This Latter Tooth Greatly Interested Me, [3] And I Took
Scrupulous Care In Ascertaining That It Had Been Embedded
Contemporaneously With The Other Remains; For I Was Not
Then Aware That Amongst The Fossils From Bahia Blanca
There Was A Horse's Tooth Hidden In The Matrix:
Nor was it
then known with certainty that the remains of horses are
common in North America.
Mr. Lyell has lately brought
from the United States a tooth of a horse; and it is an
interesting fact, that Professor Owen could find in no species,
either fossil or recent, a slight but peculiar curvature
characterizing it, until he thought of comparing it with my
specimen found here: he has named this American horse Equus
curvidens. 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. Within nearly this same period (as
proved by the shells at Bahia Blanca) South America possessed,
as we have just seen, a mastodon, horse, hollow-
horned ruminant, and the same three genera (as well as
several others) of the Edentata. Hence it is evident that
North and South America, in having within a late geological
period these several genera in common, were much
more closely related in the character of their terrestrial
inhabitants than they now are.
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