Bossies and Blowholes 343People are startled to learn that most fossil rhinos didn’t have horns, most fossil camels
didn’t have humps, and most fossil giraffes had short necks. But they are even more sur-
prised to learn that whales are related to hoofed mammals and are descended from a group
of carnivorous hoofed mammals. In debates, creationists love to exploit this public ignorance
of the fossil record and zoology by putting up a slide of “Bossie” the cow and “Blowhole”
the whale and a ridiculous cartoon of an intermediate between a cow and a whale. But when
we said that whales are descendants of ungulates, we did not say “cows.” Apparently, when
creationists hear the words “hoofed mammal,” cows are the only kind they can think of.
Actually, hippos would be better models for a modern relative of whales, and they are not
nearly so different from whales (both are large and aquatic).
Ever since people realized that whales and dolphins were mammals, they have specu-
lated about how they might have evolved from land-dwelling mammals and from which
group of mammals they originated. By the 1830s and 1840s, specimens of huge primitive
whales known as archaeocetes (fig. 14.16) were being discovered in middle Eocene beds of
Alabama, but these specimens were fully aquatic, with flippers and tail flukes and a sinuous
24-meter-long (80 foot) body. Clearly, the origin of whales must have occurred before the
middle Eocene, but nothing was known of their fossil record prior to that time. In 1966, Leigh
van Valen and others had shown that the skulls and teeth of primitive whales looked very
much like the predatory archaic hoofed mammals known as mesonychids. Even though
mesonychids were land mammals with hooves, there were many similarities in the skull
and skeleton (especially the large, serrated triangular bladelike teeth) that suggested close
relationship with archaeocete whales. Yet for over a century, there were no transitional fossils
known between mesonychids and archaeocetes.
Until very recently, paleontologists were comfortable with the idea that whales were
related to mesonychids, and the fossil evidence seemed to bear this out. Then, in the late
1990s, molecular studies showed that among living mammals, the artiodactyls (and par-
ticularly the hippos) were the nearest relatives of the whales. This wasn’t too surpris-
ing because artiodactyls and whales are very closely related on the ungulate cladogram
(fig. 14.1), although we always thought they were sister taxa, not that whales were nested
within artiodactyls (Prothero et al. 1988). But in 2001, two independent groups of scientists
(Gingerich et al. 2001; Thewissen et al. 2001) found specimens of early whales that preserved
the ankle region (fig. 14.17). Amazing as it seems, these fossils clearly showed that early
whales had feet bearing ankles with the characteristic double-pulley astragalus, the signa-
ture feature of the whole order Artiodactyla. Since then, we’ve rethought the evidence, and
now most scientists would agree that whales are a group that evolved from the hippo-pig
lineage within artiodactyls and that mesonychids are the distant relatives of both whales and
artiodactyls (Geisler and Uhen 2005).
The breakthrough in our understanding of whale ancestry occurred when scientists
began to collect fossils in the lower Eocene beds of Pakistan. In 1983, Phil Gingerich and
colleagues described Pakicetus, based on a skull with an archaeocete braincase but lacking
ears that were capable of echolocation and with teeth intermediate between those of meso-
nychids and archaeocetes (fig. 14.16). Pakicetus came from river sediments bordering shallow
seaways, suggesting that it might have been a semiaquatic predator that waded in rivers
part-time to find food. The skeleton of Pakicetus is still quite wolflike, with long slender
limbs and a tail, so it still resembles a mesonychid in most features. The chemistry of its
bones showed it lived in freshwater.