Fig. 268.—Skull of false †sabre-tooth (†Nimravus gomphodus) from the John Day. (After Matthew.) p. 4 = fourth upper premolar, sectorial.
Also in the John Day stage lived †Archælurus and †Nimravus, which, as was noted above ([p. 249]), have been called the “false sabre-tooths,” for in them the upper canine was not much larger than the lower and the latter, though smaller than in the felines, was yet very much less reduced than in the true †machairodonts. The skull closely resembled that of †Dinictis, but the lower jaw was without flanges. The limbs were long and slender and the feet long and digitigrade. The pes had only four digits, of which the median pair was elongated and the lateral pair shortened, so as to produce considerable resemblance to the pes of the dogs, and the claws were partially retractile. The proportions of the body, limbs and feet were suggestively like those of the Cheeta, or Hunting Leopard (Cynælurus jubatus) of India, the generic name of which means “dog-cat,” and it is quite possible that the Cheeta may have been derived from some member of this “false †sabre-tooth” series, though the connecting links are unknown. These cursorial cats quite displaced the leaping †machairodonts of the †Hoplophoneus type, at least in the Oregon region at a time when, it will be remembered, that region had a remarkable variety of dogs. In other parts of the continent, of which we have no record, the true †machairodonts must have been thriving, as may be inferred from their comparative abundance in the later formations.
Concerning the habits of these cursorial cats, Professor Merriam says: “When the canines are not developed to the dagger-like form for stabbing, the premolar teeth serve a more definite purpose in the destruction of prey and would be less subject to reduction. The view suggested above finds support in that such evidence as we have indicates that during the deposition of the Middle John Day beds this region was in the main a country of open plains, offering advantages to running types of carnivores, and that during this epoch the Archælurus-Nimravus type of feline was by far the most common form [i.e. of cats].” The derivation of these cats is still obscure, but their likeness to certain forms of the European Oligocene suggests that they were immigrants.
The true cats of the subfamily Felinæ include the great variety of living forms, large and small, from the Lion and Tiger at one extreme to the Domestic Cat at the other. There is great difference among naturalists with regard to the nomenclature of the Recent cats; some make a considerable number of separate genera, while others include all the species, except the lynxes and the Cheeta, in the genus Felis. For the purposes of this book the latter practice is the more convenient and will be followed. In Felis the dental formula is: i 3/3, c 1/1, p 2-3/2, m 1/1, × 2 = 28-30; the canines are large and strong, of oval section, and the upper one is but little larger than the lower; there are two large and functional premolars in each jaw, and an additional very small one may or may not be present in the upper jaw. The upper sectorial has a large shearing blade, with well-developed anterior accessory cusp, and the inner cusp, which in †Smilodon had almost disappeared, is quite large and carried on a separate root. The lower sectorial is composed of two cusps only, all traces of the heel and of the inner cusp having disappeared. The single upper molar is very small and usually concealed by the sectorial. The skull is very short and broad, and the shortening of the jaws gives great power to the biting muscles, because of the more favourable leverage. The zygomatic arches are very stout and curve out boldly, contributing much to the rounded shape of the head; the orbits are almost encircled in bone. The large tympanic bullæ are two-chambered and there is no alisphenoid canal, but in several other respects the base of the cranium differs markedly from that of †Smilodon. The lower jaw is without flanges and there is no angle between front and sides.
Fig. 269.—Dentition of Lynx (L. rufus), left side. i. 3, external upper incisor. i. 1, first lower incisor. c. = canine. p. 3, p. 4, third and fourth premolars. m. 1, first molar.
Fig. 270.—Upper teeth of Puma (Felis concolor), left side. p. 4, fourth premolar. m. 1, first molar.
The neck is short, the body long and the tail is long in most of the species, but short in the lynxes. The limbs are relatively longer and less massive than in †Smilodon, and there are five toes in the manus, four in the pes; the claws are hooded and retractile.