A history of land mammals in the western hemisphere

by William Berryman Scott

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.