The group at the present day is divided into Girafjidae (giraffe and okapi), Cervidae (deer), Antilocapridae (prongbuck), and Bovidae (oxen, sheep, goats, antelopes, &c.).
No true antelopes are American, the prongbuck (Antilocapra), which is commonly called "antelope" in the United States, representing a distinct group; while, as already mentioned, the Rocky Mountain or white goat stands on the borderland between antelopes and goats.
Coyotes are creatures of slinking and stealthy habits, living in burrows in the plains, and hunting in packs at night, when they utter yapping cries and blood-curdling yells as they gallop. Hares ("jack-rabbits"), chipmunks or ground-squirrels, and mice form a large portion of their food; but coyotes also kill the fawns of deer and prongbuck, as well as sage-hens and other kinds of game-birds.
When hunting antelope (prongbuck) and deer the coyotes spread out their pack into a wide circle, endeavouring to surround their game and keep it running inside their ring until exhausted.
The third type of horn is presented by the American prongbuck, or pronghorn, in which bony processes, or " cores," corresponding to the horns of the giraffe, have acquired a horny sheath, in place of skin; the sheath being in this instance forked, and annually shed and renewed, although the core is simple.
Female prongbuck may or may not have horns.
Gadow is of opinion that the antlers of the deer, the hornlike protuberances on the skull of the giraffe, and the true horns of the prongbuck and other hollow-horned ruminants (Bovidae) are all different stages of evolution from a single common type: the antlers of the deer being the most primitive, and the horns of the Bovidae the most specialized.
From the fact that the bony horn-core of the hollow-horned ruminants first develops as a separate ossification, as do the horns of the giraffe, while the pedicle of the antlers of the deer grow direct from the frontal bone, it has been proposed to place the hollow-horned ruminants (inclusive of the prongbuck) and the giraffes in one group and the deer in another.
The Bovidae are thus brought into nearer relationship with the American prongbuck (the only living ruminant which sheds its horn-cover in the adult condition) than has generally been supposed.
The most noteworthy point of distinction is in the skull, in which the facial portion is sharply bent down on the posterior basal axis in the fashion characteristic of the hollow-horned ruminants (oxen, antelopes, &c.), and the American prongbuck, instead of running more or less nearly parallel to the same, as in deer.
Again, the cheek-teeth have the tall crowns characteristic of a large number of representatives of the first group and of the prongbuck, thereby showing that Merycodus can scarcely be regarded as a primitive type.
As regards the general structure of the rest, of the skeleton, it must suffice to say that this agrees closely with that of the antelopes and the prongbuck, and differs markedly from the cervine type.
Either we must regard Merycodus as a deer which parallels the antelopes and the prongbuck in every detail of skeletal structure, or else, like the prongbuck, an antelope separated from the main stock at a date sufficiently early to have permitted the development of a distinct type of cranial appendages, namely, antlers in place of true horns.
On the latter view Merycodus, the prongbuck (Antilocapra) and the antelopes must be regarded as representing three branches from an original common stock, divergent as regards the structure of their cranial appendages, but parallel in other respects.
But American extinct types appear to indicate signs of intimate relationship between antelopes, prongbuck and deer, and it may be necessary eventually to amend the current classification.
By many modern writers the American prongbuck, pronghorn or " antelope," alone forming the genus Antilocapra, is regarded as representing merely a sub-family of the Bovidae, to which latter group the animal is structurally akin.
In view of what has been stated in the preceding paragraph with regard to the extinct American genus Merycodus, it seems, however, at least provisionally advisable to allow the prongbuck to remain as the type of a family - A ntilocapridae.
The characteristic of this family - as represented by the prongbuck - is that the sheath of the horns is forked, and shed annually, or every few years.
The Antilocapridae (prongbuck), whose relationships appear to be rather with the Cervidae than with the Bovidae, are on the other hand apparently a North American group. The chevrotains (Tragulidae), now surviving only in West and Central Africa and tropical Asia, are conversely a purely Old World group.