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Eight-armed animal preceded dinosaurs

Scientists have discovered what they believe is an eight-armed creature, which colonised a large section of the world's oceans over 300 million years before the first dinosaurs emerged.

The findings represent the first comparable animal fossils from the Ediacaran Period, 635 to 541 million years ago, which appear in two drastically different preservation environments - black shale of South China and quartz rock of South Australia.

"According to palaeogeographic reconstructions, South China and South Australia were close to each other at the time, belonging to a supercontinent called Gondwana," says lead author Dr Maoyan Zhu.

Zhu, a scientist at the Nanjing Institute of Geology and Paleontology at the Chinese Academy of Sciences, first helped to make the China-Australia connection two years ago during a Beijing conference. He showed a photo of the unusual eight-armed creature, called Eoandromeda octobrachiata, to co-author Dr James Gehling of the South Australia Museum.

"He was so surprised and immediately opened his laptop and showed me images of new fossils uncovered from a new locality at the Flinders Ranges of South Australia," says Zhu. "We wondered if these were the same fossils."

Zhu, Gehling and their colleagues collected eight compressions of the animals from the Doushantuo Formation at Wenghui, China.

They then traveled to Flinders Ranges, Australia, and collected seven specimens, leaving 31 others on two excavated and reassembled beds.

The findings are published in the November issue of Geology.

There is no question the creature, believed to represent one type of animal, had a lot of arms.

Simple and symmetrical

The eight arms are clearly preserved in our specimens," says Zhu, adding that the arms were tubular and in close contact with each other, but not joined.

He and his colleagues believe the animal was a soft-bodied, dome-shaped organism that lived on seabeds and fed by absorbing dissolved nutrients from the ambient environment.

Before the latest fossils were found, some researchers identified the creatures as lichens or fungus-like organisms, but Zhu and his team suspect that at least some Ediacara fossils represent now-extinct diploblastic animals, or creatures that possess only two cellular layers separated by a jelly-type substance.

"Diploblastic animals are common creatures on present day earth," he said, mentioning that jellyfish, corals and sea anemones belong to the group.

"These animals (display) radial symmetry but lack complex organs, as shown by E. octobrachiata," he adds.

The multi-armed creature, and several other early life forms, went extinct around 542 million years ago, which Zhu says, "left empty niches for the subsequent Cambrian explosion of complex animals."

Representatives of nearly all existent animals emerged at this time, when a rapid increase in oxygen made respiration and metabolism possible.

Bridging the gap

In a separate paper, Professor Shuhai Xiao, a researcher in the Department of Geosciences at the Virginia Polytechnic Institute and State University, and colleague Dr Marc Laflamme provide an overview of Ediacara fossils.

In the paper, which has been accepted for publication in the journal Trends in Ecology & Evolution, Xiao and Laflamme agree that, "Ediacara biota bridges the cryptic evolution of multicellular life in the early Ediacaran and the extraordinary radiation of animals in the Cambrian period."

In addition to the eight-armed creature, they describe other early living things that looked like leaves, shells, stars and something almost akin to a peace symbol.

Xiao and Laflamme hope that as the Ediacara fossil database grows ever larger, more mysteries about these very early organisms will be solved.