both in Europe and in India; but no member of this order has as yet been detected in the Miocene Tertiary of the North American continent. Amongst the Old World Monkeys of the Miocene, the two most interesting are the Pliopithecus and Dryopithecus of France. The former of these (fig. 248) is supposed to have been most nearly related to the living Semnopitheci of Southern Asia, in which case it must have possessed a long tail. The Mesopithecus of the Upper Miocene of Greece is also one of the lower Monkeys,
Fig. 248.—Lower jaw of Pliopithcus antiquus. Upper Miocene, France. as it is most closely allied to the existing Macaques. On the other hand, the Dryopithecus of the French Upper Miocene is referable to the group of the "Anthropoid Apes," and is most nearly related to the Gibbons of the present day, in which the tail is rudimentary and there are no cheek-pouches. Dryopithecus was, also, of large size, equalling Man in stature, and apparently living amongst the trees and feeding upon fruits.