PALEOBIOGEOGRAPHY OF CINCINNATIAN (LATE ORDOVICIAN) BRACHIOPODS: UTILIZING GEOGRAPHIC INFORMATION SYSTEMS (GIS) TO ANALYZE SPECIES RESPONSE TO ENVIRONMENTAL CHANGE

Examining fine scale temporal and spatial change in the geographic range of individual species provides a framework in which to assess the role of environmental changes on evolution and community structure. In this study, we investigate species level geographic patterns in articulate brachiopods of the Late Ordovician of the Cincinnati Arch region (Maysvillian to Richmondian strata of Ohio, Kentucky, and Indiana) using Geographic Information System (GIS) methods in order to study paleobiogeographic changes.

This study utilizes GIS to manage large amounts of species occurrence data and produce quantitatively constrained geographic range reconstructions that are amenable to statistical analysis. The database of species occurrences includes over 1500 data points with taxonomic, geographic, and stratigraphic information. These data were assembled from museum collections and targeted field collecting. Stratigraphic information is subdivided by formation and includes data from the Fairview through Elkhorn Formations. Geographic ranges were reconstructed individually for each species extant during each stratigraphic interval. This produced a dataset in which fluctuations in species range size and position could be assessed against environmental variables, such as relative sea level.

GIS range reconstruction resulted in over 200 species range maps distributed between fifteen time slices. Statistical analysis reveals changes in the mean size of geographic ranges, per interval, is statistically correlated with regional sea level values of Cuffy (1998) and Holland (1993). In addition, clear patterns of habitat tracking, lateral geographic movement of species in response to movement in preferred environment, are recognized for individual species. Coordinated movement by suites of species may indicate community response to environmental change. These recovered patterns provide additional insight into community structure and evolution with the Cincinnatian brachiopod fauna.