USING THE SILURIAN REEF ONLINE DATABASE TO COMPARE BIODIVERSITY BETWEEN FOSSIL REEF LOCALITIES IN ILLINOIS

The Field Museum (FMNH) and the Milwaukee Public Museum (MPM) are nearing completion on a 3 year IMLS project to digitize Silurian fossils of the Midwest. The FMNH fossil invertebrate collection is arranged systematically, while the MPM collection is arranged geographically. By digitizing and combining the data into one dataset, it is hoped that researchers will have better access to specimens in both collections and be able to use these collections to answer questions that were previously not possible due to the physical storage of the collections.

For example, a researcher examining the systematics of Silurian Monomerella brachiopods recently examined 37 specimen lots in the FMNH collection; as a result of the IMLS digitization project, we were able to locate an additional 49 specimen lots of Monomerellaat the MPM.

Watkins (1997) published on the biodiversity of Silurian reefs using Wisconsin localities from the MPM collection, but specimens at the FMNH were not included. Using our database we compared selective collections from Thornton and Bridgeport, Illinois from the MPM and FMNH. This revealed similar compositions between trilobites, brachiopods, bryozoans and corals. However, crinoids represent 2 to 4 times as many specimen lots in the MPM collections, while mollusks have twice as many lots in the FMNH collections. These selective collections differ significantly from Watkins brachiopod-dominated, nonselective collections and represent biases in collecting. Using these same collections to examine biodiversity reveals 165 species from 465 specimen lots in the FMNH Bridgeport collection and 88 species from 487 lots from Thornton. Plotting these against Watkins’s figure 7 rarefaction curves shows that both are higher than any other Silurian reef plot. In comparison, the MPM collection from Bridgeport yields 46 species from 137 lots and the Thornton collection yields 49 species from 313 lots. These differences could be from collection bias, inconsistent identifications, or differences in biodiversity and need further investigation.

This preliminary inspection of the raw data from the Silurian reef database, while not corrected for collecting biases, specimen counts, and identifications does present some interesting leads for further research into Silurian reef variation and biodiversity in Illinois.