In beds of the same age in South America is found a true Cheetah, a species now confined to the Old World. But the most wonderful animal belonging to this period is the great Sabre-toothed Tiger (_Machærodus_), a gigantic animal, with canines six or eight inches long, and jagged at their edges like a very fine saw. It would almost seem as if Dame Nature, in producing this terrible beast, had actually got to the end of her tether in the matter of specialisation for carnivorous habits; the canines of Machærodus were so long that he must have had some difficulty in opening his mouth sufficiently wide to take in anything large, and thus it would seem that he actually overshot the limit of perfection, and died of over-specialisation. The canines of the Sabre-toothed Tiger are, however, not its only peculiarity: there is one less premolar on each side of the upper jaw than in the modern members of the Cat family, so that the total number of teeth is reduced to twenty-eight,[196] the smallest number found in any of the Carnivora. On descending to the rocks of Pliocene age, we find, amongst many forms existing at the present day, an animal called _Galecynus_, about the size of the Fox, and possessing many characters, in its teeth, limbs, &c., intermediate between those of the Dogs and those of the Civets. Another genus, _Hyænarctos_, is almost exactly half-way between Dogs and Bears; its molars have less of a cutting character than a Dog’s, and less of a grinding character than a Bear’s, and its front premolars, though much smaller than a Dog’s, do not fall out altogether, as in the Bear. In the Pliocene, or Late Miocene strata, remains have been found of many existing genera, such as Cats, Civets, Hyænas, Dogs, Weasels, Ratels, and Otters; but amongst these are several genera not occurring in any of the more recent strata, and all, or nearly all, tending to bridge over the gaps which separate existing families from one another. For instance, a perfect gradation between the Hyænas and Civets is afforded by two genera, _Hyænictis_ and _Ictitherium_; while _Lutrictis_ shows affinities both with Civets and Otters, _Hemicyon_ with Dogs and Gluttons, and _Dinictis_ with Cats and Weasels. Another very interesting genus, _Promephitis_, belongs undoubtedly to the Weasel family, but is intermediate between its three sub-families, the Weasels proper, Badgers, and Otters. _Simocyon_, again, an animal about the size of a Leopard, is described as having the canines of a Cat, the molars of a Dog, and jaws shaped like those of a Bear. Lastly, _Amphicyon_ is a large plantigrade animal, Bear-like for the most part, but with trenchant molars, like a Dog’s, and having a small additional or third molar on each side of the lower jaw, the number of its teeth being thus brought up to that which may be called the typical Mammalian number, namely, forty-four.[197] [Illustration: SKULL OF ARCTOCYON. (_After Gaudry._)]