By studying Darwin’s finches and East African cichlids, scientists can get clues that help them understand much older, much bigger adaptive radiations. One of the biggest was the early rise of animals. This period of animal evolution is sometimes nicknamed “the Cambrian explosion.” Unfortunately, that name gives the impression that all the modern groups of animals popped into existence 540 million years ago at the dawn of the Cambrian period. Animals evolved from protozoans, which left fossils over a bil- lion years before the Cambrian. Some 630 million years ago, one group of living animals—sponges—was already leaving behind biomarkers. By 555 million years ago, fossils belonging to some living.
