There has been much research over the past 20 years to try to determine the origin of whales.

Paleontologists have thought for some time that whales were descended from the artiodactyls, the group that includes living cows, deer and pigs, but no one was sure exactly which type of artiodactyl was most closely related to the whales.

A paper published recently in the journal Nature suggests that an obscure artiodactyl family called the Raoellidae might be the ancestor.

Raoellids were small four-footed animals that lived in southern Asia about 45 million years ago. At first glance, they don't appear to have much in common with whales.

But when Hans Thewissen of Northeastern Ohio Universities College of Medicine and his colleagues examined one of the ear bones from a raoellid called Indohyus, they found that the bone had a thickened structure on one side, a feature called an involucrum.

The involucrum is an important structure. Whales have a very thick, heavy involucrum, which is a key part in allowing whales to hear underwater. The involucrum is only found in whales and dolphins; no other mammals have it (not even other mammals that live in the ocean).

The fact that Indohyus has an involucrum tells us that it must be closely related to the whales.

Related Virginia science Standards of Learning: 3.4, 3.6; 5.2c, 5.6c; LS.10; LS.14; PS.6c; PS.8; ES.2; ES.10; ES.11; BIO.2b; BIO.7; BIO.8.