Newly announced discovery sheds light on most fecund era in Earth's history.
In what may rank as one of the most important fossil discoveries in decades, researchers have found exquisitely preserved remains of tiny creatures, opening a long-hidden window on early animal life.
Ranging from 570 million to 580 million years old, the microscopic animal fossils reveal their secrets in surprising detail - down to the level of individual cells. This is raising hopes that paleontologists will be able to document, at the most basic biological levels, key stages in the evolution of animals as they shifted from soft-bodied, microscopic forms to those visible to the naked eye.
In particular, researchers are keenly interested in finding fossil evidence for the evolutionary fuse that led to the Cambrian explosion - a burst in the diversity of life unmatched in Earth's history.
The explosion, which began roughly 550 million years ago and lasted a few tens of millions of years, gave rise to virtually every body plan seen in the animal kingdom today.
"This is going to trigger a flurry of activity," says Sean Carroll, a developmental biologist at the Howard Hughes Medical Institute and the University of Wisconsin at Madison, referring to the latest discoveries. "There is tremendous interest in the Cambrian explosion, when there was a huge increase in the size and diversity of animals. Before the Cambrian, we do not see that level of innovation," he says. "People thought that some of it was there in small, poorly preserved animals, or maybe it wasn't there at all."
Two groups reported the fossil finds independently this week.
One research team, based in Taiwan and the People's Republic of China, looked at phosphate deposits in southern China and found highly detailed remains of early sponges. They are reporting their findings in tomorrow's issue of the journal Science.
Meanwhile, Shuhai Xiao and Andrew Knoll of Harvard University, in Cambridge, Mass., and Yun Zhang of Beijing University analyzed microfossils taken from a phosphate mine also in southern China. They describe their work in today's issue of the journal Nature.
Combing the phosphate deposits, part of a 57-square-kilometer (22-square-mile) formation known as the Doushantuo phosphorites, they uncovered several specimens of multicelled algae, whose structure and reproductive features also appear in modern marine algae. They also discovered tiny globules that, after Shuhai Xiao's detective work, appear to be embryos from the same kind of organism. The embryos show different stages of division.