Mammalian Explosion 313FIGURE 13.14. The most primitive true carnivorans are known as miacids, which were shaped roughly like
weasels or raccoons, but were much more primitive. They were probably ancestral to nearly all living
carnivorans. (Drawing by Carl Buell)
characteristics and evolved a variety of forms, including several different acquisitions of
saber-like canines. In addition, there was an earlier family of catlike forms known as nim-
ravids, which parallel cat evolution in many ways (including the evolution of several “saber-
toothed” forms) but are unrelated to cats.
Bears have a history going back to the early Oligocene as well, but nearly all the early
bears were small badger-like forms that then developed into fast-running dog-shaped
forms like Hemicyon. Only late in their evolution did bears become large and develop teeth
for an omnivorous diet. The fossil record of the mustelids (weasels, skunks, otters, bad-
gers, wolverines, and their kin) and of raccoons and their relatives are also quite good
(see Baskin 1998a, 1998b), although all the early members of these families are very primi-
tive and would look nothing like their living descendants if you saw them today. Neverthe-
less, the details of their teeth, skulls, and skeletons are highly distinctive and unmistakable.
Considering their rarity, the fossil record of most carnivorans is remarkably good, and