Magazine article Science News

Biology's Big Bang Had a Long Fuse: Animals Started Evolving Long before Showing Up as Fossils

Magazine article Science News

Biology's Big Bang Had a Long Fuse: Animals Started Evolving Long before Showing Up as Fossils

Article excerpt

A new effort to date the early history of modern animals finds a lot of evolutionary dawdling.

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The last common ancestor of all living animals probably arose nearly 800 million years ago, a multidisciplinary research team reports in the Nov. 25 Science. From that common ancestry, various animal lineages diverged and evolved on their own paths. Yet the major animal groups living today didn't arise until roughly 200 million years later, in an exuberant burst of forms preserved in fossils during what's called the Cambrian explosion.

"There's a deeper history that's been missing from the fossil record," says study coauthor Kevin Peterson of Dartmouth College. He and his colleagues have been pushing back that date for a last common ancestor, and now, he reports, the analysis has the broadest reach yet. "We show that animals evolved quite a bit before they show up in the fossil record."

This work updates the notion of a long evolutionary lag, when much of the basic biological toolkit was already in place for a later surge of new body forms, says paleontologist and study coauthor Douglas Erwin of the National Museum of Natural History in Washington, D.C., and the Santa Fe Institute.

"The Cambrian explosion is like the industrial revolution," Erwin says. Inventions that would later be important for a major shift in technology--or, in this case, genetic novelties important for evolution--appeared long before they played a role in widespread changes that had a major impact on life.

For understanding animal origins, the new paper "is really worthwhile as it stands back and tries to make sense of the whole picture," says James Valentine of the University of California, Berkeley, who studies animal evolution.

Just what happened with animals during that Cambrian explosion remains one of the more celebrated puzzles in the history of life. Charles Darwin mused over how diverse animal forms appear suddenly (geologically speaking) without much in the way of precursors. Darwin's answer, as Erwin puts it, was that paleontologists just needed to look harder.

More than a century of hard looking has turned up some signs, fossils as well as traces of biological chemistry, of enigmatic animal life before the Cambrian period began about 541 million years ago. …

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