Biology Now, 2e

Whale Hunting ■ 199

improved function in a competitive environ-

ment. By being able to easily wade and dive in

water, Indohyus had an advantage over other

organisms in escaping predators and accessing

plants to eat on the river floor. Adaptive traits

take many forms, from an anatomical feature

thick bones,” says Cooper, now an assistant

professor at Northeast Ohio Medical Univer-

sity. Modern animals that live in shallow water,

such as manatees and hippos, also have thick

bones, which help prevent them from floating

and enable them to dive quickly (Figure 11.9).

“It isn’t just isolated to whales,” says Cooper.

“Bones have thickened again and again as

different groups of vertebrates entered the

water. When you trace back through the fossil

record, there is a pretty good correlation

between thickness of bone and whether some-

thing was living in the water.”

Indohyus’s thick bones are an example of an

adaptive trait, a feature that gives an individual

Figure 11.8

Comparing the skulls and jaws of fossilized Indohyus and a modern hippopotamus

These organisms’ teeth indicate their ability to eat plant material.

Crushing basins

Crushing

basins

Crushing basins

The molars of Indohyus (top left) are similar to

the shape of molars in contemporary aquatic

plant-eating animals like hippos (top right and

bottom left). These molars have crushing basins

for grinding up tough plant fibers.

Lisa Cooper is an assistant professor at Northeast

Ohio Medical University in the Department of

Anatomy and Neurobiology. She earned her PhD in

Thewissen’s lab.

LISA COOPER