"Looking at fossils can tell you something about the controls on global diversity, but so much of the investigation of the fossil record has looked only at global compilations of fossil species," says Dr. Mark E. Patzkowsky, associate professor of geosciences. "Recently, a few studies have shown that if you look at diversity locally, it is not necessarily mimicking global diversity at that time."
Researchers look at three types of diversity: local or alpha diversity, which is diversity at a specific location; regional or gamma diversity, which is diversity in a large area up to continent size; and beta diversity which is the diversity gained as one moves from one area to another.
Patzkowsky and Steven M. Holland, professor of geology, University of Georgia, looked at fossils similar to modern corals, clams, snails and brachiopods from 450 million-year-old fossil beds in the area around Cincinnati, Ohio. These Ordovician fossils show great diversity of sea floor invertebrates.
They made 700 individual collections and counted about 41,000 individual animal fossils. A typical collection area was a half meter piece of exposed ancient sea floor. Fossils were collected from areas that were originally deep sea floor, deep subtidal sea floor, shallow subtidal sea floor and protected lagoon sea floor. The fossils represent six time slices, each of about a million years, however, for this study, they only looked at fossils from the four time slices that contained fossils from deep and shallow subtidal areas.
"We already knew that there was an invasion of species during one of the time slices," says Patzkowsky. "We wanted to see how that invasion affected diversity."