Bossies and Blowholes 339how they evolved into a wide diversity of forms in the Oligocene and Miocene. For space
reasons, we’ll look at just two examples, the camels and the giraffes.
Most people are surprised to learn that extinct camels did not have humps and that
the camel family evolved in isolation in North America (fig. 14.13A). They only escaped
this continent in the late Cenozoic when they reached South America 3 million years ago to
evolve into llamas, guanacos, and vicuñas, and Eurasia about 7 million years ago, where
they evolved into the African dromedary and the Asian Bactrian camels. After all this suc-
cess, they vanished from their ancestral North American homeland at the end of the last ice
age 10,000 years ago. Fossil camels are also surprising in their amazing array of ecological
types, far exceeding the limited forms we see today (Honey et al. 1998). The earliest camels
were tiny rabbit-sized creatures (Poebrodon) that are known from isolated teeth and jaws
from the late middle Eocene of Utah, Texas, and California. But by the late Eocene and early
Oligocene they had evolved into sheep-sized creatures known as Poebrotherium (Prothero
1996), which are common in the Big Badlands of South Dakota. Poebrotherium has all the
hallmarks of a typical early camel: very high-crowned selenodont teeth, long limbs that were
(B)
ProcamelusPoebrotheriumProtylopusMioceneOligoceneEoceneFoot TeethFIGURE 14.13. (Continued )