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Study Clarifies Evolutionary History Of Early Complex Single-Celled Life

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Tysons Corner VA - Mar 27, 2004
A billion years ago (the Neoproterozoic age), complex single-celled organisms, the acritarchs, began to develop, grow, and thrive. Almost a billion years later, the study of the evolutionary history of acritarchs began to bog down amid inconsistencies in the reporting of the diversity of species.

Now, a Virginia Tech graduate student has devised a new way to study the ebb and flow of life in the Neoproterozoic and Early Cambrian ages, a period that includes two mass extinctions. John Warren Huntley of Asheville, N.C., a PhD. Student in geosciences, reported on his strategy and results at the joint meeting of the Northeastern and Southeastern Sections of the Geological Society of America, held March 25-27 in Tysons Corner, Va.

"The evolutionary history of acritarchs reported in the literature has been based on the number of species," explains Huntley. "But there have been many workers collecting information and there is variation among these researchers on what is considered a species. This variation among workers could alter our understanding of what actually happened."

The strategy of a group of geoscientists at Virginia Tech is to use the quantitative data reported in the scientific literature to look at size and morphological complexity of specimens collected.

So far, they have examined acritarch data spanning more than 700 million years from 1270-million-year-old rocks deposited long before Neoproterozoic ice ages, to Early Cambrian successions rocks deposited during the explosive evolution of early animals.

"Our preliminary results seem to confirm previous anecdotal evidence," says Huntley. "We're finding that complexity increases through time, which is to be expected." However, complexity leveled off. "It appears that morphological complexity may have remained steady at high values, even when species diversity was fluctuating greatly," Huntley says.

As to size, there was a steady increase in size for at least 500 million years, until the Ediacaran extinction, after which acritarchs remained very small compared to their pre-Ediacaran extinction size. "There had been anecdotal observations of the size change, which we have now quantified," Huntley says.

Huntley presented the paper, "Secular patterns in morphological disparity and body size of acritarchs through the Neoproterozoic and early Cambrian" (47-2) Friday, March 26.

The trio began their study of acritarchs last October. "It is interesting to use novel techniques to study early life and this is a good opportunity to increase my knowledge in this important area, " says Huntley, who has been studying mollusk evolution.

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Christopher Chyba is the principal investigator for The SETI Institute lead team of the NASA Astrobiology Institute. Chyba formerly headed the SETI Institute's Center for the Study of Life in the Universe. His NAI team is pursuing a wide range of research activities, looking at both life's beginnings on Earth and the possibility of life on other worlds.



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