Bossies and Blowholes 345body!), which clearly did not function for locomotion. Like the vestigial hind limbs of mod-
ern whales buried inside the body, these tiny limbs were functionless relicts of the day when
“whales” did walk on land. Since this discovery, other archaeocetes such as Takracetus and
Gaviocetus have been found to retain vestigial hind limbs.
The most important discovery occurred when Thewissen et al. (1994) discovered and
described Ambulocetus natans, whose name means “walking swimming whale.” Found in
middle Eocene marine beds of Pakistan, it was about the size of a sea lion (fig. 14.18), with
functional flippers on both its forelimb and huge hind limb (which still had vestigial hooves
as well). Its skull and teeth, however, were still like those of mesonychids. On the basis of
its highly flexible vertebrae, Thewissen et al. (1994) suggested that Ambulocetus swam with
an up-and-down flexure of its body, similar to the swimming motion of an otter rather than
paddling with its feet like a penguin or seal or wriggling side to side like a fish. This is a
precursor to the up-and-down motion of a whale’s tail flukes as it swims through the water.
Further discoveries (mostly in the middle Eocene of Pakistan) followed one after
another. Dalanistes, for example, had fully functional front and hind limbs with webbed feet
and a long tail but was much more whalelike with a longer snout. Rodhocetus was even more
like a dolphin, yet still retained functional hind limbs. Indohyus, on the other hand, provides
FIGURE 14.17. Ankle bones of middle Eocene whale Rodhocetus balochistanensis (left) and Artiocetus clavis (right)
from Pakistan, compared with those of the pronghorn Antilocapra americana (center). Note double-pulley
astragalus characteristic of mammals of the order Artiodactyla. (Photo courtesy P. D. Gingerich, University of
Michigan Museum of Paleontology)