The last genus of the family Elephantidae is Mastodon, so called from the structure of the molar teeth. These are provided with but few transverse ridges, not more than five, so that their structure is intermediate between those of Dinotherium and those of Stegodon. Between the ridges are sometimes isolated, boss-like protuberances (whence the name of Mastodon), produced by a subdivision of the ridges. There is either but little or no cement between the ridges. This genus differs from nearly all other Elephantidae by the possession of milk molars, which occasionally persist throughout life, the permanent dentition in those cases being a mixture of milk and permanent teeth, as has been (erroneously) stated of the Hedgehog.[[138]]
The tusks (incisors) are sometimes present in both jaws, and as they have, during youth at any rate, a coating of enamel, the likeness to the chisel-shaped incisors of Rodents is patent. In connexion with the implantation of incisors in the lower jaw, many species have a prolongation of the bones of that part of the skeleton. In the bones, generally, there is not very much difference from Elephas, but the forehead is a little less pronounced. The genus existed from the Miocene and became extinct in the Pleistocene. It was nearly world-wide in range, being known from all four continents. Naturally with this very wide range was associated a large number of species. Zittel enumerates no less than thirty-two.
This genus is the only one of the Elephantidae which extended its range into South America, where the remains of two species occur. The bones of these great Elephants have attracted attention for some centuries. They were often held to be the bones of giants (as they actually were!), and in one case were ascribed to a deceased monarch, Teutobochus. The American Indians considered that equally gigantic men lived who were able to combat these great Proboscideans. There are legends of the Mastodons as living animals, which is quite probable, considering their geological age. There is a curious parallelism between the legends of two such widely-separated localities as North America and Greece. Buffon relates how among the Indians of Canada there was a belief that the Great Being destroyed both Mastodons and men of equal proportions, with thunderbolts. With this we may perhaps compare the story of the destruction of Typhoeus by Zeus, who
also used thunderbolts. One of the giants was not slain, but was compelled to stand and bear up the heavens. Atlas holds thus the position of the Elephant supporting the globe of Indian mythology.
Fig. 119.—Dinotherium giganteum. Side view of skull, 1⁄15th natural size. Miocene, Germany. (After Kaup.)
The genus Dinotherium, sole representative of the family Dinotheriidae, differs in a number of important particulars from the true Elephants. In the Elephants, if there is but a single pair of incisors, these are found in the upper jaw; in Dinotherium there is apparently but a single pair, but these are implanted in the lower jaw, the symphysis of which is much prolonged and greatly bent downwards, so that the tusks emerge at right angles to the long axis of the head, and are even bent backwards. The molar teeth are five in number on each side of each jaw and are bi- or tri-lophodont, not unlike those of the Tapir. There is no cement in the valleys between the ridges of these teeth, and there is a regular succession, the premolars being two and the molars three.[[139]] All the teeth are in use at the same time,
their small size enabling them to be accommodated in the jaw together. The skull of Dinotherium is lower than that of Elephas or Mastodon. The bones of the skeleton generally are like those of Elephas.
Though a suggestion of marsupial bones attached to the pelvis has been discredited, there is no doubt that Dinotherium occupies the most primitive position among the Proboscidea; but at the same time it cannot be regarded as the ancestor of Elephants, as it is so much specialised in various ways. The incisors for one thing forbid this way of looking at the creature. It is an ancient genus found in beds of Miocene age in Europe and Asia. It is not known from America. The creature was larger than any Elephant. Eighteen feet in length has been assigned to it. The enormous weight of the lower jaw and tusks seems to argue that it was at least partially aquatic in habit, and that it may have used these tusks for grubbing up aquatic roots or for mooring itself to the bank. At first there were naturalists who considered it as an ally of the Manatee, and the skull is not unsuggestive of that of the Sirenia.
Pyrotherium has been referred to the Proboscidea; but our knowledge of that form is limited to a few teeth from Patagonian rocks of an uncertain age.[[140]] They are simple bilophodont molars, very like those of Dinotherium. A tusk has been found in the neighbourhood of these teeth which may possibly belong to the same animal; but it is uncertain.