continent of Miocene times exhibited in its fauna a combination
of all the main features which now characterise the Palæarctic,
Oriental, and Ethiopian regions; while tropical Africa, and such
other tropical lands as were then, like the peninsula of India,
detached and isolated from the continent, possessed a much more
limited fauna, consisting for the most part of animals of a lower
type, and which were more characteristic of Eocene or Secondary
times. Many of these have no doubt become extinct, but they are
probably represented by the remarkable and isolated lemurs of West
Africa and Southern Asia, by the peculiar Insectivora of South
Africa and Malaya, and by the Edentata of Africa and India. These
are all low and ancient types, which were represented in Europe
in the Eocene and early Miocene periods, at a time when the more
highly specialised horses, giraffes, antelopes, deer, buffaloes,
hippopotami, elephants, and anthropoid apes had not come into
existence. And if these large herbivorous animals were all wanting
in tropical Africa in Miocene times, we may be quite sure that the
large felines and other carnivora which prey upon them were absent
also. Lions, leopards, and hyænas can only exist where antelopes,
deer, or some similar creatures abound; while smaller forms allied
to the weasels and civets would be adapted to a country where small
rodents or defenceless Edentata were the chief vegetable-feeding
mammalia.
If this view is correct (and it is supported by a considerable amount
of evidence which it is not possible here to adduce), all the great
mammalia which now seem so specially characteristic of Africa--the
lions, leopards, and hyænas,--the zebras, giraffes, buffaloes,
and antelopes,--the elephants, rhinoceroses, and hippopotami,--and
perhaps even the numerous monkeys, baboons, and anthropoid apes,--are
every one of them comparatively recent immigrants, who took
possession of the country as soon as an elevation of the old Eocene
and Miocene sea-bed afforded a passage from the southern borders of
the Palæarctic region. This event probably occurred about the middle
of the Miocene period, and it must have effected a vast change in
the fauna of Africa. A number of the smaller and more defenceless
of the ancient inhabitants must have been soon exterminated, as
surely as our introduced pigs, dogs, and goats, exterminate so many
of the inhabitants of oceanic islands; while the new-comers finding
a country of immense extent, with a tropical climate, and not too
much encumbered with forest vegetation, spread rapidly over it, and
thenceforth, greatly multiplying, became more or less modified in
accordance with the new conditions. We shall find that this theory
not only accounts for the chief specialities, but also explains
many of the remarkable deficiencies of the Ethiopian fauna. Thus,
bears and deer are absent, because they are comparatively late
developments, and were either unknown or rare in Europe till late
Miocene or Pliocene times; while, on the other hand, the immense area
of open tropical country in Africa has favoured the preservation
of numerous types of large mammalia which have perished in the
deteriorated climate and diminished area of Europe.
Our knowledge of the geology of Africa is not sufficiently detailed
to enable us to determine its earlier history with any approach
to accuracy. It is clear, however, that Madagascar was once united
with the southern portion of the Continent, but it is no less clear
that its separation took place before the great irruption of large
animals just described; for all these are wanting, while lemurs,
insectivora, and civets abound,--the same low types which were once
the only inhabitants of the mainland. It is worthy of note, that
south temperate Africa still exhibits a remarkable assemblage of
peculiar forms of mammalia, birds, and insects,--the two former
groups mostly of a low grade of organisation; and these, taken in
connection with the wonderfully rich and highly specialised flora
of the Cape of Good Hope, point to the former existence of an
extensive south-temperate land in which so many peculiar types could
have been developed. Whether this land was separated or not from
Equatorial Africa, or formed with it one great southern continent,
there is no sufficient evidence to determine.
Turning now to tropical Asia, we find a somewhat analogous series of
events, but on a smaller scale and with less strongly-marked results.
At the time when tropical and South Africa were so completely cut
off from the great northern continent, the peninsula of India with
Ceylon was also isolated; and it seems probable that their union
with the continent took place at a somewhat later period. The
ancient fauna of this south-Asiatic island may be represented by the
slow Loris a peculiar type of lemurs, some peculiar rats (Muridæ),
and perhaps by the Edentate scaly ant-eater; by its Uropeltidæ a
peculiar family of snakes, and by many peculiar genera of snakes
and lizards, and a few peculiar amphibia. On the other hand, we
must look upon the monkeys, the large carnivora, the deer, the
antelopes, the wild pigs, and the elephants, as having overrun the
country from the north; and their entrance must, no doubt, have
led to the extermination of many of the lower types.
But there is another remarkable series of changes which have
undoubtedly taken place in Eastern Asia in Tertiary times. There
is such a close affinity between the animals of the Sunda Islands
and those of the Malay Peninsula and Siam; and between those of
Japan and of Northern Asia, that there can be little doubt that
these islands once formed a southern and eastern extension of the
Asiatic continent. The Philippines and Celebes perhaps also formed
a part of this continent; but if so, the peculiarity and poverty
of their mammalian fauna shows that they must have been separated
at a much earlier period.[68] The other islands probably remained
united to the continent till the Pliocene period. The result is seen
in the similarity of the flora of Japan to that which prevailed in
Europe in Miocene times; while in the larger Malay Islands we find,
along with a rich flora developed under long-continued equatorial
conditions of uniform heat and moisture, a remnant of the fauna
which accompanied it, of which the Malay tapir, the anthropoid apes,
the tupaias, the galeopitheci or flying lemurs, and the sun-bears,
may be representatives.
[68] For a full account of the evidence and conclusions as to these
islands see the author’s _Geographical Distribution of Animals_,
vol. i. pp. 345, 359, 426, 436.
There is another very curious set of relations worthy of our notice,
because they imply some former communication between the Malay
Islands, on the one hand, and South India with Ceylon, on the other.
We find, for example, such typical Malay forms as the Tupaia, some
Malay genera of cuckoos and Timaliidæ, some Malayan snakes and
amphibia. The remarkable genus Hestia among butterflies, and no less
than seven genera of beetles of purely Malay type,[69] all occurring
either in Ceylon only or in the adjacent parts of the Peninsula,
but in no other part of India. These cases are so numerous and so
important, that they compel us to assume some special geographical
change to account for them. But directly between Ceylon and Malaya
there intervenes an ocean-depth of more than 15,000 feet; and
besides the improbability of so great a subsidence, of which we
have no direct evidence, a land communication of this kind would
almost certainly have left more general proofs of its existence
in the faunas of the two countries. But, when in Miocene times a
subtropical climate extended into Central Europe, it seems probable
that the equatorial belt of vegetation accompanied by its peculiar
fauna, would have been wider than at present extending perhaps as
far as Burma. If then the shallow northern part of the Bay of Bengal
had been temporarily elevated during the late Miocene or Pliocene
epochs, a few Malayan types may have migrated to the Peninsula of
India; and have been preserved only in Ceylon and the Nilgherries,
where the climate still retains somewhat of its equatorial character
and the struggle for existence is somewhat less severe than in the
northern part of the region, which is so much more productive in
varied forms of life.
[69] For details see _Geographical Distribution of Animals_, vol.
i. p. 327.
There are also indications hardly less clear, of some communication
between India and Malaya on the one hand, and Madagascar on the
other; but as these indications depend chiefly on resemblances in
the birds and insects, they do not imply that any land connection
has occurred. If, as seems probable, the Laccadive and Maldive
Islands are the remains of a large island or indicate a western
extension of India, while the Seychelles, with the shallow banks
to the south-east and the Chagos group are the remains of other
extensive lands in the Indian Ocean, we should have a sufficient
approximation of these outlying portions of the two continents to
allow a certain amount of interchange of such winged groups as birds
and insects, while preventing any intermixture of the mammalia.
The presence of some African types (and even some African species)
of mammals in Hindostan appears to be due to more recent changes,
and may perhaps be explained by a temporary elevation of the
comparatively shallow borders of the Arabian Sea, admitting of a
land passage from North-East Africa to Western India.
There remains to be considered the supposed indications of a very
ancient communication between Africa, Madagascar, Ceylon, Malaya,
and Celebes, furnished by the occurrence over this extensive area
of isolated forms of the Lemur tribe. The anomalous range of this
group of animals has been thought to require for its explanation
the existence of an ancient southern continent which has been
called Lemuria, but a consideration of all the facts does not seem
to warrant such a theory. Had such a continent ever existed we are
sure that it must have disappeared long before the Miocene period,
or it would assuredly have left more numerous and widespread
indications of the former connections of these distant lands than
actually exist. And when we go back to the Eocene period we are met
by the interesting discovery of an undoubtedly Lemurine animal in
France, and what are supposed to be allied forms in North America.
This proof of the great antiquity and wide range of lemurs is
quite in accordance with their low grade of development; while the
extreme isolation and specialization of many of the existing types
(of which the Aye-aye of Madagascar is a wonderful example), and
their scattered distribution over a wide tropical area, all suggest
the idea that these are but the remnants of a once extensive and
widely distributed group of animals, which, in competition with
higher forms, have preserved themselves either by their solitary
and nocturnal habits, or by restriction to ancient islands, like
Madagascar, where the struggle for existence has been less severe.
Lemuria, therefore, may be discarded as one of those temporary
hypotheses which are useful for drawing attention to a group of
anomalous facts, but which fuller knowledge shows to be unnecessary.
_Regions of the New World._--We will now pass across the Atlantic
to the Western Hemisphere, and consider first the Nearctic region,
or temperate North America, whose present and past zoological
relations with the rest of the world are of exceeding interest.
If we omit such animals as the musk-sheep (Ovibos), which is
purely Arctic, and the peccaries (Dicotyles), which are hardly
less distinctly tropical, the land-mammalia of North America
are not very numerous; and they can be for the most part divided
into two groups, the one allied to the Palæarctic, and the other
to the Neotropical fauna. The bears, the wolves, the cats, the
bison, sheep and antelope, the hares, the marmots, and the pikas,
resemble Palæarctic forms; while the racoons, skunks, opossum, and
vesper-mice are now more peculiarly Neotropical. There are also
many genera which are altogether peculiar and characteristic of the
region, as the prong-horn antelope (Antilocapra), the jumping-mouse
(Jaculus), five genera of pouched rats (Saccomyidæ), the prairie
dogs (Cynomys), the tree porcupines (Erethizon), and some others.
Birds present the same mixture of the two types; but the wild turkeys
(Meleagris), the passenger pigeon (Ectopistes), the crested quails
(Lophortyx, &c.), the ruffed grouse (Cupidonia), and some other
groups of less importance, are peculiar; while the family of the
wood warblers (Mniotiltidæ) is so largely developed that it may
claim to be more characteristic of North than of South America.
Reptiles and Amphibia present a number of peculiar types; while no
less than five peculiar families of fresh-water fishes would alone
serve to mark out this as distinct from every other part of the
world.
Considering the evident affinity between the Nearctic and Palæarctic
regions, there are here some curious deficiencies of groups which
are common and widely spread in the latter. Thus hedgehogs, wild
horses and asses, swine, true oxen, goats, dormice, and true mice are
absent; while sheep and antelopes are only represented by solitary
species in the Rocky Mountains. Among birds, too, we have such
striking deficiencies as the extensive families of flycatchers,
starlings, and pheasants.
Turning now to the Neotropical region, comprising all South America
and the tropical parts of the northern continent, we find that the
Old World types have still further diminished, while a number of new
and altogether peculiar forms have taken their place. Insectivora
have wholly disappeared with the exception of one anomalous form
in the greater Antilles; bears are represented by one Chilian
species; swine are replaced by peccaries; the great Bovine family
are entirely unknown; the camel tribe are confined to the Southern
Andes and the south-temperate plains; deer are not numerous; and
all the varied Ungulata of the Old World are represented only by
a few species of tapirs. These great gaps are, however, to some
extent filled up by a variety of interesting and peculiar types. Two
families of monkeys (Cebidæ and Hapalidæ) differ in many points of
structure from all the Quadrumana of the eastern hemisphere. There
is a peculiar family of bats--the vampyres; many peculiar weasels
and Procyonidæ; a host of peculiar rodents, comprising five distinct
families, among which are the largest living forms of the order; and
a great number of Edentata, comprising the families of the sloths,
armadillos, and ant-eaters; and lastly, a considerable number of
the marsupial family of opossums. As compared with the Old World,
we find here a great abundance and variety of the lower types, with
a corresponding scarcity of such higher forms as characterise the
tropics of Africa and Asia.
In birds we meet with corresponding phenomena. The most abundant
and characteristic families of the Old World tropics are replaced
here by a series of families of a lower grade of organisation, among
which are such remarkable groups as the chatterers (Cotingidæ), the
manakins (Pipridæ), the ant-thrushes (Formicariidæ), the toucans
(Rhamphastidæ), the motmots (Momotidæ), and the humming-birds
(Trochilidæ), the last perhaps the most remarkable and beautiful
of all developments of the bird-type. Parrots are numerous, but
these, too, are mostly of peculiar families; while pheasants and
grouse are replaced by curassows and tinamous, and there are an
unusual number of remarkable and isolated forms of waders.
Reptiles, amphibia, fresh-water fishes, insects, and land-shells,
are all equally peculiar and abundant; so that South America
presents, on the whole, an assemblage of curious and beautiful
natural objects, unsurpassed--perhaps even unequalled--in any other
part of the globe.
_Past History of the American Continents._--We will now proceed
to examine what is known of the past history of the two American
continents, and endeavour to determine what have been their former
relations to each other and to the Old World, and how their existing
zoological and geographical features have been brought about. And
first let us see what knowledge we possess of the past relations
of North America with the Eastern continents.
If we go back to that recent period termed the
Post-Pliocene--corresponding nearly to the Post-Glacial period and
to that of prehistoric man in Europe--we find at once a nearer
approximation than now exists between the Nearctic and Palæarctic
faunas. North America then possessed several large cats, six distinct
species of the horse family, a camel, two bisons, and four species
of elephants and mastodons. A little earlier, in the Pliocene
period (although fossil remains of this age are scanty), we have
in addition the genus Rhinoceros, several distinct camels, some new
forms of ruminants and an Old-World form of porcupine. Further
back, in the Miocene period, we find a Lemuroid animal, numerous
insectivora, a host of carnivora, chiefly feline and canine, a
variety of equine and tapirine forms, rhinoceroses, camels, deer,
and an extensive extinct family--the Oreodontidæ--allied to deer,
camels, and swine. There are, however, no elephants. In the still
earlier Eocene period most of the animals were peculiar, and unlike
anything now living, but some were identical with European types
of the same age, as Lophotherium and the family Anchitheridæ.
These facts compel us to believe that at distinct epochs during the
Tertiary period the interchange of large mammalia between North
America and the Old World has been far more easy than it is now. In
the Post-Pliocene period, for example, the horses, elephants, and
camels of North America and Europe were so closely allied that their
common ancestors must have passed from one continent to the other,
just as we feel assured that the common ancestors of the American
and European bison, elk, and beaver, must have so migrated. We have
further evidence in the curious fact that certain groups appear to
come into existence in the one continent much later than in the
other. Thus cats, deer, mastodons, true horses, porcupines, and
beavers, existed in Europe long before they appeared in America; and
as the theory of evolution does not admit the independent development
of the same group in two disconnected regions to be possible, we
are forced to conclude that these animals have migrated from one
continent to the other. Camels, and perhaps ancestral horses, on
the other hand, were more abundant and more ancient in America,
and may have migrated thence into Northern Asia.
There are two probable routes for such migrations. From Norway
to Greenland by way of Iceland and across Baffin Bay to Arctic
America, there is everywhere a comparatively shallow sea, and it is
not improbable that during the Miocene period, or subsequently, a
land communication may have existed here. On the other side of the
continent, at Behring Straits, the probability is greater. For here
we have a considerable extent of far shallower sea, which a very
slight elevation would convert into a broad isthmus connecting North
America and North-East Asia. It is true that elephants, horses, deer,
and camels would, under existing climatal conditions, hardly range
as far north as Greenland and Alaska; but we must remember that
most mysterious yet indisputable fact of the luxuriant vegetation,
including even magnolias and other large-leaved evergreens, which
flourished in these latitudes during the Miocene period; so that
we have all the conditions of favourable climate and abundant
food, which would render such interchange of the animals of the
two continents not only possible, but inevitable, whenever a land
communication was effected; and there is reason to believe that
this favourable condition of things continued in a diminished degree
during a portion of the succeeding Pliocene period.
We must not forget, however, that the faunas of the two continents
were always to a great extent distinct and contrasted--such
important Old-World groups as the civets, hyænas, giraffes, and
hippopotami, never passing to America, while the extinct Oreodontidæ,
Brontotheridæ, and many others are equally unknown in the Old World.
This renders it probable that the communication even in the north
was never of long continuance; while it wholly negatives the theory
of an Atlantis bridging over the Atlantic Ocean in the Temperate
Zone at any time during the whole Tertiary period.
But the past history of the North American fauna is complicated by
another set of migrations from South America, which, like those
from the Old World, appear to have occurred at distant intervals,
and to have continued for limited periods. In the Post-Pliocene
epoch, along with elephants and horses from Europe or Asia, we
find a host of huge sloths and other Edentata, as well as llamas,
capybaras, tapirs, and peccaries, all characteristic of South
America. Some of these were identical with living species, while
others are closely allied to those found fossil in Brazilian caves
and other deposits of about the same age, while nothing like them
inhabited the Old World at the same period. We are therefore quite
sure that they came from some part of the Neotropical region; but
the singular fact is, that in the preceding Pliocene epoch none of
them are found in North America. We conclude, therefore, that their
migration took place at the end of the Pliocene or beginning of the
Post-Pliocene epoch, owing to some specially favourable conditions,
but that they rapidly disappeared, having left no survivors. We
must, however, study the past history of South America in order to
ascertain how far it has been isolated from or connected with the
northern continent.
Abundant remains of the Post-Pliocene epoch from Brazilian caves
show us that the fauna of South America which immediately preceded
that now existing had the same general characteristics, but was
much richer in large mammalia and probably in many other forms of
life. Edentata formed the most prominent feature; but instead of
the existing sloths, armadillos, and ant-eaters, there were an
immense variety of these animals, some of living genera, others
altogether different, and many of them of enormous size. There were
armadillos as large as the rhinoceros, while the megatherium and
several other genera of extinct sloths were of elephantine bulk. The
peculiar families of South American rodents--cavies, spiny-rats,
and chinchillas--were represented by other species and genera, some
of large size; and the same may be said of the monkeys, bats, and
carnivora. Among Ungulata, however, we find, in addition to the
living tapirs, llamas, peccaries, and deer, several species of horse
and antelope, as well as a mastodon, all three forms due probably
to recent immigration from the northern continent.
Further south, in Bolivia, the Pampas, and Patagonia, we also find
abundant fossil remains, probably a little older than the cave
fauna of Brazil, and usually referred to the newer part of the
Pliocene period. The same families of rodents and Edentata are
here abundant, many of the genera being the same but several new
ones also appearing. There are also horses, peccaries, a mastodon,
llamas, and deer; but besides these there are a number of altogether
peculiar forms, such as the Macrauchenia, allied to the Tapir
and Palæotherium; the Homalodontotherium, allied to the Miocene
Hyracodon of North America; and the Toxodontidæ, a group of very
large animals having affinities to Ungulates, rodents, Edentata,
and Sirenia, and therefore probably the representative of a very
ancient type.