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Old September 26th, 2014 #34
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Enigmatic fossils could be oldest known animals



This unusual, multicellular fossil looks very different from anything alive today.


Early life Scientists have discovered some of the oldest multicellular organisms - and possibly the world's first animals - in 600 million year old Ediacaran fossils from China.

A detailed examination of the unusual, small, spheroidal fossilised organisms concludes that they could be the ancient precursors to animals, or a type of multicellular algae.

Reported in the journal Nature, the research is offering scientists fresh insights into the early evolution of complex multicellular organisms.

"Our work shows evidence that this organism developed multiple kinds of cells 600 million years ago," says one of the study's authors, Professor Shuhai Xiao from Virginia Tech.

"This is an important discovery for cell differentiation, and a critical step towards multicellular life."

The fossils provide evidence that multicellularity appeared nearly 60 million years before the Cambrian Explosion, when most major animal phyla suddenly appeared in the fossil record.

Multicellular organisms have common characteristics such as cell differentiation, where specialist cells develop to perform specific tasks. Other characteristics include cell-to-cell adhesion, communication between cells, and programmed cell death.

"One of the more important types of cellular differentiation is the separation of reproductive cells from non-reproductive cells, and we believe we have also found evidence for this," says Xiao.

The new findings are based on exquisitely preserved three dimensional multicellular fossils discovered in calcium phosphate rocks in the Ediacaran Doushantuo Formation in central Guizhou Province of South China.

"Six hundred million years ago this region was probably a warm shallow sea," says Xiao.

"Phosphates precipitated out of water in the sediment and replicated the fossils before the organisms degraded."

The Ediacaran Period dates from the end of the global Marinoan glaciation some 635 million years ago, to the Cambrian explosion, 542 million years ago.

Weird and strange

Attempts to characterise fossils from the Ediacaran Doushantuo Formation have been difficult because they look very different from anything alive today.

The fossils analysed in this study are no exception, and may be a group of early animals that have no evolutionary link with today's living animals.

Similar fossils have been previously interpreted as bacteria, fungi, single-celled eukaryotes, green algae, and various types of early animal life (including transitional forms of modern animals, relatives of sponges, sea anemones, or bilaterally symmetrical animals).

The microfossils in this study are probably not bacteria and share similarities with more complex multicellular organisms, say the scientists.

This narrows the possibilities down to transitional forms related to modern animals or an ancient type of multicellular algae.

"We have not proved that these are animal embryos, although it remains one of two possibilities and certainly narrows down the options," says Xiao.

Xiao says further investigation is needed to determine where on the evolutionary tree of life these enigmatic fossils sit.

Questions answered

The discovery is very interesting, says Dr Jim Gehling of the South Australian Museum

"Without this sort of evidence we could never be sure that there were multi-cell creatures in the Ediacaran," says Gehling.

It had previously been speculated that large Ediacaran fossils were just giant single cell creatures with no true internal organs, muscles or nerves, he says.

"It's a very affirmative paper for those of us who believe that the roots to the animal tree of life lie within the Ediacaran period."

Enigmatic fossils could be oldest known animals › News in Science (ABC Science)