THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS
To every one who has paid the slightest attention to the subject, it is a
familiar fact that different parts of the earth have different animals;
school-children learn from their geographies that kangaroos are found
in Australia, the Hippopotamus in Africa, the Tiger in southern Asia,
armadillos and llamas in South America. These examples are all taken from
distant lands, yet the zoölogical difference between two given land-areas
is by no means proportional to the distance between them. An Englishman
landing in Japan finds himself surrounded by animals and plants very
like and often identical with those which he left at home, while the
narrow Strait of Lombok, east of Java, separates two profoundly different
regions. In crossing Mexico from east to west, the traveller meets very
different animals in closely adjacent areas; and, at first sight, the
arrangement of animals appears to be so capricious as to admit of no
formulation in general laws.
In pre-Darwinian times, when it was the almost universal belief that
each species had been separately created and was exactly fitted to the
region which it inhabits, no explanation of the geographical arrangement
of animals was possible, but the acceptance of the theory of evolution
demanded that such an explanation should be found. A failure to devise
any rational and satisfactory account of the geography of animal life
would be a fatal weakness in the evolutionary theory, hence the facts of
distribution were subjected to a renewed and searching analysis as one
of the best means of critically testing the new doctrine. Not that the
subject had received no attention before the publication of Darwin’s
book; on the contrary, it had attracted much interest as a study of
facts, and this study was one of the principal avenues by which Darwin
approached his great generalization. In his autobiographical fragment
he tells us: “I had been deeply impressed by discovering in the Pampean
formation great fossil animals covered with armour like that on the
existing armadillos; secondly, by the manner in which closely allied
animals replace one another in proceeding southward over the Continent;
and third, by the South American character of most of the productions of
the Galapagos archipelago and more especially by the manner in which they
differ slightly in each island of the group.”
Obviously, before attempting to explain the facts of the geographical
distribution of mammals, we must first ascertain what those facts are.
The following brief sketch of the terms used in describing geographical
arrangement is summarized from Mr. Wallace’s “Island Life.”
Though with fluctuating boundaries and subject to slow secular changes, a
mammalian species is limited to a fairly definite area, which may be of
immense or very restricted extent, and throughout which it may be found
in greater or less abundance. Many species, however, are not distributed
continuously over the areas which they inhabit, but occur only in
suitable _stations_ adapted to their habits and mode of life. Thus, some
will be found only where there are trees, others in the neighbourhood of
water, others only on open plains, etc. A _specific area_ is then the
whole extent of country within which the species may be found, while the
_stations_ are the limited districts contained in the area which are
exactly suited to the habits of the species in question; these stations
may be hundreds of miles apart, as in the case of mountain-tops, or they
may be close together. A marsh-living species, for example, will occur
in all the marshes throughout its area, whether these be many or few,
near together or widely scattered; for such a species marshes are its
stations.
_Generic areas_ differ in character according as the genus is large,
that is, comprising many species, or small and having but few species,
or, it may be, a single one. The species, as a rule, occupy each its own
area, and the areas may be entirely distinct, or they may be contiguous
and more or less extensively overlapping, though it seldom happens that
two or more species of the same genus inhabit exactly the same area.
Often some physical feature, such as a range of high mountains, a great
river, the edge of a forest, plain or desert, exactly defines the limits
of species of the same genus. The Amazon, for example, acts as such a
boundary to many species. It was to this change of related species from
one area to another that Darwin referred in the passage quoted above,
saying that he had been deeply impressed “by the manner in which closely
allied animals replace one another in proceeding southward over the
Continent [_i.e._ South America].” On the other hand, the overlapping of
areas may be very extensive, and one species of great range may cover the
whole area of another and much more besides.
A remarkable example of the widely separated areas of species belonging
to the same genus is that of the tapirs. Of this genus there are two
or three species in Central and South America and one inhabiting the
Malay Peninsula and Borneo, almost as wide a separation as the size of
the earth permits. Discontinuous distribution of this character can be
explained in terms of the evolutionary theory only in one of two ways.
Either (1) the American and Asiatic species developed independently of
one another from different ancestors, or (2) the regions intervening
between these widely separated areas once formed a continuous land,
occupied by species of the genus which have become extinct. From all that
we know concerning the operation of the evolutionary process, the first
alternative may be set aside as altogether improbable, and, even had we
no information concerning the history of the tapirs and their former
distribution, the second explanation would be chosen as incomparably the
more likely. As a matter of fact, we have definite knowledge that tapirs
once ranged all over Europe and North America and doubtless over northern
Asia, as well, and, further, that North America was joined to Asia by a
land occupying the place of the shallow Bering Sea, at a time when the
tapirs were able to take advantage of this means of passing from one
continent to the other. Such appears to be the invariable explanation of
discontinuous distribution, though we may not always be able to give so
clear a proof of it.
The genera of a family are distributed in much the same fashion as the
species of a genus, but, as a rule, much more widely. While no genus of
terrestrial mammals is cosmopolitan (_i.e._ universally distributed),
at least as genera are defined and limited by most modern systematists,
certain families are represented in every continent. If the extremely
peculiar and isolated Australian continent be excepted, the number
of such cosmopolitan families is considerable and wide separation
between the genera is frequent. Of the camel family, for instance, one
genus, that of the true Camel (_Camelus_), is confined to the northern
hemisphere and the Old World, the other (_Lama_), comprising the Llama,
Guanaco, etc., is found only in the southern hemisphere and the New
World. Less extreme instances of the discontinuous distribution of a
family are common enough.
The principles of distribution are the same when applied to families and
orders. Most of the mammalian orders are very widely distributed and many
are cosmopolitan, except for Australia, though some are confined to one
or two continents. The monotremes are limited to Australia and Tasmania,
the marsupials to Australia and the Americas, the edentates to the
latter, the elephants and hyracoids to Africa and Asia. Carnivores and
rodents, on the contrary, are found in every continent, even Australia.
We have next to inquire what is the nature of the obstacles or barriers
that prevent the indefinite spread of terrestrial mammals, so that the
mammalian fauna of the whole earth, and even of a single continent,
is not uniform, but highly variegated. The rate of multiplication of
animals is so rapid that, under normal conditions, the animal population
is always pressing hard upon the means of subsistence and every species
that is increasing in numbers must constantly extend its range in search
of food. Every species would increase indefinitely, if there were no
countervailing checks. Were all the young to survive and breed in their
turn, “even large and slow-breeding mammals, which only have one at a
birth, but continue to breed from eight to ten successive years, may
increase from a single pair to 10,000,000 in forty years” (Wallace).
Evidently, a species must spread from its place of origin until stopped
by insuperable obstacles, the most obvious of which are wide seas. A few
land mammals are not only excellent swimmers, but will cross straits
without hesitation, as the Guanaco has been seen to swim the Straits
of Magellan; for the great majority, however, a very few miles of sea
form an impassable barrier. As was shown above, a broad or deep river is
sufficient to limit many species, as the Santa Cruz River in Patagonia
marks the southern boundary of the armadillos.
Important geographical changes, such as the joining of lands that before
were separate, or the dividing of continuous lands by transgressions
and incursions of the sea, must necessarily have a profound effect upon
the distribution of land mammals. Separated land-areas, however similar
may have been their faunas at the time of separation, will, through the
operation of the divergent evolutionary process, grow more unlike in
proportion to the length of time that the separation continues. Regions
which have been severed within a short time (in the geological sense of a
short time) are zoölogically very similar or even identical, while those
that have long been isolated are correspondingly peculiar. Attention has
already been called, in another connection, to the contrasted cases of
such great continental islands as Great Britain, Java, Sumatra, etc.,
on the one hand, and Australia, on the other. The continental islands,
which have but lately been detached from the neighbouring main lands,
are hardly more peculiar zoölogically than equal areas of the adjoining
continents, while the long-continued isolation of Australia has made it
the most peculiar region of the earth. Climatic changes, which, as we
saw in Chapter I, have indubitably taken place many times, have also had
a great effect in shifting the distribution of mammals, which in its
present form is the outcome of a very long series of geographical and
climatic changes, on the one hand, and of adaptive changes in the animals
themselves, on the other.
Of almost equal importance as a barrier is climate and especially
temperature. Not that similar climates can produce similar forms in
separate areas. Regions of almost exactly similar climate in Australia,
Africa and South America have totally different faunas, but, _within
continuous land-areas_, the most effective of barriers is temperature.
This acts differently in the case of limiting the northward spread
of southern forms and the southward spread of northern species. Dr.
Merriam’s long study of this problem has led him to the conclusion
that southern species are bounded on the north by the temperature of
the breeding season, in which the total quantity of heat must reach a
certain minimum, while “animals and plants are restricted in southward
distribution by the mean temperature of a brief period covering the
hottest part of the year.” On the Pacific coast there is a remarkable
mingling in the same areas of species which, east of the high mountains,
are distributed in sharply separated zones. This is explained by the mild
and equable climate of the coastal belt, where the hottest season of the
year does not reach the limiting maximum for the northern species, while
the total quantity of heat in the breeding season is sufficient to enable
southern species to thrive and maintain themselves.
Dr. Merriam thus sums up the effects of climatic factors upon
distribution: “Humidity and other secondary causes determine the presence
or absence of particular species in particular localities within their
appropriate zones, but temperature pre-determines the possibilities of
distribution; it fixes the limits beyond which species cannot pass.”
“Concurrently with these changes in vegetation from the south northward
occur equally marked differences in the mammals, birds, reptiles,
and insects. Among mammals the tapirs, monkeys, armadillos, nasuas,
peccaries, and opossums of Central America and Mexico are replaced to the
northward by wood-rats, marmots, chipmunks, foxes, rabbits, short-tailed
field-mice of several genera, shrews, wild-cats, lynxes, short-tailed
porcupines, elk, moose, reindeer, sables, fishers, wolverines, lemmings,
musk-oxen, and polar bears.”
Dr. J. A. Allen has reached closely similar conclusions. “Of strictly
climatic influences, temperature is by far the most important, although
moisture plays an influential part. Where a low temperature prevails
life, both animal and vegetable, is represented by comparatively few
forms; under a high temperature it is characterized by great diversity
and luxuriance. Within the Arctic Circle the species of both animals
and plants are not only few, but they are widely distributed, being for
the most part everywhere the same. Under the tropics they are a hundred
fold more numerous and of comparatively restricted distribution.” “The
influence of temperature is perhaps most strikingly displayed in the
distribution of life upon the slopes of a high mountain, especially if
situated near the tropics. While its base may be clothed with palms
and luxuriant tropical vegetation, its summit may be snow-capped
and barren.... The animal life becomes likewise correspondingly
changed, tropical forms of mammals, birds, and insects of the lower
slopes gradually giving place to such as are characteristic of arctic
latitudes.” “The effect of humidity upon plant life is thus obvious,
but it is equally potent, though less evident, upon animal life. Many
animals ... are so fitted for a forest life, as regards both food and
shelter, that their very existence depends upon such surroundings....
Thus moisture alone may determine the character of life over extensive
regions.”
While climate is thus the most important of the barriers which determine
distribution in continuous land-areas, the absence of any particular
species from a given region is no proof that the climate is unsuitable
to that species. This is sufficiently shown by the manner in which
animals introduced into a new country often run wild and multiply to an
incredible extent, as the rabbits have done in Australia, the Mongoose in
Jamaica, horses on our western plains, horses and cattle on the Pampas of
Argentina, etc.
Topographical features, such as great mountain-ranges and plateaus,
also limit many species, not only by the difficulty of crossing them,
but also by the effect which they have upon temperature and moisture.
For this reason long ranges of mountains and table-lands may carry a
northern fauna very far to the south of its ordinary range, as do the
mountain-systems of North America in a very conspicuous manner. The
great Mexican plateau is zoölogically a part of North America, while the
low coastal lands as far as southeastern Texas have Central American
affinities.
A different kind of obstacle to the spread of a species into a new
area may be the pre-occupation of that area by another species. The
pre-occupier may be one that plays so similar a part in the economy of
nature as to leave no opportunity for the newcomer to establish itself.
On the other hand, the obstructing form may be an active enemy and of
a totally different character from the intruder, as in the case of the
Tse-tse Fly in parts of Africa. The bite of the fly is fatal to horses
and oxen, so that these mammals are unable to enter the fly-infested
regions. Many times in the course of the Tertiary period various mammals
reached North America from the south or from the Old World, which
were unable to gain a permanent foothold and speedily died out. At
this distance of time it is seldom, if ever, possible to explain why a
species which succeeded in reaching this continent could not maintain
itself, though the most probable assumption is that the forms already in
possession of the land were an insuperable obstacle to the intruders.
The rate of dispersal of a species into new areas may be fast or slow,
according as the conditions are more or less favourable. Newly introduced
insect-pests, like the Gypsy and the Brown-tailed Moths in New England,
often spread with portentous rapidity; and introduced mammals have
frequently taken possession of vast areas in a surprisingly short time.
One of the most remarkable of these cases is cited by Darwin. “In the
time of Sarmiento (1580) these Indians had bows and arrows, now long
since disused; they then also possessed some horses. This is a very
curious fact, showing the extraordinarily rapid multiplication of horses
in South America. The horse was first landed at Buenos Ayres in 1537
and the colony being then for a time deserted, the horse ran wild; in
1580, only forty-three years afterwards, we hear of them at the Strait
of Magellan!” (“Voyage of a Naturalist,” pp. 232-233.) In this example,
something must be allowed for human agency, but even so, it is very
surprising.
In the case of lands newly raised above the sea and connecting formerly
separated areas, it is necessary that they should first be taken
possession of by vegetation, before they can become passable by animals,
for the migration of mammals from continent to continent is an entirely
distinct phenomenon from the annual migration of birds. The latter,
though a fact familiar to every one, is an unexplained mystery, and it is
somewhat unfortunate that the same term should be used for the completely
different process of the spread of mammals into newly opened land. This
spread is purely unconscious and is due to the pressure of increasing
numbers upon the means of subsistence, each new generation ranging
farther and farther from the original home of the species and continuing
so to extend until some insuperable obstacle is encountered. When a
sea-barrier is removed by upheaval and the newly formed land rendered
habitable for mammals through the invasion of plants, the interrupted
process is resumed and an interchange of species between the areas thus
connected is brought about. The interchange is, however, always an
incomplete one, certain forms not being able so to extend their range,
because of climatic differences, pre-occupation or some such barrier.
It is customary to give a graphic expression to the facts of animal
distribution by dividing the land surface of the earth into districts
which are characterized by their faunas. It is not possible to construct
a geographical scheme which will be equally satisfactory for all classes
of animals, because the geological date of most rapid development and
diffusion was so different in the various classes. The geographical and
climatic conditions which favoured a particular geographical arrangement
of one class had been so completely altered that the class coming in
later could not attain a similar distribution. For this reason, land
mammals are chosen as affording the best criteria; their adaptability is
such that they are found all over the earth, their dispersal is primarily
dependent upon the arrangement and connections of the continental
land-masses, modified by the topographical and climatic conditions, and
they, with the birds, are the latest of the vertebrate classes to assume
a dominating importance. Their history is the most fully known and falls
within the best understood portion of the earth’s history, making it
possible to follow their migrations with a precision which is seldom
feasible for the other classes of animals, and thus to correlate the
successive physical and organic changes. A particularly great advantage
which mammals possess for this purpose is that the mutual relationships
of the various kinds are better understood than in the case of most
other groups of animals. It is true that we shall find a great many
unsolved problems, upon which the most divergent opinions are held, but
the main outlines of the scheme are quite generally agreed upon.
Many plans for the zoölogical division of the continental areas have been
proposed by various writers on the subject, some differing very radically
from others. It would be useless and tedious to review even the more
important of the many proposals and suggestions which have been made in
the last half-century; and we may, with advantage, adopt an eclectic
scheme which has been slowly reached by successive approximations to a
satisfactory arrangement.
Just as in political geography it is found necessary to recognize
divisions of different rank and scope, like nation, state, county,
township, the facts of zoölogical geography require divisions of
different orders of importance. Thus, in descending order, the terms
_realm_, _region_, _subregion_, _province_, etc. are commonly employed,
but unfortunately they are often used loosely and even interchangeably;
yet it is desirable to attach a more or less precise significance to each
and more terms are needed for an accurate expression of the many complex
facts.
The extreme zoölogical peculiarity of Australia is recognized by making
that continent and its adjoining islands one of the great primary
divisions, of which the other includes all the rest of the world; the
former is characterized by its almost exclusively marsupial fauna, while
the other continents are inhabited by the Monodelphia or placental
mammals. Aside from Australia, by far the most isolated and peculiar
region of the earth is South America, and this fact is expressed by
constituting it into a _realm_, or division of the second order, and to
this realm is given the name _Neogæa_. The remaining continents, North
America, Europe, Asia and Africa, make up the other realm, _Arctogæa_,
in which there is an unmistakable general likeness among the mammals.
The three continents of the Old World form a vast, connected land-mass,
and the final separation of North America from this great complex is an
event of geologically recent date. For reasons that will be made clear
in the course of the history, the junction of the two Americas has had
comparatively little effect upon the zoölogy of the northern continent,
except in its tropical portion. It is obvious from a glance at the
map, that the great zoölogical divisions are of very unequal size, but
the arrangement is made on the basis of degrees of difference in the
mammalian faunas. These degrees of difference are, in turn, an expression
of length of separation or of the difficulty of communication between
connected lands.
The following table gives the major divisions of the earth apart from
Australia:
I. NEOGÆIC REALM. _Neotropical Region._—South and Central America,
lowlands of Mexico, the West Indies.
II. ARCTOGÆIC REALM. { 1. _Malagasy Region._—Madagascar.
{ 2. _Ethiopian Region._—Africa south of the
{ Sahara Desert.
{ 3. _Oriental Region._—Southern peninsulas of
{ Asia, Malay Archipelago.
{ 4. _Holarctic Region._—N. Africa, Europe, Asia,
{ (except southern part), boreal N. America.
{ 5. _Sonoran Region._—Remainder of N. America
{ (except lowlands of Mexico).
North America, as is expressed by this scheme, is zoölogically composite;
the northern half, including nearly all of Canada, belongs to the vast
Holarctic Region, which also comprises Europe, Africa north of the
Sahara and Asia north of the Himalaya Mountains. The remainder of the
continent, exclusive of the Mexican coastal lowlands, is set off as the
Sonoran Region. Inasmuch as we have here to do with broadly continuous
land-areas, not demarcated by great physical features, and as the genera
and species of mammals differ greatly in regard to their ability to
withstand a wide range of climatic variations, it is not to be expected
that the boundaries between the regions which make up North America
should be very sharply drawn. It is not surprising, therefore, to find
a transition zone, extending all across the continent, in which the
Holarctic and Sonoran faunas mingle, or that Central America should,
in considerable measure, be transitional to South America, though
zoölogically a part of the latter.
[Illustration: FIG. 53.—Zoölogical Divisions of North America. (After
Merriam.)]
Dr. Merriam’s arrangement, which deals only with North America
without reference to the Old World, divides the land into a series of
transcontinental zones, which he calls the Arctic, Boreal, Upper and
Lower Sonoran and Tropical. These zones have very irregular and sinuous
boundaries, which follow lines of equal temperature (isothermal lines)
during the breeding season, May, June and July, the tortuous boundaries
being conditioned by topographical features, which deflect the isothermal
lines.
[Illustration: FIG. 54.—Polar Bear (_Thalarctus maritimus_).—By
permission of the N.Y. Zoölog. Soc.]
The Arctic zone is part of a circumpolar area, which is very much the
same in North America, Asia and Europe; and in any of these continents
the fauna differs much more from that of the contiguous zone to the south
than from the Arctic fauna of another continent. There are some local
differences, but the characteristic mammals of this Arctic zone are the
Polar Bear, Arctic Fox, Musk Ox, Barren-ground Caribou, Lemming, Arctic
Hare, and a marmot. Most, if not all, of these forms are of Old World
origin.
[Illustration: FIG. 55.—Musk Ox (_Ovibos wardi_) female; the males have
much larger horns.—By permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 56.—Arctic Fox (_Vulpes lagopus_) in winter dress.—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 57.—Arctic Fox in summer dress.—By permission of the
N.Y. Zoölog. Soc.]
The American portion of the great Holarctic region is called by Mr.
Lydekker, who uses Wallace’s term, the “Canadian subregion,” and by
Dr. Merriam the “Boreal region.” Not that there is any difference of
principle involved in this varying nomenclature, for Dr. Merriam says:
“It so happens that the Boreal element in America resembles that of
Eurasia so closely that in the judgment of many eminent authorities
the two constitute a single primary region—a view in which I heartily
concur.” The Canadian or Boreal subregion of the Holarctic is the great
belt of coniferous forest, which extends obliquely across North America
from Alaska to New England; its frontier with the Arctic zone is the
northern limit of trees and it is divided from the Transition zone
approximately by the line of latitude 45° N., though with a sinuous
course, and it is carried far to the south by the wooded heights of the
Appalachian, Rocky and Sierra Nevada Mountains, and along the Pacific
coast, the mixed character of which has already been explained; it
extends almost to San Francisco. The subregion is further divisible into
northern and southern belts, called the Hudsonian and Canadian faunas,
the limit between them approximately following the isothermal line of
57° F. The mammals of this subregion are largely of Old World origin,
many of them coming in with the great immigrations of the Pliocene and
Pleistocene epochs; but there are also native American elements and even
one genus of South American origin, the Short-tailed or Canada Porcupine
(_Erethizon_).
[Illustration: FIG. 58.—Canada Porcupine (_Erethizon dorsatus_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 59.—Woodchuck or Marmot (_Marmota monax_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 60.—Mink (_Lutreola vison_).—By permission of the
N.Y. Zoölog. Soc.]
In considering the mammals of this subregion, it should be remembered
that they are not uniformly distributed throughout even one subdivision,
but in a scattering way and in accordance with their habits and stations,
and also in accordance with a gradual change to the south, following the
changing temperature. The Muskrat will not be found far from water or the
Porcupine from woods. Especially characteristic of the Canadian subregion
are the Old World types of deer, none of which range farther south than
the Transition zone. The Wapiti, erroneously called the Elk (_Cervus
canadensis_), is very closely allied to the European Stag (_C. elaphus_)
and still more closely to the Stag of the Thian Shan in Central Asia (_C.
eustephanus_). So great is the resemblance, that some naturalists would
refer all three forms to a single species. The Moose (_Alce americanus_),
which should be called the Elk, is so near to the Scandinavian Elk (_A.
machlis_) that it is hardly distinguishable as a separate species, and
the Woodland Caribou (_Rangifer caribou_) is the American representative
of the Lapland Reindeer (_R. tarandus_). The so-called Rocky Mountain
Goat (_Oreamnos montanus_), a peculiar and aberrant form of the Chamois
subfamily of the Antelopes, is confined to the subregion. The Mountain
Sheep (_Ovis montana_, _O. dalli_) are represented by three or four
species, one of which extends into the Sonoran region, as does also the
Bison, wrongly called Buffalo (_Bison bison_), which is nearly allied to
the European _B. bonasus_. In Cæsar’s time the European Bison (German,
Wisent) ranged through Germany and is described in his account of the
Hercynian Forest; but the advance of civilization has almost exterminated
it, only a few small herds being maintained by the most rigid protection
in Russia and in the Carpathian Mountains. Of the Carnivora, the weasels,
martens, Fisher, Mink and Ermine are Boreal, as are the Wolverene
(_Gulo_) and the Grey Wolf (_Canis_), the three last-named extending also
into the Arctic zone. Essentially Boreal, though reaching and entering
the Sonoran, are the bears (_Ursus_), the red foxes (_Vulpes_), the
otters (_Lutra_) and the Old World shrews (_Sorex_), while the Star-nose
Mole (_Condylura_) and the mole-shrews (_Urotrichus_) do not extend
south of the Transition zone. Probable intruders from the south into the
Boreal subregion are the pumas, or “mountain lions,” which just enter
the subregion, the Canada Lynx (_Lynx rufus_) and one species of skunks
(_Mephitis_), the Raccoon (_Procyon lotor_), Badger (_Taxidea americana_)
and the American deer (_Odocoileus_). A large number of rodents are
characteristically Boreal: marmots, or woodchucks (_Marmota_), the
Sewellel (_Aplodontia rufa_), lemmings (_Myodes_), Jumping Mouse
(_Zapus_), the Canada Porcupine (_Erethizon dorsatus_) and the pikas,
“tailless or whistling hares” (_Ochotona_). Boreal rodents that enter the
Sonoran are the chipmunks (_Tamias_), beavers (_Castor_), meadow-mice
(_Microtus_), the Muskrat (_Fiber zibethicus_). The white-footed mice
(_Sitomys_) and the wood-rats (_Neotoma_) are southern rodents that reach
or enter the Boreal.
Between the Boreal subregion and the Sonoran region is the Transition
zone, which follows all the complex windings of the boundary lines. It
covers most of New England, New York, Pennsylvania and southern Ontario;
passing through southern Michigan and Wisconsin, it bends northward over
Minnesota and covers most of North Dakota, Manitoba and the plains of
the Saskatchewan, then turns abruptly southward and includes eastern
Montana and parts of South Dakota and Nebraska. Crossing Wyoming, it
follows around the northern edge of the Great Basin to the plains of the
Columbia. The three great mountain-systems carry the zone far to the
south and arms of it extend along the Appalachians to northern Georgia,
along the Rockies to New Mexico, and it follows the Sierras to southern
California. “The Transition zone, as its name indicates, is a zone of
overlapping Boreal and Sonoran types. Many Boreal genera and species here
reach the extreme southern limits of their distribution and many Sonoran
genera and species their northern limits. But a single mammalian genus
(_Synaptomys_) [one of the field mice] is restricted to the Transition
zone.... A number of species, however, seem to be nearly or quite
confined to this zone” (Merriam).
[Illustration: FIG. 61.—Upper figure, European Bison (_Bison bonasus_).
Lower figure, American Bison (_B. bison_).—By permission of the N.Y.
Zoölog. Soc.]
[Illustration: FIG. 62.—Wolverene (_Gulo luscus_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 63.—Wapiti or “Elk” (_Cervus canadensis_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 64.—Alaska Brown Bear (_Ursus middendorfi_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 65.—Moose (_Alce americanus_). Young male with
undeveloped antlers.—By permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 66.—Beaver (_Castor canadensis_).—By permission of
the N.Y. Zoölog. Soc.]
[Illustration: FIG. 67.—Woodland Caribou (_Rangifer caribou_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 68.—Red Fox (_Vulpus fulvus_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 69.—Rocky Mountain “Goat” (_Oreamnos montanus_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 70.—Ermine (_Mustela erminea_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 71.—Timber or Grey Wolf (_Canis nubilis_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 72.—Boreal Mammals. _A._ Black-footed Ferret
(_Mustela nigripes_). _B._ Otter (_Lutra canadensis_). _C._ Jumping Mouse
(_Zapus hudsonius_).—_A_ and _B_ by permission of the N.Y. Zoölog. Soc.
_C_, by permission of W. S. Berridge, London.]
[Illustration: FIG. 73.—Opossum (_Didelphis marsupialis_).—By permission
of the N.Y. Zoölog. Soc.]
The most characteristic portion of North America, zoölogically speaking,
is the Sonoran region of Dr. Merriam, the Warm Temperate of Dr. Allen.
It crosses the continent from ocean to ocean, its northern boundary
following for most of the way the 43d parallel of latitude, but over the
Great Plains and Great Basin, on each side of the Rocky Mountains and
the high plateaus, it extends to lat. 48°. On the south, it takes in the
greater part of Mexico, covering all of the table-land of that country,
the lowlands of which belong to the South American or Neotropical
region. The Sonoran is invaded from the north by the long branches
from the Boreal and Transition zones, which follow the three great
mountain-systems in the manner already explained, and the Mexican plateau
permits the similar invasion of Neotropical territory by the Sonoran
fauna. Characteristic Sonoran genera, none of which extend into the
Boreal, are the opossums (_Didelphis_), in the southern part a peccary
(_Tagassu_) or “Wild Texas Pig,” representative of a family of swine
quite different from the true pigs of the Old World, and an armadillo
(_Tatu_). A very isolated form is the Prong-horned Antelope (_Antilocapra
americana_); there are several species of the typically American deer
(_Odocoileus_) which differ in important respects from those of the
eastern hemisphere, and the Bison was very abundant until exterminated by
Man. Bison, antelope and deer also reach or extend into the Boreal zone,
but the former, or Wood Bison, is probably a different species from the
plains animal.
[Illustration: FIG. 74.—Prong-horned Antelope (_Antilocapra
americana_).—By permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 75.—Kangaroo-Rat (_Dipodomys philippii_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 76.—Thirteen-lined Spermophile (_Spermophilus
tredecimlineatus_).—By permission of the N.Y. Zoölog. Soc.]
The grey foxes (_Urocyon_), Coyote (_Canis latrans_), large Timber
Wolf (_Canis occidentalis_), the Caxomistle (_Bassariscus_), the Coati
(_Nasua_), Raccoon (_Procyon_), Badger (_Taxidea_), three genera of
skunks, pumas, several species of lynx and some bears (_Ursus_) represent
the Carnivora, though one species each of raccoon, skunk, badger, puma
and lynx range into the Boreal. The American types of shrews (_Blarina_)
and moles (_Scalops_ and _Scapanus_) are characteristic of the Sonoran,
though partially shared with the Boreal. A great many peculiar rodents
inhabit the Sonoran; cotton-rats (_Sigmodon_), pocket-gophers (_Geomys_,
etc.), several genera of the beautiful little kangaroo-rats (_Dipodomys_,
etc.); while the prairie-dogs (_Cynomys_), the white-footed mice
(_Sitomys_), wood-rats (_Neotoma_) and one genus of pocket-gophers
(_Thomomys_) are chiefly Sonoran, but have Boreal representatives.
The flying squirrels (_Sciuropterus_), true squirrels (_Sciurus_),
ground-squirrels (_Spermophilus_), rabbits (_Lepus_), wolves (_Canis_)
and otters (_Lutra_) have a very wide range through both the Boreal and
Sonoran, but have many more species in the latter region.
[Illustration: FIG. 77.—Grey Squirrel (_Sciurus carolinensis_).—By
permission of the N.Y. Zoölog. Soc.]
The Sonoran region may be divided into the upper and lower Sonoran zones,
which are demarcated by temperature and are of transcontinental extent.
Each of these zones may, in turn, be subdivided into _arid_ and _humid_
provinces, but our purpose does not necessitate entering into such
refinements.
[Illustration: FIG. 78.—Grey Fox (_Urocyon virginianus_).—By permission
of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 79.—Prairie Wolf or Coyote (_Canis latrans_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 80.—Raccoon (_Procyon lotor_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 81.—Virginia Deer (_Odocoileus virginianus_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 82.—Skunk (_Mephitis mephitis_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 83.—Mule Deer (_Odocoileus hemionus_).—By permission
of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 84.—Badger (_Taxidea americana_).—By permission of
the N.Y. Zoölog. Soc.]
[Illustration: FIG. 85.—Puma or Mountain Lion (_Felis concolor_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 86.—Lynx (_Lynx rufus_).—By permission of the N.Y.
Zoölog. Soc.]
[Illustration: FIG. 87.—Prairie-Dog (_Cynomys ludovicianus_).—By
permission of the N.Y. Zoölog. Soc.]
The Neotropical, which is the only region of the Neogæic realm, comprises
the West Indian islands, all of Central and South America and the
lowlands of Mexico, extending a short distance into southeastern Texas.
Of its four subregions, the most typical is (1) the _Brazilian_, which
includes not only Brazil, but all of South America east of the Andes and
as far south as Paraguay, and is a vast area of tropical forests. (2)
The _Chilian_ subregion takes in the west coast, the high Andes and the
southern end of the continent, south of the Brazilian subregion; it is
a country chiefly of open plains and high mountains, and a few deserts,
of which South America has less than any other continent, except Europe,
which has none. (3) The _Central American_ subregion reaches from the
Isthmus of Panama to Mexico, the lowlands of which are included and even
a small portion of southeastern Texas. (4) The _West Indian_ subregion
includes all the islands of that archipelago, except Trinidad, which is a
fragment of the continent, detached at a comparatively recent date; the
southern extremity of Florida also belongs to this subregion.
The two subregions into which continental South America is divided are
not altogether satisfactory and will doubtless require change when
the distribution of South American mammals has been more accurately
determined.
[Illustration: FIG. 88.—Map of the Neotropical region. (After Wallace.)
Mexico inaccurate; cf. Fig. 53, p. 147.]
[Illustration: FIG. 89.—Fox-like Wolf (_Cerdocyon gracilis_).—By
permission of W. S. Berridge, London.]
“Richness combined with isolation is the predominant feature of
Neotropical Zoölogy, and no other region can approach it in the number
of its peculiar family and generic types” (Wallace). Just as North
America has received many immigrants from the Old World, so it has sent
many migrants into South America, materially changing the character of
the Neotropical mammalian fauna, but these intruders may be readily
identified and almost seem to be out of place in their new surroundings.
Not all of these northern migrants were able to maintain their footing
in the southern continent and several became extinct during and at the
close of the Pleistocene epoch, as was even more markedly the case with
the southern forms which invaded the northern continent.
[Illustration: FIG. 90.—Spectacled Bear (_Tremarctos ornatus_).—By
permission of the N.Y. Zoölog. Soc.]
There are two families of monkeys in the forested areas of South America,
both very different from those of the Old World. One of these families,
the marmosets (Hapalidæ), differs from all other monkeys in several
particulars, most obvious of which are the long claws on the feet and the
non-opposable thumb. The second family (Cebidæ) comprises forms which are
superficially much more like those of the eastern hemisphere, but many of
them have prehensile tails, which are used as efficient grasping organs.
Insectivora are entirely absent from the South American continent, but
some shrews (_Blarina_) have entered Central America from the north and
a very curious genus is represented by one species in Cuba (_Solenodon
cubanus_) and another in Hayti (_S. paradoxus_). These remarkable animals
are, strange to relate, most nearly allied to the tenrecs (_Centetes_) of
Madagascar and by some authorities are placed in the same family.
[Illustration: FIG. 91.—_Solenodon cubanus._—By permission of the N.Y.
Zoölog. Soc.]
[Illustration: FIG. 92.—Argentine Skunk (_Conepatus gibsoni_).—By
permission of W. S. Berridge, London.]
[Illustration: FIG. 93.—Little Skunk (_Spilogale putorius_).—By
permission of W. S. Berridge, London.]
The Carnivora are quite numerous and varied and rather peculiar, but
they all belong to northern families and are the more or less modified
descendants of northern immigrants. The dogs (Canidæ) belong to
genera not represented elsewhere and form a considerable assemblage
of interesting types. There are no true wolves or foxes, but several
species of fox-like wolves (_Cerdocyon_), with bushy tails, are common,
especially in the plains regions. The Bush-Dog (_Icticyon venaticus_),
a small, short-legged animal, is very peculiar. The musteline or weasel
family (Mustelidæ) is rather scantily represented. There are no badgers
and but few skunks (_Spilogale_ and _Conepatus_); weasels are absent,
but their place is taken by the Grison (_Galera vittata_) and Tayra
(_Tayra tayra_) and in the far south _Lyncodon patagonicus_. These
animals are peculiar in having a lighter colouration on the back than
on the belly. There are two or three species of otter (_Lutra_). The
raccoons (_Procyon_) have a very wide range in South America, as in the
northern continent, and the curious, long-snouted coatis (_Nasua_), which
just enter the Sonoran region, are typically Neotropical. The Spectacled
Bear (_Tremarctos ornatus_) is the only member of the family that occurs
in South America and is confined to the highlands of Peru and Chili. The
cat family is quite numerously represented; the Jaguar (_Felis onca_),
which ranges from Texas to Patagonia, is a large spotted cat, rivalling
the Leopard in size and ferocity; the Ocelot (_F. pardalis_, Arkansas to
Paraguay) is smaller and streaked and blotched rather than spotted. The
pumas differ little from those of North America, and there are many small
cats, spotted, clouded and of solid colour, but no lynxes, which are
essentially northern types.
[Illustration: FIG. 94.—Tayra (_Tayra tayra_).—By permission of W. S.
Berridge, London.]
[Illustration: FIG. 95.—Kinkajou (_Potos caudivolvulus_), Central
America.—By permission of W. S. Berridge, London.]
[Illustration: FIG. 96.—Ocelot (_Felis pardalis_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 97.—Jaguar (_Felis onca_).—By permission of the N.Y.
Zoölog. Soc.]
[Illustration: FIG. 98.—Collared Peccary (_Tagassu tajacu_).—By
permission of the N.Y. Zoölog. Soc.]
Hoofed animals are not numerously represented in South America. The
only existing Perissodactyla of the western hemisphere are the tapirs
(_Tapirus_) of Central and tropical South America, a very remarkable
contrast to the ancient faunas, especially of the northern continent, as
will be shown in the sequel. The Artiodactyla are more varied, though
very scanty in comparison with those of the Old World; even North
America, which has but a poor representation of these animals, is much
richer than the southern continent, where, indeed, all the hoofed animals
are the descendants of comparatively recent immigrants from the north
and none are truly autochthonous. Members of three different artiodactyl
suborders occur in the Neotropical region; the peccaries (_Tagassu_)
extend through Central and South America to Paraguay, though also
entering the Sonoran region in Texas. Most interesting are the members of
the camel family, which are very distinct from the true Camel of Asia.
Tierra del Fuego and the Patagonian plains support great herds of the
Guanaco (_Lama huanacus_), which extends along the Andes to Ecuador and
Peru, where it is associated with the Vicuña (_L. vicunia_), a smaller
and more slenderly built species. The Vicuña does not range south of
Bolivia. Just as the mountain systems of North America carry the Boreal
and Transition faunas through nearly the whole breadth of the Sonoran
region, so the high Andes afford a pathway by which the mammals of the
south temperate zone extend their range to the equator.
[Illustration: FIG. 99.—Vicuña (_Lama vicunia_).—By permission of the
N.Y. Zoölog. Soc.]
[Illustration: FIG. 100.—Florida Deer (_Odocoileus virginianus
osceola_).—By permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 101.—Marsh Deer (_Blastoceros paludosus_), female.—By
permission of the N.Y. Zoölog. Soc.]
The suborder Pecora of the Artiodactyla is represented in the Neotropical
region only by the deer family (_Cervidæ_), of which there are several
genera (or subgenera), all of them North American as distinguished from
the Old World type, but some are so peculiar that they must have had a
relatively long South American ancestry. The Virginia Deer (_Odocoileus
virginianus_) of the northern United States is a comparatively large
animal, becoming much smaller in Florida and the Southwest. The type
extends through Mexico and Central America to Guiana and Peru, the
Neotropical forms being so small and having such weak antlers that
they are referred to separate species. Another type is the Marsh Deer
(_Blastoceros paludosus)_ of eastern South America, which has short,
stout antlers, each beam with two double bifurcations; there are other
species of the same genus, such as the Pampas Deer of Argentina (_B.
bezoarticus_). In the Andes of Peru and Chili and the forests of western
Patagonia are two species of a genus which bears the preposterous name of
_Hippocamelus_ and in which the antlers are simply forked. The vernacular
name of these animals is “Huemul.” Peculiarly Neotropical are the little
brockets, which hardly exceed a height of two feet at the shoulder, with
simple spike-like antlers not more than three inches long; the genus,
_Mazama_, has several species, one of which occurs as far north as the
state of Puebla in Mexico. “The smallest of all deer is the Chilian pudu
(_Pudua pudu_), a creature not much larger than a hare, with almost
rudimentary antlers” (Lydekker). Old World types of deer, such as the
Wapiti, Moose and Caribou, of the Boreal and Transition zones of North
America, are entirely absent from the Neotropical region.
[Illustration: FIG. 102.—Wood Brocket (_Mazama nemorivagus_).—By
permission of W. S. Berridge, London.]
[Illustration: FIG. 103.—Brazilian Tree Porcupine (_Coendou
prehensilis_).—By permission of the N.Y. Zoölog. Soc.]
South America has an astonishingly rich and varied assemblage of
rodents, both indigenous and immigrant, but the former are much the more
important, varied and abundant. Of the four divisions of the order,
all of which are represented, three are immigrants from the north and
the fourth is autochthonous, but this far outnumbers the other three
combined. The hares and rabbits have but very few species, one of which
occurs in Brazil and is separated by a very wide interval from the one in
Costa Rica, while the pikas are absent. Of the squirrel division, only
the true squirrels are found, and of these there are many species, the
ground-squirrels, marmots, prairie-dogs and beavers all being lacking.
In the same way the rat and mouse division is represented by a single
family. The vesper or white-footed mice (_Sitomys_) have invaded the
southern continent and a number of peculiar genera have arisen there, but
all of northern ancestry, such as the groove-toothed mice (_Rheithrodon_)
and the fish-eating rats (_Ichthyomys_). The voles, or meadow-mice, the
muskrats, jumping mice, kangaroo-rats and pocket-gophers of the northern
continent are all absent. While the immigrant suborders have thus but
one family each in South America, the case is very different with the
fourth or porcupine group, of which that continent is to-day, as it has
been for ages past, the headquarters. No less than six families and
twenty-nine genera are known, all of the genera and four of the families
being restricted to the Neotropical region. Contrast this assemblage with
the extreme scantiness of this group in North America, where but a single
genus, the Short-tailed or Canada Porcupine (_Erethizon_) represents it,
and that is a late immigrant from the south.
[Illustration: FIG. 104.—Neotropical rodents. _A._ Vizcacha
(_Viscaccia_). _B._ Paca (_Agouti paca_). _C._ Rock Cavy (_Cavia
rupestris_). _D._ Water-Hog, or Carpincho (_Hydrochærus_). _D_, by
permission of the N.Y. Zoölog. Soc. _A_, _B_, _C_, by permission of W. S.
Berridge, London.]
[Illustration: FIG. 105.—Chinchilla (_Chinchilla laniger_).—By permission
of W. S. Berridge, London.]
It would lead us too far to attempt a description of this horde of
curious and interesting rodents, so only a few of the more striking
and characteristic forms can be mentioned. There are two genera of
porcupines (_Coendou_ and _Chætomys_), both arboreal, which belong in
the same family as the North American _Erethizon_, but are distinguished
by their long, prehensile tails, which they use, as monkeys and opossums
do, for grasping and climbing. The very large family of the Octodontidæ
has 17 Neotropical genera and four others are found in Africa. The
Degu (_Octodon_) of Chili, Bolivia and Peru has the appearance of a
large rat with tufted tail; the tuco-tucos (_Ctenomys_) are extremely
abundant burrowers in Patagonia, where they honeycomb the ground over
wide areas. The spiny rats (_Echimys_ and _Loncheres_) are so called
from their appearance, not because they are related to the true rats;
they have numerous horny spikes through the fur of the back. The Coypu
(_Myocastor_) is a large, aquatic animal, remotely like the northern
Muskrat, and the Hutias (_Capromys_ and _Plagiodontia_) are arboreal
and found only in Cuba, Hayti and Jamaica. The chinchillas (_Chinchilla_
and _Lagidium_) of the Andes and the Vizcacha (_Viscaccia_) of the
Argentine plains have somewhat the appearance of hares, but with long
and bushy tails. The cavies, to which the familiar, misnamed Guinea-Pig
(_Cavia porcellus_) belongs, are a very characteristic family; besides
the true cavies, it includes the Patagonian Mara (_Dolichotis_), a large,
long-legged, long-eared, short-tailed creature, and the Water-Hog, or
Carpincho (_Hydrochærus_), an aquatic animal, as its name implies, and
much the largest of existing rodents; it occurs in the warmer regions,
south to Argentina. The heavy Paca (_Agouti_) and the slender-limbed
Agouti (_Dasyprocta_) make up another family. Altogether, this assemblage
of the porcupine-like suborder of rodents is a very remarkable one and in
no other region of the earth is anything like it to be found.
[Illustration: FIG. 106.—Hairy-rumped Agouti (_Dasyprocta
prymnolopha_).—By permission of W. S. Berridge, London.]
[Illustration: FIG. 107.—Three-toed Sloth (_Bradypus tridactylus_).—By
permission of the N.Y. Zoölog. Soc.]
With the exception of one genus of armadillos, which has invaded
Texas, the entire order of the Edentata is at present confined to the
Neotropical region, the so-called edentates of the Old World now being
removed to other orders. The Edentata, which were once far more varied
and abundant than they now are, comprise three groups of animals so
bizarre and strange that they seem more like fabulous creatures than
actual, living mammals. One group, or suborder, is that of the sloths
(Tardigrada), arboreal, shaggy animals, with short, almost monkey-like
head and no tail; their very long legs and hook-like feet make them
nearly helpless on the ground, but are very useful for hanging from the
branches of the trees, in which the creatures live. Indeed, the sloths
are the only mammals which habitually hang in a suspended position. Two
genera of sloths inhabit the tropical forests, between which the most
obvious difference is that in one (_Bradypus_) the forefoot has three
toes, and in the other (_Cholœpus_) two.
[Illustration: FIG. 108.—Two-toed Sloth (_Cholœpus didactylus_).—By
permission of W. S. Berridge, London.]
The suborder of the anteaters (Vermilingua) is more varied, and is the
only one of the order to which the term “edentate” applies strictly, for
they alone in the order are altogether toothless. The great Ant-Bear
(_Myrmecophaga jubata_), which may reach a total length of seven feet,
has an extravagantly long, slender and nearly cylindrical head, long,
shaggy, black and white hair and an immense, bushy tail; the forefeet are
armed with huge, sharp-pointed claws, which are used for tearing open
ant-hills, and when occasion arises, as formidable weapons of defence,
for the Ant-Bear can successfully repulse even the Jaguar. In walking,
the claws are curved inward and the preposterous beast rests his weight
upon the outside edges of the forefeet, while the hind feet apply the
sole to the ground, as does a bear or raccoon. The Collared Anteater
(_Tamandua_) is much smaller and mainly arboreal in habits. It has a
short-haired, black body, with a white stripe down the back, white neck
and limbs, a colour-pattern which gives to the animal the appearance of
wearing a close-fitting black jacket; the long tail, which has some cross
bars, is short-haired, very different from the extremely bushy tail of
the Ant-Bear. The little Two-toed Anteater (_Cyclopes didactylus_),
hardly larger than a rat, is exclusively arboreal and has a prehensile
tail, like so many other South American mammals. Sloths and anteaters are
forest animals and are not found west of the Andes or south of Paraguay.
[Illustration: FIG. 109.—Ant-Bear (_Myrmecophaga jubata_).—By permission
of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 110.—Collared Anteater (_Tamandua tetradactyla_).—By
permission of the N.Y. Zoölog. Soc.]
[Illustration: FIG. 111.—Six-banded Armadillo (_Dasypus sexcinctus_).—By
permission of the N.Y. Zoölog. Soc.]
The third existing suborder of edentates is that of the armadillos
(Dasypoda), which have a very complete armour of bony scutes,
ossifications in the skin, covered with scales of horn. They are all more
or less burrowers in habit and omnivorous in diet, eating roots, insects,
worms, etc.; the extraordinary rapidity with which they burrow into
the ground is almost their only way of escape from pursuit, but in one
genus, _Tolypeutes_, the animal can roll itself into a ball, completely
protected by mail all around. The armadillos are much more varied than
the anteaters or sloths and have a wider geographical range, extending
from Texas to Patagonia. The head, which is long-snouted, is protected
by a shield made up of numerous horn-covered plates of bone, and the
tail is encased in a tubular sheath of more or less regular rings, each
ring of bony plates and horny scales. The body-shield, or carapace,
which covers the back and sides, consists of an anterior and posterior
buckler, in which the plates are immovably attached to one another by
their edges, and between the two is a series of movable, overlapping
bands, the number of which varies in the different genera. In the little
Pichiciago (_Chlamydophorus truncatus_) the head and back are covered
with four-sided plates of horn, the bony scutes being small and thin
and much reduced. The carapace has no bucklers, but about 20 transverse
rows of plates, and is attached along only the middle line of the back
and beneath it the body is covered with silky, white fur; the rump is
covered with a solid shield of bone, placed nearly vertically and covered
with thin scales, and is notched below for the tail, altogether a most
exceptional arrangement. Seven or more distinct genera of armadillos are
found in the Neotropical region and they display a great range in size;
the Giant Armadillo of Brazil (_Priodontes_) is a yard or more in length,
while the little _Zaëdyus_ of Patagonia is smaller than a rabbit and,
least of all, the Pichiciago is but five inches long.
[Illustration: FIG. 112.—Nine-banded Armadillo (_Tatu novemcinctus_).—By
permission of the N.Y. Zoölog. Soc.]
Two families of marsupials occur in South America. The opossums are
much more numerous and varied than in North America; three genera and a
large number of species, some not larger than mice, range through the
forested parts of the continent. Of particular interest is the little
_Cænolestes_, which has two species, with two enlarged lower front
teeth, the sole survivors of a group which is abundantly represented in
the Tertiary deposits of Patagonia.
The fauna of the Central American subregion is less rich and
characteristic than that of the Brazilian and is, to a certain extent,
transitional to that of the Sonoran region of North America, several
genera proper to the latter region extending into it, which are not known
to pass the Isthmus of Panama, such as shrews, a fox and one of the
pocket-mice. The West Indian islands are exceedingly poor in mammals,
a great contrast to the East Indian, or Malay, Archipelago; only a few
rodents, insectivores and bats occur in them.