336 Evolution? The Fossils Say YES!
divide not the hoof, therefore they are unclean unto you. And the swine, because it
divideth the hoof, yet cheweth not the cud, it is unclean unto you; ye shall not eat of
their flesh, nor touch their dead carcass.
—Deuteronomy 14:7–8After the Perissodactyla, the second great living order of hoofed mammals is the even-toed
hoofed mammals, or Artiodactyla. They are “even toed” or “cloven hoofed” because the axis
of symmetry of the foot runs between the third and fourth toes, and so they usually have
either two toes or four. Today, they are the most diverse and abundant ungulates on the
planet, with over 190 living species, including pigs, peccaries, hippos, camels and llamas,
deer, pronghorns, giraffes, sheep, goats, cattle, and dozens of species of antelope (fig. 14.11).
Nearly every domesticated animal we eat is an artiodactyl (pigs, sheep, goats, cattle, and
deer), and they provide us with all of our milk (whether from a cow, goat, or camel) and wool
(from either sheep or alpacas). Almost every large herbivore you might see in East Africa is
an artiodactyl except for zebras, rhinos, and elephants. Artiodactyls are indeed a modern
success story, yet they acquired that dominance gradually as the odd-toed perissodactyls
(especially horses, rhinos, tapirs, and brontotheres) dominated in the Eocene and gradually
were displaced, while artiodactyls (especially the ruminants, such as camels, sheep, goats,
and cattle) with their superior mode of digestion came to dominate the earth.
FIGURE 14.11. Evolutionary history of the even-toed hoofed mammals, or artiodactyls. (Drawing by C. R.
Prothero; from Prothero 1994b)