) in the later Eocene
period. The Paebrotherium, a small animal about two feet long, is
followed by Pliauchenia, which points toward the llamas and
vicunas, and Procamelus, which clearly foreshadows the true
camel. In the Pliocene the one branch went southward, to develop
into the llamas and vicunas, and the other branch crossed to
Asia, to develop into the camels. Since that time they have had
no descendants in North America.
The primitive giraffe appears suddenly in the later Tertiary
deposits of Europe and Asia. The evidence points to an invasion
from Africa, and, as the region of development is unknown and
unexplored, the evolution of the giraffe remains a matter of
speculation. Chevrotains flourished in Europe and North America
in the Oligocene, and are still very primitive in structure,
combining features of the hog and the ruminants. Primitive deer
and oxen begin in the Miocene, and seem to have an earlier
representative in certain American animals (Protoceras), of which
the male has a pair of blunt outgrowths between the ears. The
first true deer are hornless (like the primitive muskdeer of Asia
to-day), but by the middle of the Miocene the males have small
two-pronged antlers, and as the period proceeds three or four
more prongs are added.
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