AMPHIBIANS AND REPTILES AS PREDICTORS OF THE PALEOENVIRONMENT

The Pipe Creek Sinkhole (PCS) is a 5 million year old fossil site in Grant County, IN that was the first deposit of its age ever discovered in the interior of the eastern half of North America. Seventeen exant taxa of amphibians and reptiles have been recovered from PCS. To reconstruct the paleoenvironment I compared the fossil herp assemblage from PCS to the modern assemblage across the Midwest. The exant species found in the PCS assemblage are typical of species found in a mosaic of open canopy habitats including oak savanna, prairie, wet meadows, and forest edges. Many of these species prefer habitats with loose sandy soils. The aquatic and semi-aquatic herp species suggest that the site had a permanent body of water with ample shallow areas. The presence of Regina sp. also suggests that a rocky stream was in the area. A biogeographical approach using GIS indicates that all 17 exant taxa are currently found together only in southeastern Michigan (near Ann Arbor), whereas only 5 exant taxa are currently found in Grant County, IN. The 30-year meteorological norms of southeastern Michigan are significantly cooler (0.6 C) and drier (10.6 cm) than Grant County. The climate differences are most pronounced for temperature from Feb through September and precipitation from March through July. Together these data suggest that PCS had cooler and drier springs and summers than today, with an open-canopy upland community surrounding a permanent pond and associated wetlands.