In the newest, that is the most recently deposited, set of strata, those which together form the beds of the Pleistocene period, we find a very curious change in the flesh-eaters inhabiting England. Instead of having nothing but Wild Cats, Wolves, and Bears—the only wild beasts known to have existed in the historical period—we have the enormous Cave Lion (Felis spelæa), besides the Cave Bear (Ursus spelæus), and the Cave Hyæna (Hyæna spelæa), the last being merely a variety of the Spotted Hyæna (Hyæna crocuta) of the present day. The presence of the first and last of these would seem to indicate that the climate of Britain was warmer in the Pleistocene period than it now is; but the presence of the Glutton, as well as of some non-carnivorous Arctic animals, tends to the other opinion, namely, that the climate of England was sub-Arctic. Very probably the Cave Lion and Hyæna were provided with thick woolly fur, and so, like the Mantchurian Tiger and the Northern Leopard (see [pp. 34] and [42]), enabled to bear a degree of cold experienced by but few of their relatives at the present day.
SKULL OF MACHÆRODUS. (After Gaudry.)
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]
SKULL OF ARCTOCYON. (After Gaudry.)
In the Eocene, or Lower Tertiary, still more remarkable forms occur, along with several genera existing at the present day, such as the Cryptoprocta, Civet, Dog, and Marten, all of which are found in the upper or more recent strata of the Eocene formation. But lower down the genus Cynodon also connects Dogs with Civets; and in the very lowest beds occurs a large plantigrade animal (Arctocyon), with a very small brain-case, wide jugal arches, a complete set of forty-four teeth, and altogether of a generalised character. In the Eocene of North America, Limnocyon and Prototomus occur low down, and in the Middle Eocene a form as large as a Lion has been discovered, to which the name Limnofelis has been given, and also Orocyon, and some allies of the Hyænodon.
