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.
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.