Mexico weekly ledger., 1876-11-09
Some Extinct American Animals.

creation, its opponents were wont to
ask triumphantly for missing links. If
species are the result of gradual deyel-
opment by progressive variation. thew
said, we ought to find an abundance Of
Intermediate forms; where are thew?
The advocates of evolution could on
" reply: They will appear when sought
for. Darwin even ventured the proDh-
ecy that in course of time links would
be found connecting the extremely
specialized one-toed horse with the nor
NAL four and five-toed mammals. The
readers of the Scientific Ameyscan know
how completely the prophecy has been
fulfilled in the numerous and increas-
ingly specialized horse-like creatures
which roamed over our Western plains
during the tertiary period of geology.
At the beginning OF the period the four
toed orohippus was most like the horse
that was to be, though it exhibited MANY
unhorselike characteristics. From that
time down to the present the chain of
development is complete, the precursors
of the horse steadily growing more and
more horselike in head, and foot, and
general structure of body andlimb. In
the middle tertiary, the ~mesoaippus
had but three toes, a slender splint of
bone being the only vestige of the lost
toe; and in the miohippus the splint
had vanished. Later the three neatly
equal toes of the miohippus had be-
come three very unequal toes in the
hipparlon, the large middle toe being
the main II not the entire support Of
the animal. AT the close of the period,
the prevailing form was a true horse,
in which the dwindled and useless side
toes of the h~ipparion had ceased to ex-
list as toes, appearing only as slender
splints under the skin. In the modern
horse these splints are sometimes seen,
Hattesting its relationship with the horses
of prehistoric times. P
Similar, if not positive, evidence of
evolution is borne by the remains of
taplrs, rhlnocerOses, and other hoOfed
animals. In eocene times the most
prominent of the unequaled-toed ungu-
lates were the hyrachyus and the palfeo-
syops, the former allied to the lophio-
dons and tapirs, the latter to the palseo-
theriums of the European t~ertiaries.
Both these families embraced animals
varying in size from a small ~rhinoceros
to a peccary. Ia the miocene period,
these families attained a great develop
ment in form, variety and size; The
group became more distinctly separated
from each other, and some of them
possessed remarkably specialized char
acter. There were, however, no true
tapirs, which afterwards became so nu.
merOus. The ascendant forms Of this
period were rhinocerotic, represented
by the diceratherum, with it's pair of
horns side by side On the nose, and the
very interesting genus hyracodon, which
furnishes a connecting link between the
pal9otheroid animals of the eocene and
the true ~rhinoceros of the pliocene. The
miocene period also produces several
species of q more perfect ~rhinoceros,
still hornless. Bat more remarkable
than any of these, indeed in some re-
spects the most remarkable of all the
animals brought to light in the strata
of the West, were a number of species
OF grotesque appearance and gigantic
size, resembling the existing rhinoceros
in general appearance, but larger, some
of them approaching the elephant in
size and length of limb. They have
been named titanotheriums, brontoth-
eriums, and symborodons, and appear
to have died out during the milo enc
epoch. While they lived they must have
played the part of the then extinct uin-
tatherium OF the eocen (of which more
Directly, and that afterwards filled by
the mastodons and elephants of later
ages.
Very interesting evidence of evolu-
ton is also furnished by the equal-toed
hoofed animals, represented now by
pigs, hippopotami, camels, chevrotains,
deer, antelopes, sheep and oxen. Their
remains appear but sparingly during
the eOcene period, but become album
dant in the miocene. During this period
the first mentioned family were repre-
sented chiefly by huge swine-like crea-
lures, some of which approached the
hippopotamus in size. There was also
an allied four-toed form, more like true
pigs; but all the species were of the
peccary type. The sole existing sur
vivor of the form on this continent is
the South American peccary, apparent
ly an unmodifed remnant of the old
miocene fauna.
A much more remarkable family was
the oreodantid8, which began in the
later eocene, extended through the milo
Gene, when they swarmed enormously,
dying out in the early pliocene. In
nearly all points of structure, they were
Intermediate between ruminants and
swine, furnishing a complete line of
transition between those now widely
separated groups. Their remains are
found in great abundance, both in spe-
cies and individuals; and a gradual
modification, corresponding with the
chronological position, can be traced
from the earlier, o generalized forms
to the latest and most specialized; thus
4atfording one of the most complete
schains of evidence yet found in favor
Of progressive alteration of form, not
only of specific but of generic import
ance, through advancing ages.
Exceedingly suggestive, too, is the
history of the camelida as exhibited IN
our tertiary strata. Here was appa-