CHAPTER XV

HISTORY OF THE PRIMATES

This order embraces the lemurs, monkeys, man-like apes and Man, though in the general account Man will be omitted from consideration. The Primates are clothed in dense fur or shaggy hair. The teeth are always low-crowned and rooted and reduced in number, the incisors generally to 2/2 and the premolars to 3/3-2/2; the molars are trituberculate or quadrituberculate. The cranium is unusually capacious and the orbit is entirely encircled in bone. The tail varies much in length and may be entirely wanting. The bones of the fore-arm and lower leg are separate and the radius has much freedom of rotation, in correspondence with the grasping power of the hand. The pes is also a grasping organ and, with few exceptions, the thumb and great toe are opposable to the other digits; the bones of the wrist do not coössify and frequently the central is present. The feet are plantigrade and almost always pentadactyl and, with a few exceptions, have neither claws nor hoofs, but flat nails; the ungual phalanges are correspondingly modified and do not taper toward the free end, but expand at the tip. The Primates are characteristically arboreal in habit, but a few, such as the baboons, have become secondarily adapted to a terrestrial mode of life. They inhabit at present all the tropical regions of both hemispheres, Australia excepted. Extra-tropical North America has no existing member of the order and, so far as we know, has had none since the Eocene epoch. The most important of the genera of the western hemisphere are listed below.

Suborder LEMUROIDEA. Lemurs

I. †NOTHARCTIDÆ.

_†Pelycodus_, low. and mid. Eoc. _†Notharctus_, Eoc.

II. †ANAPTOMORPHIDÆ.

_†Anaptomorphus_, low. and mid. Eoc. _†Omomys_, mid. Eoc. _†Hemiacodon_, do.

Suborder ANTHROPOIDEA. Monkeys, Apes, Man

Section PLATYRRHINA

III. HAPALIDÆ. Marmosets.

_Hapale._ Pleist. and Rec. _Midas_, Rec.

IV. CEBIDÆ. South American Monkeys.

_Cebus_, Pleist. and Rec. _Alouatta_, Howling Monkeys, Pleist. and Rec. _Ateles_, Spider Monkeys. _Pithecia_, Sakis. _Cacajao_, Uakaris. _Nyctipithecus_, Douroucoulis. _†Eriodes_, Pleist. _†Homunculus_, Santa Cruz. _†Pitheculus_, do.

The existing Primates are divided into two suborders, Lemuroidea and Anthropoidea, which are quite clearly distinguished from each other, but the fossil forms largely efface the distinction.

SUBORDER LEMUROIDEA. LEMURS

The name _Lemur_, which Linnæus gave to a genus of this suborder, signifies in Latin a spectre or ghost and was probably suggested by the very strange appearance and nocturnal habits of these curious creatures. The term has been adopted as the English name for the group, as there was no vernacular word for it. The lemurs are very obviously the more primitive division of the Primates. Omitting for the present the extinct forms, the dental formula is usually: _i_ 2/2, _c_ 1/1, _p_ 3/3, _m_ 3/3, × 2 = 36; the upper canine is a long, sharp, dagger-like tooth, but the lower one, in nearly all of the genera, is like an incisor and its place is taken by the anterior premolar; the premolars are simple, compressed and trenchant and the upper molars tritubercular. The skull usually has a long and tapering facial portion, so that the living head has some resemblance to that of a raccoon. The orbits almost always have a more or less lateral presentation, instead of being directed forward, as they are in the Anthropoidea; they are encircled in bone, but are not walled in by a bony funnel; the lachrymal bone is extended on the face and the foramen is outside of the orbit. The hind legs are longer than the fore; the humerus retains the epicondylar foramen and the femur has a third trochanter; the feet are plantigrade, almost always five-toed, with opposable thumb and great toe, and having a varying proportion of flat nails and sharp claws. The brain is of a primitive type and not much convoluted.

All the existing and most of the fossil lemurs are small animals, some quite minute, and only in the Pleistocene of Madagascar have large ones been found. They are chiefly nocturnal and arboreal in habits, and feed upon fruit and leaves, but vary their diet with insects, small reptiles, birds and eggs. Their present geographical distribution is very remarkable; more than two-thirds of the existing species are confined to Madagascar; the others are in tropical Africa, southern Asia and the Asiatic islands, as far east as Celebes and the Philippines. In the Eocene epoch they extended all over the northern hemisphere, but have not been found in any subsequent formation outside of their present range.

Lemurs occurred in the Uinta stage, but were much more abundant in the Bridger, of which the best-known genus is _†Notharctus_. These Eocene forms did not have the aberrant peculiarities of the modern lemurs, but departed less from the primitive stock common to both of the suborders. In _†Notharctus_ the dental formula was: _i_ 2/2, _c_ 1/1, _p_ 4/4, _m_ 3/3, × 2 = 40, the dentition being reduced only to the extent of losing one incisor on each side above and below; the lower canine was not incisiform nor had the anterior premolar taken its place; the upper molars were quadritubercular, and in the lower ones the anterior triangle was hardly higher than the heel. The two halves of the lower jaw were coössified at the symphysis, and the femur had lost the third trochanter. It is not likely that _†Notharctus_ was ancestral to any of the existing lemurs, but may have been to the numerous forms of the European upper Eocene.

The Wasatch genera are known from very fragmentary material, but it suffices to show that some of the genera, at least (_e.g._ _†Pelycodus_), were decidedly more primitive than those of the Bridger. The incisors had already been reduced to 2/2, the well-nigh universal formula among the Primates; the upper molars were tritubercular, but with a minute fourth cusp beginning to appear, and in the lower molars the anterior triangle was elevated above the heel. The two halves of the lower jaw were separate.

The Paleocene has yielded nothing that can be positively referred to the Primates, but there was a group of genera (_e.g._ _†Indrodon_), known only from jaws and teeth, which have been variously assigned to the lemurs and the Insectivora and may have belonged to either order, or have represented the transition between them. This very uncertainty is in itself a significant fact, for it is another of the many examples of the way in which, at that early period, the mammalian orders were so approximated that it is often very difficult to distinguish them.

It was stated above that the distinction between existing lemurs and anthropoids was a very clear one, but to this statement there is one partial exception. The curious little Tarsier (_Tarsius spectrum_), an animal about the size of the Grey Squirrel, an inhabitant of the Malay Archipelago, is thus described by Mr. Beddard: “The ears are large and the eyes are extraordinarily developed. The fingers and toes terminate in large, expanded disks and are furnished with flattened nails, except on the second and third toes, which have claws. The tail is longer than the body and tufted at the end.... The Tarsiers are nocturnal and particularly arboreal; they live in pairs, in holes in tree stems and are mainly insectivorous in their food.... Like so many Lemurs, this animal is held in superstitious dread, which is the result of its most weird appearance.”[13] The skull is more anthropoid in character than is that of any other lemur, the face being greatly shortened, the cranium enlarged and the orbit not merely encircled in a bony rim, but with a thin posterior wall of bone. There are also structural features in the soft parts, which are more anthropoid than lemuroid.

[Illustration: FIG. 285.—Head of monkey-like lemur (_†Anaptomorphus homunculus_) from the Wasatch. Restored from a skull in the American Museum.]

The particular interest which _Tarsius_ possesses for the student of American mammals is its resemblance to the Wasatch genus _†Anaptomorphus_, the type of a family which was abundant and varied in the lower and middle Eocene. This genus was remarkably advanced in view of its great antiquity. The dental formula was: _i_ 2/2, _c_ 1/1, _p_ 3/3-2, _m_ 3/3, × 2 = 34-36; in the upper jaw the premolars were bicuspid and the molars tritubercular, while the lower premolars were simple. The face was very much shortened; the orbits were very large and encircled in bone, but without the posterior wall. This produces a decided likeness to the Tarsier and is no doubt indicative of nocturnal habits. The cranium was remarkably large, and no other Wasatch animal had a brain-case so capacious in proportion to its size. A lemurine character was the position of the lachrymal foramen outside of the orbit. The two halves of the lower jaw were separate. It is hardly likely that these American lemurs were the actual ancestors of the anthropoids, but they closely represent what those ancestors must have been.

SUBORDER ANTHROPOIDEA. MONKEYS, APES, MAN

The specifically human characters will be omitted in defining the suborder. The Anthropoidea are plantigrade, usually arboreal and pentadactyl, with opposable thumb and great toe and thus the pes is like a hand, hence the term “Quadrumana” formerly given to the apes and monkeys. Except in the South American marmosets (Hapalidæ) all of the digits have nails. The canines are generally more or less tusk-like, projecting above (or below) the level of the other teeth; the premolars mostly have two tubercles, like the human bicuspids, the upper molars have three, or more commonly four, cusps and the lower, four or five. Save in the baboons, the skull has a very short muzzle and a very large cranium, the capacity of which is relatively greatest in the large apes; the brain is large and complexly convoluted. The orbits present directly forward and are deep, funnel-shaped cavities for the lodgment of the eyeballs, a thin bony wall completely enclosing them externally and posteriorly. The lachrymal bone and its foramen are within the edge of the orbit; the nasal bones are short and have a nearly vertical position. The two frontal bones are early fused into one and usually there is no sagittal crest; the two halves of the lower jaw are coössified at the symphysis. The tail is extremely variable in length and may be three times as long as the body, or entirely absent. The fore and hind legs are sometimes of nearly equal length, but far more frequently the anterior pair are much the longer. The length of the legs in proportion to that of the body is very different in the different families. The humerus is much like that of Man and has no epicondylar foramen; the radius has a very complete movement of rotation; the femur never has the third trochanter and the lower leg bones are always separate. The thumb is more or less opposable to the other digits, except in the marmosets, but never so perfectly as in Man; the great toe is also opposable, but shorter than the other digits.

The Anthropoidea are divisible into two sections, the Catarrhina, characteristic of the Old World, and the Platyrrhina, confined to the New. In the Catarrhina, or Old World apes and monkeys, the dental formula is the same as in Man: _i_ 2/2, _c_ 1/1, _p_ 2/2, _m_ 3/3, × 2 = 32; the nostrils are close together and the tympanic bullæ have tubular entrances. Many, but not all, have cheek-pouches opening into the mouth. The tail is never prehensile and, except in most of the large, man-like apes (Simiidæ), there are naked callosities on the buttocks. With these Old World forms we have no further concern, though it may be noted in passing that Dr. Schlosser has discovered in the Oligocene of Egypt certain monkeys (_†Parapithecus_) which he thus describes: “The number and structure of the teeth, character of the jaws and bodily size make complete the transition from the Anaptomorphids and Tarsiids to the Simiids.”

_Section Platyrrhina. South American Monkeys_

In these animals the nostrils are separated by a broad septum, and there are always three premolars above and below (_p_ 3/3). The tail is frequently prehensile and serves as a fifth limb, being capable of supporting the whole weight of the body. There are no cheek-pouches and no callosities, and the tympanic bullæ have no bony tubes leading into them. The thumb is but partially, or not at all, opposable and in some genera is absent.

The New World monkeys are, in general, smaller and lighter than those of the eastern hemisphere; there are no very large ones and they are all arboreal and are confined to the forested parts of the Neotropical region, except the West Indies, which have none. The marmosets (Hapalidæ), the first of the two families into which the Platyrrhina are divided, are little creatures, no longer than squirrels, with long, non-prehensile tails. They are characterized by the dental formula: _i_ 2/2, _c_ 1/1, _p_ 3/3, _m_ 2/2, × 2 = 32, and are the only Primates which have no third molar above or below. The thumb is not opposable, though quite long, and the hallux, or great toe, is very small; they are thus deficient in grasping power. Instead of the flat nails common to all the other Anthropoidea, they have long, sharp claws. All other South American monkeys are included in the family Cebidæ which, in turn, is divided into four subfamilies. It is not necessary to consider these or do more than cite a few illustrative examples.

[Illustration: FIG. 286.—Common Marmoset (_Hapale_).—By permission of W. L. Berridge, London.]

[Illustration: FIG. 287.—Sapajou (_Cebus_).—By permission of the New York Zoölogical Society.]

Some twenty species of the genus _Cebus_ are distributed from Central America to Paraguay; they have long, prehensile tails completely covered with hair, and well-developed thumbs. The monkeys of this genus are familiar to every one, as they are largely used by organ-grinders. The spider-monkeys (_Ateles_) are so called because of the great length and slenderness of their limbs; the tail is very long and perfectly prehensile, naked on the lower side near the end, which improves its grasping power. The hand has lost the thumb, but is used very effectively as a hook. The species, ten or more in number, have a wider range than those of _Cebus_ and extend from Uruguay to Mexico.

The howling monkeys (_Alouatta_, more commonly, but improperly, called _Mycetes_) are gifted with most unusual vocal powers. Mr. Bates says of them: “Morning and evening the howling monkeys make a most fearful and harrowing roar.” “The brief evening chorus of animals then began, the chief performers being the howling monkeys, whose frightful unearthly roar deepened the feeling of solitude which crept on as darkness closed around us.”[14] The tremendous volume of sound which these small creatures are able to produce is due to a resonating apparatus, formed by the great inflation of one of the hyoid bones (see p. 67), normally the bony support of the tongue. The tail is long and prehensile, with the end naked beneath; the thumb is well developed.

The sakis (_Pithecia_) have long and non-prehensile tail and complete thumb. The species of this genus have a remarkable kind of distribution, which is rare among mammals, though not infrequent for insects and birds. Each species is limited to a definite area of forest along the Amazon and its tributaries, which it occupies to the exclusion of the others. The uakaris (_Cacajao_) are distinguished by the tail, which is much shorter than in any other of the Cebidæ.

Finally, may be mentioned the nocturnal douroucoulis (_Nyctipithecus_), which have long, non-prehensile tail and well-developed thumb. Mr. Bates describes them thus: “A third interesting genus of monkeys, found near Ega, are the Nyctipitheci, or night apes, called Ei-á by the Indians.... They sleep all day long in hollow trees and come forth to prey on insects and eat fruits only at night. They are of small size, the body being about a foot long and the tail fourteen inches, and are thickly clothed with soft gray and brown fur, ... and the eyes are large and yellowish in colour, imparting the staring expression of nocturnal animals of prey.”[15]

The Brazilian caverns have preserved the remains of many Pleistocene monkeys belonging to existing South American genera, and even several modern species are represented, while others are extinct. There is also one extinct genus (_†Eriodes_), a larger animal than any of the existing Neotropical monkeys. The Pampean deposits of Argentina, on the other hand, have yielded no remains of Primates, nor is this surprising, for the Pampas would seem to have been open plains in the Pleistocene, as they are to-day. Between the Pleistocene and the Santa Cruz Miocene there is a long gap in the history. It is true that some bones have been found in the Pliocene of Monte Hermoso which have been referred to the Primates, but they are too few and imperfect to be of any real assistance in the inquiry.

In the Santa Cruz beds fossil monkeys are very rare, but that they were present in Patagonia at all, is strong evidence that the climate was then far milder than it is at present. These were essentially members of the modern family Cebidæ. The best-known genus, _†Homunculus_, retained a few primitive characters, which the existing genera have lost. For example, the premolars were relatively smaller and of simpler form and the humerus had the epicondylar foramen, though the femur no longer had the third trochanter. The radius was very modern in form and evidently could rotate freely upon the humerus.

No monkeys have been found in the Deseado formation, though too much stress should not be laid upon this fact, because of the general scarcity of small animals in those beds. But the same is true of the still more ancient stages; despite an abundant and varied fauna of small mammals, they have yielded no Primates, nor anything which could be seriously regarded as ancestral to them. The facts are essentially the same as we have found them to be with reference to the South American rodents and insectivores. All three of these orders appeared suddenly and unheralded in the Deseado (Rodentia) or Santa Cruz (Insectivora, Primates), and all of them were allied to African or European rather than to North American types. If we may assume the existence of a land-connection with Africa to account for the remarkable distribution of the hystricomorph rodents, the same connection will equally well explain the introduction of the Primates into South America.

Concerning the relations of the Old and New World monkeys, Mr. Beddard remarks: “Not only are these two groups of the Primates absolutely distinct at the present day, but they have been, so far as we know, for a very long time, since no fossil remains of Monkeys at all intermediate have been so far discovered. This has led to the suggestion that the Monkeys are what is termed diphyletic, _i.e._, that they have originated from two different stocks of ancestors. It is hard, however, to understand on this view the very great similarities which underlie the divergences that have just been mentioned. But, on the other hand, it is equally hard to understand how it is that, having been separated from each other for so long a period, they have not diverged further in structure than they have.”[16]

The fossil monkeys of the Santa Cruz beds show that, as a matter of fact, the South American Primates have undergone little change in the essentials of structure since that remote period, and thus is removed this objection to the conclusion that the Platyrrhina and Catarrhina were derived from a common ancestry. In a certain sense also, the discovery of _†Parapithecus_ in Egypt has diminished the gap between these two sections of the Anthropoidea. The evidence, though by no means conclusive, is distinctly in favour of the derivation of the South American monkeys from Old World ancestors. The Catarrhina have developed and advanced from the point of divergence far more than have the South American forms, which have changed relatively little since their invasion of the Neotropical region. So far as has been ascertained, South America never had any of the lemurs.

MAN IN THE WESTERN HEMISPHERE

Though to most people this is undoubtedly the most interesting chapter of all the mammalian history, little space can be given to it here, for the reason that the subject belongs rather in the domain of Anthropology and Ethnology than in that of Palæontology. There can be no question that Man originated in the eastern hemisphere and at a very remote period; abundant remains of his handiwork and of himself have been found in Europe as far back as the early Pleistocene, and recent discoveries in England have increased the already known length of the human habitation of Europe. So primitive and ape-like were some of these ancient men that they have been named as species (_Homo †neanderthalensis_ and _H. †heidelbergensis_) distinct from the existing _H. sapiens_. Recently discovered and very ancient remains in England have even been referred to a separate genus, _†Eoanthropus_.

As has been repeatedly pointed out in the preceding chapters, America received numerous successive waves of mammalian immigrants during the Pleistocene epoch, at a time when there was a broad land-connection between North America and Asia, where now is Bering Strait; and to this late connection is due the fact that the Boreal zone of North America (see p. 150) is zoölogically a part of the Old World and forms a division of the Holarctic region. Now, there is no known reason why Man, whose powers of dispersal are so superior to those of any other mammal, should not have accompanied these migrations, and it is entirely possible that he actually did so, but the fact has not been demonstrated. It is true that discoveries of Pleistocene Man have been frequently reported from both North and South America, but these have not stood the test of critical examination, though such examination has by no means disproved the presence of Pleistocene Man in America.

Dr. A. Hrdlička has recently concluded a series of exhaustive studies of the bones of early Man in both North and South America and of the localities where these bones were found. For both continents he has reached a negative result. As to North America he says: “Thus far on this continent no human bones of undisputed geologic antiquity are known.”[17] For South America the result is the same. “A conscientious, unbiased study of all the available facts has shown that the whole structure erected in support of the theory of geologically ancient man on that continent rests on very imperfect and incorrectly interpreted data and in many instances on false premises, and as a consequence of these weaknesses must completely collapse when subjected to searching criticism.” “The conclusions of the writers with regard to the evidence thus far furnished are that it fails to establish the claim that in South America there have been brought forth thus far tangible traces of either geologically ancient man himself or any precursor of the human race.

“This should not be taken as a categorical denial of the existence of early man in South America, however improbable such a presence may now appear.”[18]

On the other hand, the coexistence in North America of Man with several extinct species of mammals has been made extremely probable, if not certain. One of the most striking and best authenticated cases of this was the discovery by Professor Williston in western Kansas of a flint arrowhead beneath and in contact with the skeleton of the extinct _Bison †occidentalis_. Professor Russell found in lake deposits of Nevada an obsidian spear-head in association with the bones of an elephant or †mastodon, and other such instances have been reported. In these cases the doubt is as to the geological antiquity of the “finds,” for the implements are of the type made by the pre-Columbian Indians.

In brief, there is no convincing evidence that either North or South America was ever inhabited in prehistoric times by races of men different from those first encountered by the European discoverers.