New fossil discoveries in China have transported paleontologists across a Great Divide in the history of life on Earth, taking them deep into virtually unexplored time, showing them the earliest known forms of tiny ancestral animals and pointing out where they should be searching next for evidence of the origins of the first such complex life.
Two teams of paleontologists have found the minute but distinct traces of ancient marine animals and embryos exquisitely preserved in phosphate deposits. The specimens are related to sponges, jellyfish and even more advanced species, including apparent forerunners of trilobites, clams and crabs.Under a magnifying glass, the tiny mineralized organisms reveal striking details down to the cellular level, clearly establishing the abundance and diversity of ancestors of today's animals at least 570 million to 580 million years ago. This extends the fossil history of animals back at least 30 million to 40 million years before the Cambrian explosion, the great evolutionary divide when it seemed that complex life suddenly appeared in a burst of anatomical innovation sometimes called the "big bang of biology."
Moreover, the discovery of such early fossil organisms, which are more complex than sponges or jellyfish, leads scientists to suspect that the initial appearance of multicellular animal life must have occurred at a much earlier time. Genetic studies have recently hinted that the first simple forms of animal life may have emerged half a billion years before the Cambrian explosion.
Looking beyond the particulars of the newly discovered fossils, paleontologists now sense an opportunity to look deeper into the early evolution of animal life. They predict that similar phosphate deposits around the world will yield many more Precambrian fossils, which could be as informative about early multicellular life as the famous Burgess Shale, a rock formation in British Columbia. Fossils from the shale have been invaluable for studying the rapid diversification of life's anatomical designs in the Cambrian period.
One of the discovery teams concluded its report with the prediction that phosphate rocks will "provide a potentially inexhaustible resource for understanding the early evolution of animal life."
Andrew H. Knoll, a Harvard University paleontologist and member of the other group, said, "We have really opened up a wonderful new window into ancient life."