1911 Encyclopædia Britannica/Pecora
PECORA (plural of Lat. pecus, cattle), a term employed—in a more restricted sense—in place of the older title Ruminantia, to designate the group of ruminating artiodactyle ungulates represented by oxen, sheep, goats, antelopes, deer, giraffes, &c.
The leading characteristics of the Pecora are given in some detail in the article Artiodactyla (q.v.); but it is necessary to allude to a few of these here. Pecora, or true ruminants as they may be conveniently called, have complex stomachs and chew the cud; they have no upper incisor teeth; and the lower canines are approximated to the outer incisors in such a manner that the three incisors and the one canine of the two sides collectively form a continuous semicircle of four pairs of nearly similar teeth. In the cheek-teeth the component columns are crescent-shaped, constituting the selenodont type. In the forelimbs the bones corresponding to the third and fourth metacarpals of the pig's foot are fused into a cannon-bone; and a similar condition obtains in the case of the corresponding metatarsals in the hind-limbs. There is generally no sagittal crest to the skull; and the condyle of the lower jaw is transversely elongated. Another general, although not universal, characteristic of the Pecora is the presence of simple or complex appendages on the forehead commonly known as horns. In a few existing species, such as the musk-deer and the water-deer, these appendages are absent, and they are likewise lacking in a large number of extinct members of the group, in fact in all the earlier ones. They are, therefore, a specialized feature, which has only recently attained its full development.
These horns present several distinct structural types, which may be classified as follows:—
I. The simplest type is that of the giraffe, in which three bony prominences—a singie one in front and a pair behind—quite separate from the underlying bones and covered during life with skin, occupy the front surface of the skull. The summits of the hind pair are surmounted by bristly hairs. In the extinct Sivatherium there are two pairs of such appendages, of which the hinder are large and were probably covered during life either with skin or thin horn. In the giraffes the separation of the horns from the skull may be a degenerate character.
Fig. 1.—Head of Siamese Deer (Cervus schomburgkis), showing antlers.
II. In the Asiatic muntjac deer we find a pair of skin-covered horns, or “pedicles,” corresponding to the paired horns of the giraffe, although welded to the skull. From the summits of these pedicles arise secondary outgrowths, at first covered with skin, which (owing to the growth of a ring of bone at the base arresting the flow of blood eventually dries up and leaves bare bone incapable of further growth. In the muntjac the bare bony part, or “antler,” is small in proportion to the skin-covered pedicle, and simple in structure; but in the majority of deer the antler increases in size at the expense of the pedicle—which dwindles—and in some species, like the Siamese deer (fig. 1), the sambar and the red deer, becomes very large and more or less branched. Owing to liability to necrosis, the permanent retention of such a mass of dead bone would be dangerous; and the antlers are consequently shed annually (or every few years), to be renewed the following year, when, till the animal becomes past its prime, they are larger than their predecessors. The periodical shedding is also necessary in order to allow of this increase in size. With the exception of the reindeer, antlers are confined to the malcs.
III. The third type of horn is presented by the American prong buck, 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. The sheaths are akin to hair in structure, thus suggesting affinity with the hairs surmounting the giraffe's horns. Female prong buck may or may not have horns.
IV. In the great majority of “Hollow-horned Ruminants,” such as oxen, sheep, goats and antelopes (fig. 2), the horny sheath (or true “horn”) forms a simple unbranched cone, which may be compressed, spirally twisted, or curved in one or more directions, but is permanently retained and continues to grow throughout life from the base, while it becomes worn away at the tip. Rarely, as in the four-horned antelope, there are two pairs of horns. In many cases these horns are present in both sexes.
Dr H. Gadow is of opinion that the antlers of the deer, the horn-like protuberances on the skull of the giraffe, and the true horns of the prong buck 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. This arrangement has the disadvantage of separating the deer from the giraffes, to which they are evidently nearly related; but Dr Gadow's work brings them more into line. Whether he is right in regarding the hollow-horned ruminants as derived from the primitive deer may, however, be a matter of opinion. One very important fact recorded by Dr Gadow is that calves and lambs shed their horns at an early age. 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 above-mentioned four types of skull appendages are generally regarded as severally characteristic of as many family groups, namely the Giraffidae, Cervidae, Antilocapridae and Bovidae. The two last are, however, much more closely connected than are either of the others, and should perhaps be united.
Giraffidae.—In the Giraffidae, which include not only giraffes (Giraffa) but also the okapi (Ocapia) and a number of extinct species from the Lower Pliocene Tertiary deposits of southern Europe, Asia and North Africa, the appendages on the skull are of type No I., and may well be designated “antler-horns.” Another important feature is that the lower canine has a cleft or two-lobed crown, so that it is unlike the incisors to which it is approximated. There are no upper canines; and the cheek-teeth are short-crowned (brachyodont) with a peculiar grained enamel, resembling the skin of a slug in character. The feet have only two hoofs, all traces of the small lateral pair found in many other ruminants having disappeared.
The giraffes (Giraffa) are now an exclusively African genus, and have long legs and neck, and three horns—a single one in front and a pair behind—supplemented in some instances with a rudimentary pair on the occiput.
Fig. 2.—Head of Grant's Gazelle (Gazella granti), showing horns.
The okapi (Ocapia), which is also African but restricted to the tropical forest-region, in place of being an inhabitant of more or less open country, represents a second genus, characterized by the shorter neck and limbs, the totally different type of colouring, and the restriction of the horns to the male sex, in which they form a pair on the forehead; these horns being more compressed than the paired horns of the giraffe, and penetrating the skin at their summits (see Giraffe and Okapi). Remains of extinct species of giraffe occur in the Lower Pliocene formations of Greece, Hungary, Persia, Northern India and China. From deposits of the same age in Greece, Samos and elsewhere have been obtained skulls and other remains of Palaeotragus or Samotherium, a ruminant closely allied to Ocapia, the males of which were armed with a very similar pair of dagger-shaped horns. Helladotherium was a much larger animal, known by a single hornless skull from the Pliocene of Greece, which may be that of a female. In the equally large Bramatherium and Hydaspitherium of India the horns of the males were complex, those of the former including an occipital pair, while those of the latter arise from a common base. In both genera, as in the okapi, there is a vacuity in front of the orbit. Largest of all is Sivatherium, typically from the Lower Pliocene of Northern India, but also recorded from Adrianople, in which the skull of the male is short and wide, with a pair of simple conical horns above the eye, and a huge branching pair at the vertex. Libytherium is an allied form from North Africa. Whether the Giraffidae were originally an African or a Euro-Asiatic group there is not yet sufficient evidence to decide. The family is unrepresented in the western hemisphere.
Fig. 3.—Skull of Chinese Water-Deer, Hydrelaphus inermis (adult male), a Deer without Antlers, but with largely developed upper canine teeth.
Cervidae.—In the deer-tribe, or Cervidae, the lower canine, as in the two following families, is simple and similar to the incisors. The frontal appendages, when present, are confined (except in the case of the reindeer) to the males, and take the form of antlers, that is to say of type No. II. in the foregoing description. As a general rule, the molars, and more especially the first, are partially brachyodont (short-crowned), although they are taller in the chital (Cervus axis). In the skull there are two orifices to the lachrymal duct, situated on or inside the rim of the orbit. A preorbital vacuity of such dimensions as to exclude the lachrymal bone from articulation with the nasal. Upper canines usually present in both sexes, and sometimes attaining a very great size in the male (see fig. 3). Lateral digits of both fore and hind feet almost always present, and frequently the lower ends of the metacarpals and the metatarsals as well. Placenta with few cotyledons. Gall-bladder absent (except in the musk-deer, Moschus). This family contains numerous species, having a wide geographical distribution, ranging in the New World from the Arctic circle as far south as Patagonia, and in the Old World throughout the whole of Europe and Asia, but absent in Africa south of the Sahara, and, of course, Australasia. Evidently the family originated in the northern continent of the Old World, from which an entrance was effected by way of Bering Strait into America. Some of the more northern American deer, such as the wapiti, reindeer and elk (moose), are closely allied to Old World species, but there is also a group of exclusively American deer (Mazama)—the only one found in Central and South America—the members of which are unlike any living Old World deer, and these must be regarded as having reached the western hemisphere at an earlier date than the wapiti, reindeer and elk (see Deer, Elk, Fallow-Deer, Muntjac, Musk-Deer, Père David's Deer, Reindeer, Roebuck, Water-Deer, &c.).
Remains of deer more or less nearly allied to species inhabiting the same districts are found over the greater part of the present habitat of the family. It is noteworthy, however, that certain Pliocene European deer (Anoglochis) appear to be closely allied to the modern American deer (Mazama). As we descend in the geological series the deer have simpler antlers, as in the European Miocene Dicrocerus; while in the Oligocene Amphitragulus, Dremotherium and Palaeomeryx, constituting the family Palaeomerycidae, antlers were absent, and the crowns of the molars so low that the whole depth of the hollows between the crestentic columns is completely visible. Most of these animals were of small size, and many had long upper canines, like those of the existing Hydrelaphus; while in all there was no depression for a gland in front of the eye.
From North America have been obtained remains of certain ruminants which seem in some degree intermediate between deer and the prongbuck. Of one of these a complete skeleton was obtained in 1901 from the Middle Miocene deposits of north-eastern Colorado, and as mounted stands 19 in. in height at the withers. With the exception that the right antler is malformed and partially aborted, and that the bones of the lateral toes have been lost, the skeleton is practically complete. The one complete antler has a well-marked burr and a long undivided beam, which eventually forks. After this there is a bifurcation of the hinder branch, thus producing three tines. From the presence of these well-marked antlers the skeleton would at first sight be set down as that of a small and primitive deer, conforming in regard to the structure of these appendages to the American type of the group. Mr W. D. Matthew shows, however, that the skeleton of Merycodus, as the extinct ruminant is called, differs markedly from that of all deer. 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. In the absence of any trace of the lower extremities of the metacarpal and metatarsal bones of the lateral toes the skeleton differs from the American deer, and resembles those hollow-horned ruminants in which these toes persist.
As a whole Merycodus presents a curious mixture of cervine and antilopine character. To explain these, two alternatives are offered by the describer. 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. The former alternative, it is urged, involves a parallelism too close and too uniform between unrelated types to have been probable. 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. If, therefore, Antilocapra deserves to be separated as a family from the Bovidae, the same can scarcely be refused for Merycodus. 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. As a temporary measure it seems preferable to regard Merycodus either as representing a distinct subfamily of Antilocapridae or a family by itself, the latter course being adopted by Mr Matthew.
Whatever be the ultimate verdict, the association of antlers—and these, be it noticed, conforming almost exactly with the forked type characteristic of American deer—with an antilopine type of skull, skeleton and teeth in Merycodus is a most interesting and unexpected feature. Merycodus was named many years ago by Professor J. Leidy on the evidence of imperfect materials, and other remains now known to belong to the same type were subsequently described as Cosoryx, to which Blastomeryx seems to be allied. Not till the discovery of the skeleton of the species described by Mr Matthew was it possible to arrive at an adequate conception of the affinities of this remarkable ruminant.
Antilocapridae.—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—Antilocapridae. 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 cheek teeth are tall-crowned (hypsodont), and lateral hoofs are wanting (see Prongbuck).
Bovidae.—Lastly, we have the great family of hollow-horned ruminants or Bovidae, in which the horns (present in the males at least of all the existing species) take the form of simple non-deciduous hollow sheaths growing upon bony cores. As a rule the molars are tall-crowned (hypsodont). lfsually only one orifice to the lachrymal canal, situated inside the rim of the orbit. Lachrymal bone almost always articulating with the nasal. Canines absent in both sexes. The lateral toes may be completely absent, but more often are represented by the hoofs alone, supported sometimes by a very rudimentary skeleton, consisting of mere irregular nodules of bone. Lower ends of the lateral metacarpals and metatarsals never present. Gall-bladder almost always present. Placenta with many cotyledons.
The Bovidae form a most extensive family, with members widely distributed throughout the Old World, with the exception of the Australian region; but in America they are less numerous, and confined to the Arctic and noithern temperate regions, no species being indigenous either to South or Central America. The home of the family was evidently the Old World, whence a small number of forms made their way into North America by way of what is now Bering Strait. It has already been pointed out that the Cervidae originated in the northern continent of the Old World; and it has been suggested that the Bovidae were developed in Africa. Unfortunately, we know at present practically nothing as to the past history of the group, all the fossil) species at present discovered approximating more or less closely to existing types. While admitting, therefore, that there are several facts in favour of the theory of an African origin of the Bovidae, final judgment must for the present be suspended. For the various generic types see Bovidae, and the special articles referred to under that heading. (R. L.*)