Thursday, December 10, 2009

Spectacular Fossils Record Early Riot of Creation.(Science Desk).

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NEW fossil discoveries in China, hailed as among the most spectacular in this century, show that the dramatic transformation of life from primeval single-cell organisms to the complex multicellular precursors of modern fauna was more sudden, swift and widespread than scientists had thought.

From cream-colored sediments of what was a sea floor 570 million years ago, paleontologists have extracted specimens of 70 species of trilobites, worms, sponges and various ancestors of crustaceans, spiders and insects. They are not only the oldest such fossils ever found but, more remarkably, their soft-body parts as well as skeletal and shell remains are unusually well-preserved.

The fossils give scientists their first glimpse of the strange creatures that populated the seas in the early stage of what is known as the Cambrian explosion. The Cambrian geological period, from 570 million to 500 million years ago, saw the appearance of increasingly complex marine animals in a riot of shapes and anatomical designs anticipating much of life as it is today.

Scientists are not sure what touched off this riotous proliferation of more advanced life forms after three billion years in which life never rose above the rudimentary level of bacteria, algae and some primitive worms. Life did not begin appearing on land until after the Cambrian period.

Dr. Jan Bergstrom, a paleontologist at the Swedish Museum of Natural History in Stockholm who analyzed the Chinese fossils, said they suggested that the Cambrian transition was "a revolution perhaps more than evolution."

Most of the Chinese fossils, Dr. Bergstrom said, resemble species identified in the Burgess Shale, the 530-million-year-old fossil beds in the Canadian Rockies that have been the main source of knowledge of that crucial period.

The similarities are the basis for the conclusion that the diversification and proliferation of new life forms must have occurred rapidly at the outset of the Cambrian period.

"Evolution of these creatures seems to have been a sudden and widespread phenomenon," Dr. Bergstrom and colleagues wrote in the current issue of Research and Exploration, a scholarly journal of the National Geographic Society.

The Chinese fossils were discovered in 1984 at Chengjiang, in the southern province of Yunnan, by Dr. Hou Xianguang of the Nanjing Institute of Geology and Paleontology. Dr. Chen Junyuan, also of the institute, is continuing excavations at the site.

But the first descriptions of the fossils were largely confined to Chinese publications and received little attention from scientists elsewhere. This is changing, though, with the new analysis led by Dr. Bergstrom, an authority on trilobites, ubiquitous creatures of that period that have long been extinct. His collaborators include Maurits Lindstrom, a geologist at Stockholm University, and Dr. Chen and Dr. Hou.

As the full import of the discovery is recognized, scientists are describing the fossils as "genesis material" and one of the most exciting finds since the ancient marine life in the Burgess Shale was first explored in 1909. "All eyes are on Stockholm," said Gregory D. Edgecombe, a paleontologist at the American Museum of Natural History in New York. He said the preservation of the Chinese fossils was even better than in the Burgess material.

Dr. Andrew Knoll, a Harvard University expert on early life, said: "We knew from the Burgess that there was a tremendous diversity of life in the Cambrian. Most of everything that was going to happen, all the ways of making invertebrate animals, had already happened by the mid-Cambrian. Now, it seems the new life forms were invented within the first few million years of the Cambrian."

A few million years is but a blink of the eye in the geological and evolutionary time scale. And Dr. Bergstrom said it was quite possible that at this time "you could have the formation of an entirely new type of animal within thousands of years."

Calling the Chinese fossils "fascinating and important," Dr. Steven M. Stanley, a paleontologist at Case Western Reserve University in Cleveland and author of "The New Evolutionary Timetable," said he was not surprised that they resembled the Burgess specimens. "We've known there had to be rapid diversification of life at that time," he said. Unusually Well Preserved

The Chengjiang fauna lived on the sea bottom or just below or above it, along a broad continental shelf beneath fairly shallow waters. Even some of the animals without hard skeletons or shells were preserved intact, which is extremely rare. Skeletonized animals make up more than 99 percent of the fossil record.

Dr. Bergstrom could only speculate on the conditions leading to such deposits of ancient invertebrate life.

"A violent storm probably stirred up the sea bottom and the mud settled over a large area, cutting off the animals' oxygen and preserving them," he said. "You can go 30 miles in one direction and 12 in another and still come up with fossils."

Despite their great age, a majority of the fossil species at Chengjiang belong to animal groups that still exist, including sponges, certain worms, bivalves of the brachiopod group and arthropods. Indeed, arthropods dominate the fossil bed with at least 30 species. These include three species of trilobites and several creatures with long tails that looked like shrimp. The arthropods' descendants are crustaceans, insects and spiders, and the family resemblances can be seen that far back.

For example, the Alalcomenaeus, also found in the Burgess Shale, has distinctive large appendages on its head. Similarly, Jianfengia looks like a small shrimp, and though it lacks typical antennas, it does have "great appendages" on the head.

The second most common group consists of sponges, most of which bear a striking similarity to the Burgess Shale sponge fauna. Other creatures were distantly related to the jellyfish, some flat and others shaped like a corkscrew or spindle. The tallest stood almost two feet above the sea floor. One carried a large disk with concentric air chambers divided into numerous partitions.

Dr. Bergstrom's team is not sure what to make of some of the specimens. The largest animal found, a two-foot-long predator, had stout, segmented arms and a round mouth encircled with cutting "knives." One puzzle is whether this is a type of worm or an arthropod.

Other fascinating specimens include worms with a proboscis armed with spines and a long creature that looks like a worm with a shelly hat. Worm With 'Kneecaps'

"The real shocker for me is the worm that looks like it has kneecaps," said Dr. Ellis L. Yochelson, a paleontologist at the Smithsonian Institution. He was referring to an animal known as Microdictyon.

In earlier discoveries, scientists had noticed the tiny shell-like plates that Dr. Yochelson likened to kneecaps. But they had no way of knowing or suspecting that the plates would sit on a wormlike animal.

In their report, Dr. Bergstrom and his colleagues said these plates were situated in 10 pairs along the body of the Microdictyon. From the area of each pair of plates extended a pair of very long legs or tentacles. "The body design," they said, "seems completely unlikely, but it must once have been functional."

Dr. Yochelson said: "The record of extremely complicated organisms has been pushed back significantly by this find. And it says there was a much shorter interval than expected for the evolution of multicellular animals with hard parts."


Photos: Paleontologists have discovered 70 fossil species in sediment of what was a sea floor 570 million years ago. This fossil appendage of early trilobite-like arthropod was found in the Cambrian layer in China. (Uno Samuelsson/National Geographic) (pg. C1); Fossil arthropod called Jianfengia was found in the Cambrian sedimentary layer at Chengjiang, China. (Uno Samuelsson/National Geographic) (pg. C10) Map: Map of China showing location of Chengjiang. (pg. C10)

Source Citation
Wilford, John Noble. "Spectacular Fossils Record Early Riot of Creation.(Science Desk)." New York Times 23 Apr. 1991. Academic OneFile. Web. 10 Dec. 2009. .

Gale Document Number:A175188355

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