312 Evolution? The Fossils Say YES!
true for an untrained, unobservant amateur, but anyone who knows bat anatomy can tell
how primitive these fossils are. For one thing, the earliest bats did not yet have the ear
structure necessary for the modern system of echolocation that bats use to catch insects
on the wing. Their large skulls and eyes show that they probably hunted by day using
sight, not at night using echolocation. In addition, Eocene bats have many other primitive
features of the skull, hands, and feet that are not found in any other living bat. They may
have had wings, but to someone who actually knows their fossils and mammals, a bat is
not just a bat!
Lions and Tigers and Bears, Oh My!
A lion’s work hours are only when he’s hungry; once he’s satisfied, the predator and
prey live peacefully together.
—Chuck Jones, AnimatorBats and rats usually don’t interest too many people (except as pests) nor do most of the
other orders of mammals, such as xenarthrans (which have an excellent fossil record with
many transitional fossils of ground sloths and huge armored armadillos) or the insectivores
(which have an amazing fossil record going back to the Cretaceous). So we will not dwell
on these examples further for space reasons, but we will focus on two large mammal groups
that do excite people: the hoofed mammals (or ungulates), subject of the next chapter, and
the carnivorous mammals.
Lots of people love cats and dogs, and many are pet owners, so carnivores are near
and dear to many hearts. Those science documentaries on cable TV and the children’s
books about prehistoric mammals love to show saber-toothed cats, dire wolves, and cave
bears, but there is far more to carnivore evolution than just these glamorous creatures.
Carnivorous mammals are usually not as commonly fossilized as their herbivorous prey.
Because it usually takes many prey animals to support one predator, the population num-
bers of carnivores are always small, and their chances of fossilization are further dimin-
ished. Nevertheless, they have an excellent fossil record going back through the entire
Cenozoic, with far more diversity of forms than can be seen today with modern cats, dogs,
bears, and their relatives. We can trace the living order Carnivora back to the most primi-
tive groups, an assemblage of highly primitive carnivorans known as miacids known from
the Paleocene of the northern continents (fig. 13.14). All of these creatures were small,
archaic weasel-sized creatures that look nothing like their descendant families but had all
the hallmarks of the Carnivora. In the next few million years of the Eocene and Oligocene,
we soon see the divergence of a number of modern families (fig. 13.15). For example, the
dogs appear in the middle Eocene and soon have an incredible evolutionary radiation of
dozens of genera and hundreds of species. They evolved into a wide spectrum of forms,
from some that were smaller than weasels (Hesperocyon) to the huge borophagine dogs,
hyena-like forms with crushing teeth for breaking bones—far more diversity than dogs
show today (fig. 13.16).
True cats appear in the early Oligocene with Pseudailurus, a creature that looked more
like a weasel than a cat (fig. 13.17). But by the Miocene, they began to take on their catlike