both
in Europe and North America. Amongst the Odd-toed Ungulates the
most important are the Rhinoceroses, of which three species are
known to have existed in Europe during the Post-Pliocene period.
Two of these are the well-known Pliocene forms, the _Rhinoceros
Etruscus_ and the _R. Megarhinus_ still surviving in diminished
numbers; but the most famous is the _Rhinoceros tichorhinus_
(fig. 263), or so-called "Woolly Rhinoceros." This species is
known not only by innumerable bones, but also by a carcass, at
the time of its discovery complete, which was found embedded in
the frozen soil of Siberia towards the close of last century,
and which was partly saved from destruction by the exertions of
the naturalist Pallas. From this, we know that the Tichorhine
Rhinoceros, like its associate the Mammoth, was provided with
a coating of hair, and therefore was enabled to endure a more
severe climate than any existing species. The skin was not thrown
into the folds which characterise most of the existing forms;
and the technical name of the species refers to the fact that
the nostrils were completely separated by a bony partition. The
head carried two horns, placed one behind the other, the front
one being unusually large. As regards its geographical range,
the Woolly Rhinoceros is found in Europe in vast numbers north
of the Alps and Pyrenees, and it also abounded in Siberia; so
that it would appear to be a distinctly northern form, and to
have been adapted for a temperate climate. It is not known to
occur in Pliocene deposits, but it makes its first appearance
in the Pre-Glacial deposits, surviving the Glacial period, and
being found in abundance in Post-Glacial accumulations. It was
undoubtedly a contemporary of the earlier races of men in Western
Europe; and it may perhaps be regarded as being the actual
substantial kernel of some of the "Dragons" of fable.

[Illustration: Fig. 263.--Skull of the Tichorhine Rhinoceros, the
horns being wanting. One-tenth of the natural size. Post-Pliocene
deposits of Europe and Asia.]

The only other Odd-toed Ungulate which needs notice is the so-called
_Equus fossilis_ of the Post-Pliocene of Europe. This made its
appearance before the Glacial period, and appears to be in reality
identical with the existing Horse (_Equus caballus_). True Horses
also occur in the Post-Pliocene of North America; but, from some
cause or another, they must have been exterminated before historic
times.

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