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Scientists from China and the US have moved one step closer to deciphering the developmental biology of the oldest animals on earth after completing their research on 600-million-year-old embryo fossils from southwest China's Guizhou Province.

The paleontologists' study has revealed how the ancient animal embryos developed into mature adult forms, according to the front-page article published in the February issue of Geology, the journal of the Geological Society of America.

The scientists studied some 80 pieces of fossilized embryos in the act of cleaving, said Yuan Xunlai, a member of the Sino-US embryos research team that carried out the study.

Yuan, from the Chinese Academy of Sciences, told Xinhua News Agency on Tuesday that each embryo is about the size of a grain of sand, and is comprised of two to nearly 1,000 cells.

Each embryo cloaked itself inside an envelope patterned with tiny holes similar to stitching on a baseball; the envelope was used to transport, store, or metabolize molecules, he said.

Scientists used X-ray computed tomography and other scanning equipment to peel off the envelopes and discovered that the embryo cells were dividing and unfurling.

"Previously we had discovered that some cells were clustered together, but they showed no signs of dividing," Yuan said.

About a decade ago, paleontologists from the US and China discovered thousands of 600-million-year-old embryo microfossils in Doushantuo Formation, a fossil deposit near Weng'an, Guizhou Province.

Later they unearthed fossils of a tubular coral-like animal, which they named Megasphaera ornata for its appearance, and found them to be the adult forms of the embryos.

The new fossils could provide the missing link between the egg and adult of one of Earth's earliest animals, said Zhou Chuanming, a researcher with the Nanjing Institute of Geology and Paleontology.

Zhou said the discovery could point toward how ancient animals developed and reveal the unending evolvement journey of Earth's life forms.

But scientists added that they must see other intermediary stages in order to understand the complete developmental journey of the ancient animals.

(Xinhua News Agency February 7, 2007)