340 Evolution? The Fossils Say YES!
nearly fused into a cannon bone, and the signature features of the skull and skeleton as well
(fig. 14.13B). Yet its proportions looked more like those of an antelope or a gazelle, and it
apparently had no hump either. In the late Oligocene and early Miocene, camels under-
went an explosive evolutionary radiation (fig. 14.13A) into relatively short-limbed varieties
(protolabines and miolabines); tiny delicate gazelle-like forms with extraordinarily high-
crowned teeth (stenomylines); long-legged, long-necked forms that looked much like the
modern guanaco or vicuña (aepycamelines); and even a group that evolved long necks and
performed the roles of treetop browsers that giraffes occupied in the Old World. Some of
these late Miocene and Pliocene “giraffe-camels” were huge as well, with appropriate names
like Gigantocamelus and Titanotylopus. Then, after spreading to Eurasia and South America in
the late Miocene and Pliocene, camels dropped in diversity during the ice ages, and only a
few species were left when they vanished from North America 10,000 years ago.
For our final example from the artiodactyls, let us consider the giraffe. As we have been
pointing out all along, the modern representatives of many mammalian families are very
atypical of most of the members of the family during its evolution. Most fossil rhinos did not
have horns, most fossil camels did not have humps, and most fossil giraffes did not have long
necks. Extinct giraffids (Solounias 2007) sported a wide diversity of horn shapes and body
sizes (fig. 14.14). Most fossil giraffes looked more like the short-necked okapi (fig. 14.14B), a shy
white-and-brown-striped denizen of the African rain forests, and the only other living giraf-
fid. Others, like Sivatherium, got to be huge and heavy with moose-like palm-shaped horns. In
the late Miocene, we finally see the lineage that leads to the modern Giraffa. Although the fos-
sil teeth are common enough, complete skeletons with the neck vertebrae are rare, so we can
see how the lineage evolved, but didn’t yet have fossils to show how the neck got longer. The
oldest known fossils of the genus Giraffa jumae from the late Miocene of Africa already seems
to have a long neck, so we need to seek fossils from earlier in the Miocene. Nikos Solounias
(1999) has shown the mechanisms by which the neck lengthens, and the prevailing ideas have
to be revised. Giraffes lengthen each vertebra somewhat but actually add an extra vertebra to
the neck, then shift the last neck vertebra to the shoulder region. This is why the giraffe neck
begins behind the forelimbs and why giraffes have their distinctive posture with the legs out
in front and the neck balanced almost over the center of the body, rather than sticking for-
ward all the time as in most mammals. Finally, Solounias has just described a description of
a classic transitional form (fig. 14.15): a giraffe fossil with an intermediate-length neck, longer
than that of the okapi and the other extinct forms but shorter than that of the living giraffes.
For so many years, people have speculated about how giraffes got their long necks, and now
we finally have the fossils to show exactly how it happened! Once again, the fossil record has
yielded a transitional form that the creationists claimed could never exist.
Walking Whales
These dogmatists, who by verbal trickery can make white black, and black white,
will never be convinced of anything, but Ambulocetus is the very animal that they
proclaimed impossible in theory. . . . I cannot imagine a better tale for popular presen-
tation of science or a more satisfying, and intellectually based political victory over
lingering creationist opposition.
—Stephen Jay Gould, “Hooking Leviathan by Its Past”