The end of the Cambrian saw a series of mass extinctions during which many shell-dwelling brachiopods and other animals went extinct. The trilobites also suffered heavy losses.

First, organisms may not have sequestered ... Others propose that an extinction of life just before the Cambrian opened up ecological roles, or "adaptive space," that the new forms exploited.

Still, they became extinct more than 10,000 years ... shallow seas about 505 million years ago during the Cambrian period, hunting small organisms. The unusual anatomy that it evolved to have ...

In the case of mammals, the best-studied group of animals, the fossil record indicates that the “background” rate of extinction, the one that prevailed before humans entered the picture ...