Comparing Biodiversity of Silurian Reefs in Illinois and Wisconsin Using Museum Collections and Unbiased Bulk Samples

Silurian (Wenlock) fossil reefs from the Racine Formation in Illinois measure over 100 meters tall and draping flanks beds extend over a mile. Biodiversity studies of reefs in Southeastern Wisconsin reveal complex, diverse communities with over 191 species. We hypothesized that the larger reefs reflect a more optimal environment and may have had higher diversity than reefs in Wisconsin. We compared diversity between the reefs using, identified fossils from the Field Museum, which were collected in Herscer, Romeo, Thornton, Bridgeport, and Hawthorn. Then we compared the results with those from Watkin’s (1997) counts, collected from Horlick, Ives, Franklin, and Francy quarries. We also collected an unbiased bulk sample from Thornton quarry and compared it to unbiased samples from Wisconsin. We found that the unbiased samples had greater differences than the museum collections when compared. The most variable group are echinoderms, In Watkin’s bulk sample data, Echinoderms ranged from 0-22% of the Fauna, in the ours they accounted for 55% of the fauna. Selected samples also showed large amounts of variation in reef composition. This could be due to museum bias for larger specimens, each locality could represent different reef communities, or because Watkin’s had a larger sample size.