Ancient marine invertebrate diversity less explosive th...( Diversity among the ancestors of suc...)

Diversity among the ancestors of such marine creatures as clams, sand dollars and lobsters showed only a modest rise beginning 144 million years ago with no clear trend afterwards, according to an international team of researchers. This contradicts previous work showing dramatic increases beginning 248 million years ago and may shed light on future diversity.

"Some of the time periods in the past are analogies for what is happening today from global warming," says Jocelyn Sessa, doctoral candidate in geosciences, Penn State. "Understanding what happened with diversity in the past can help us provide some prediction on how modern organisms will fare. If we know where we have been, we know something about where it will go."

Using contemporary statistical methods and the Paleobiology Database, the researchers report, in today's (July 4) issue of Science, a new diversity curve that shows that most of the early spread of invertebrates took place well before the Late Cretaceous, and that the net increase through the period since, is proportionately small relative to the 65 million years that elapsed.

One key to the new curve is the Paleobiology Database, (http://paleodb.org) housed at the National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara. Previous research was based on databases of marine invertebrate fossils that recorded only the first occurrence of an organism and the last occurrence of the organism. There was no information in between for the organism.

"Over 30 years ago, researchers looked at the curve they had and considered that perhaps diversity did not increase at all," says Mark E. Patzkowsky, associate professor of geosciences. "What researchers saw was the diversity curve leveled off for quite some time and then took off exponentially. However, diversity results are strongly controlled by sampling techniques."

The new database allows researchers t
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