The primitive family which gave birth to the
horse also gave us, as we saw, the tapir and the rhinoceros. We
find ancestral tapirs in Europe and America during the Tertiary
period, but the later cold has driven them to the warm swamps of
Brazil and Malaysia. The rhinoceros has had a long and
interesting history. From the primitive Hyrochinus of the Eocene,
in which it is dimly foreshadowed, we pass to a large and varied
family in the later periods. In the Oligocene it spreads into
three great branches, adapted, respectively, to life on the
elevated lands, the lowlands, and the water. The upland type
(Hyracodon) was a light-limbed running animal, well illustrating
the close relation to the horse. The aquatic representative
(Metamynodon) was a stumpy and bulky animal. The intermediate
lowland type was probably the ancestor of the modern animal. All
three forms were yet hornless. In the Miocene the lowland type
(Leptaceratherium, Aceratherium, etc.) develops vigorously, while
the other branches die. The European types now have two horns,
and in one of the American species (Diceratherium) we see a
commencement of the horny growths from the skull.
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