RELATIVE ABUNDANCE OF VERTEBRATE MICROFOSSILS OF THE PIPE CREEK SINKHOLE (LATE NEOGENE, GRANT COUNTY, IN)

The Pipe Creek Sinkhole (PCS) fossil assemblage (Grant County, Indiana) provides a rare glimpse of a late Neogene (Mio-Pliocene) fossil assemblage paleofauna from the interior of eastern North America. Although PCS has yielded a diverse assemblage of medium-sized and large mammals that includes peccaries, camels, a deer-like ungulate, a rhinoceros, a bear, a felid, canids, and a badger, it has produced an even greater abundance of bones of smaller animals, the vertebrate mesofauna and microfauna (bones of which are collectively designated as vertebrate microfossils). Because such small animals potentially provide much information about the environment in which the fossil assemblage accumulated, we investigated the relative abundance of different constituents of the vertebrate microfossil assemblage.

Fossiliferous sediments from the largely unconsolidated sinkhole deposit were wet-screened on site, and the fine fraction of concentrate (retained on a ca. 1-mm mesh screen) later rewashed, after which fossils were picked and sorted. The relative abundance of different categories of small vertebrates was quantified in terms of both the minimum number of individuals (MNI) and the number of identifiable specimens (NISP).

Frog skeletal elements constituted the overwhelming majority of frog bones in the assemblage, followed in decreasing rank order by much smaller abundances of turtles, small mammals, and snakes. The abundance of frogs and turtles is consistent with previous interpretations of the depositional environment of the fossiliferous sediment in a small pond or wetland.