No genus of quadrupeds has been more extensively diffused over the globe than the Mastodon. From the tropics it has extended both north and south into temperate regions, and in America its remains have been discovered as high as latitude 66° N. But the true home of the Mastodon giganteus, in the United States, like that of M. augustidens in Europe, lies in a more temperate zone, and, as Professor Owen says, we have no evidence that any species was specially adapted, like the Mammoth, for braving the rigours of an arctic winter. Now, we know from trustworthy geological evidence that the Mastodon is a much older form of life than the Mammoth. The record of the rocks tells us that it first put in an appearance in an early Tertiary period known as the Miocene (see Table of Strata, Appendix I.), and in the Old World lived on to the end of the succeeding Pliocene period. But in America several species, especially M. giganteus, survived till late in the Pleistocene period, where it was probably seen by primitive men. This is all that is known about its geographical range, and its antiquity or range in time; some day, perhaps before very long, palæontologists may be able to trace the great proboscideans further back in time, and to show from what form of animal they were derived. Strange as it may seem, anatomists declare that they show some remote affinity with the rodents, or gnawing animals, and, in some respects, even with Sirenians, such as the Manatee (see Chapter XVI.). But at present the evolution of this remarkable group of animals is an unsolved problem. Those strange animals, the Dinocerata, from Wyoming, described in Chapter X., may perhaps give some indication as to the direction in which we must look for the elephant's ancestors. We noticed that their limbs were decidedly elephantine (see p. 150), but they had no trunks, and their skulls showed curious prominences like horn-cores; their teeth too are very different. The visitor to the Geological Collection at South Kensington will also notice a splendid cranium of an elephant, with very long tusks, from the famous Sivalik Hills of Northern India[72] (Stand D on plan). It belonged to Elephas ganesa, one of the largest of all the fossil elephants known. The total length of the cranium and tusks is fourteen feet, and the tusks alone measure ten feet six inches in length! This remarkable specimen was presented by Sir William Erskine Baker, K.C.B. [72] There is some difficulty in determining the precise geological age of the strata in question, on account of the curious mixture of fossil forms of life they contain; but many authorities consider them to be of older Pliocene age.