In the Miocene we find the various groups diverging still further
from each other and from the extinct stocks. Definite wolves and
foxes abound in America, and the bear, civet, and hyaena are
represented in Europe, together with vague otter-like forms. The
dog-family seems to have developed chiefly in North America. As
in the case of the Ungulates, we find many strange side-branches
which flourished for a time, but are unknown to-day. Machoerodus,
usually known as "the sabre-toothed tiger," though not a tiger,
was one of the most formidable of these transitory races. Its
upper canine teeth (the "sabres") were several inches in length,
and it had enormously distensible jaws to make them effective.
The great development of such animals, with large numbers of
hyaenas, civets, wolves, bears, and other Carnivores, in the
middle and later Tertiary was probably the most effective agency
in the evolution of the horse and deer and the extinction of the
more sluggish races. The aquatic branch of the Carnivores (seals,
walruses, etc.) is little represented in the Tertiary record. We
saw, however, that the most primitive representatives of the
elephant-stock had also some characters of the seal, and it is
thought that the two had a common origin.
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