Fig. 149.—Lama. Lama huanacos. × 1⁄12.
Extinct Camels.—The earliest cameloid type is the genus Protylopus,[[186]] of which we are acquainted with an imperfect skull
and the greater part of a radius and ulna belonging to one individual, and most portions of the hind-limbs in other specimens. The one species, P. petersoni, was about the size of a "jack rabbit," and is late Eocene (Uinta formation) and American in range. The teeth of this mammal are the typical forty-four, and the canines are not pronounced, being incisiform in shape. In the skull the nasals overhang, as in the genus Poebrotherium. The orbit is not closed by bone. There is in this ancient Camel a trace of the supra-orbital notch so characteristic of the Camel tribe. "The vertebrae resemble those of the modern Lamas closely in their general proportions." The lumbars have the usually Cameloid formula of 7. This genus has but two functional toes on the hind-feet, the second and fifth being reduced to vestiges. It is interesting to note that the radius and ulna appear to remain distinct, except in very old animals, in which they come to be co-ossified in the middle only, thus foreshadowing their complete union in the next genus, Poebrotherium. The present genus, moreover, as well as Poebrotherium, was distinctly unguligrade; it has not acquired the characteristic phalangigrade mode of progression of the modern types of Camels.
Fig. 150.—Skull of Poebrotherium wilsoni. i1, i2, i3, Incisors 1-3. × ½. (After Wortman.)
The American and Oligocene Poebrotherium has been recently and exhaustively studied by Professor Scott.[[187]] It was considerably smaller than a Lama. Its neck was long as compared with other Artiodactyles, but still shorter than that of the Lama. It was a lightly-built, graceful creature, with apparently some external likeness to a Lama. It is an important fact to notice that at this
period, and for a long time after, there were no types referable to the Camelidae in the Old World. Though a Camel in many features of its organisation, Poebrotherium was "generalised" in many ways. Thus the metacarpals and metatarsals were not fused to form a cannon bone, and the two lateral digits were represented by splint rudiments of metacarpals and metatarsals. The dentition was complete. The skull though distinctly Tylopodan, also shows more generalised characters. Thus the orbit is not quite, though nearly, completed by bone. In the Camel it is quite closed. The nasal bones are much longer, reaching nearly to the end of the snout. The odontoid process of the axis vertebra is not spout-like as in existing forms, but cylindrical, though slightly flattened upon the upper surface. The scapula is described as being more like that of the Lama than of the Camel, though variations occur which approximate to the Camel. The brain, judging of course from casts, has those sulci "which are common to the whole series of Ungulates, and closely resemble those of a foetal Sheep."
Fig. 151.—Anterior surface of axis of Red Deer, × ⅔. o, Odontoid process; pz, posterior zygapophysis; sn, foramen for second spinal nerve. (From Flower's Osteology.)
Later in historical sequence than Poebrotherium, and structurally intermediate between it and Protolabis, is the Miocene genus Gomphotherium. It shows an advance in structure upon Poebrotherium, in that the orbit is completely encircled by bone, though the posterior wall is thin; the lower canines instead of being incisiform are curved back as in later Camels, and separated by a wide diastema from the preceding and the succeeding teeth.