Certainly it is a marvellous fact in the history
of the Mammalia, that in South America a native horse
should have lived and disappeared, to be succeeded in after-
ages by the countless herds descended from the few introduced
with the Spanish colonists!
The existence in South America of a fossil horse, of the
mastodon, possibly of an elephant, [4] and of a hollow-horned
ruminant, discovered by MM. Lund and Clausen in the
caves of Brazil, are highly interesting facts with respect to
the geographical distribution of animals. At the present
time, if we divide America, not by the Isthmus of Panama,
but by the southern part of Mexico [5] in lat. 20 degs., where
the great table-land presents an obstacle to the migration of
species, by affecting the climate, and by forming, with the
exception of some valleys and of a fringe of low land on
the coast, a broad barrier; we shall then have the two
zoological provinces of North and South America strongly
contrasted with each other. Some few species alone have
passed the barrier, and may be considered as wanderers from
the south, such as the puma, opossum, kinkajou, and peccari.
South America is characterized by possessing many peculiar
gnawers, a family of monkeys, the llama, peccari, tapir,
opossums, and, especially, several genera of Edentata, the
order which includes the sloths, ant-eaters, and armadilloes.
North America, on the other hand, is characterized (putting
on one side a few wandering species) by numerous peculiar
gnawers, and by four genera (the ox, sheep, goat, and antelope)
of hollow-horned ruminants, of which great division
South America is not known to possess a single species.
Formerly, but within the period when most of the now existing
shells were living, North America possessed, besides
hollow-horned ruminants, the elephant, mastodon, horse, and
three genera of Edentata, namely, the Megatherium, Megalonyx,
and Mylodon.
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