Fig. 209.—Lower Miocene †giraffe-camel (†Oxydactylus longipes). Restored from a skeleton in the Carnegie Museum, Pittsburgh.
In the lower Miocene the †giraffe-camels were represented by the genus †Oxydactylus, which was a considerably smaller animal than its successor †Alticamelus, of the middle Miocene and later formations, and had shorter neck and legs. The teeth, though brachyodont, were not very low-crowned. There was no cannon-bone, the two metapodials of each foot remaining separate. An especially noteworthy feature in this genus is to be observed in the character of the hoofs, which, as the ungual phalanges demonstrate, were narrow and pointed, like those of antelope and deer, and carried most of the weight. The member of the grazing series (†Protomeryx) was smaller in every way than its contemporary (†Oxydactylus) of the browsing line and had shorter neck and legs, though these were already long. The teeth were present in undiminished number, and the grinders, while not properly to be called hypsodont, showed a decided tendency to assume that character. The feet were in the same stage of development as in †Oxydactylus, that is to say, with two free digits and pointed, deer-like hoofs. We have thus the remarkable and most significant fact that, while the grazing and browsing camels of the lower Miocene were already distinctly separated, neither had yet attained to the type of foot-structure which both of them afterwards independently acquired. This is a very instructive example of parallel evolution in closely related series.
Fig. 210.—Skeleton of †Oxydactylus longipes. Lower Miocene. (After Peterson.) For restoration, see [Fig. 209].
Of still another phylum of the camel family, the lower Miocene contains the only representatives yet discovered, the little “†gazelle-camels,” as they may be called. The single known genus (†Stenomylus, [Fig. 131, p. 242]) of this series was quite a small animal, much smaller than its contemporaries of the grazing or browsing series. †Stenomylus was an extremely slender, cursorial creature and had a very exceptional feature in its dentition in the apparent presence of ten lower incisors, five on each side, the canine and first premolar having assumed the form and functions of the incisors; the molars were low-crowned. The head was rather small and rounded, the neck long and light, the limbs and feet elongate and excessively slender. The feet had two digits each, which were separate, not forming a cannon-bone, and the hoofs were narrow, pointed and deer-like. These delicate and graceful little animals had but a brief career, which seems to have reached its close in the lower Miocene. Perhaps their complete defencelessness made it impossible for them to maintain themselves against their enemies, despite their evident capacity for swift running.
The camels of the upper Oligocene (John Day) are still incompletely known, but appear all to have belonged to the series of grazers which led up to the modern genera. Future discovery may bring to light in the John Day earlier members of the †giraffe-camel series, of which a possible member is found in the uppermost substage of the White River, or perhaps both phyla united in the upper Oligocene, a question which remains to be determined. At all events, in the middle substage of the White River, or lower Oligocene, there is no evidence of more than a single phylum, from which the others were almost certainly derived, branching off from the main stem at different levels. First was given off the branch of the †giraffe-camels, then (or perhaps even earlier) that of the little †gazelle-camels, and, finally, the main stem bifurcated into the two phyla of the llamas and the true camels. The point of origin of the †gazelle-camels is still uncertain.
