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.