THE LOWER CARBONIFEROUS NORTH AMERICAN VERTEBRATE PROVINCE: EVIDENCE FROM THE SOUTHERN ILLINOIS BASIN

The Carboniferous terrestrial vertebrate record has greatly improved in the last few decades with the descriptions of new faunas from North America, Europe and Australia. These studies have broadened our understanding of the composition of Lower Carboniferous faunas and indicate previously unknown similarities among North American fresh- to brackish-water faunas, particularly in the Illinois and southern Appalachian Basins. Provinciality within the Euramerican Carboniferous contradicts the hypothesis that during the Lower Carboniferous a single tetrapod province was present across Euramerica.

The Hancock County Locality of north-central Kentucky preserves a typical example of this Lower Carboniferous North American Vertebrate Province. Taxa endemic to this province include the tetrapods Greererpeton and Whatcheeria and the dipnoan Tranodis. These taxa are present in nearly every North American locality examined, but are absent outside the Illinois and Appalachian Basins. The chondrichthyans Ageleodus and Cynopodius are also common components of Mississippian fresh to brackish water faunas in North America, occurring at Hancock County, Delta, IA and Greer, WV. While these taxa occur outside of North America they seem to co-occur only in North America. Additional taxa, such as the acanthodian Gyracanthus, may contribute to provinciality; however, taxonomic uncertainty of this genus prevents firm biogeographic conclusions.

These biogeographic patterns appear consistent across numerous vertebrate clades including tetrapods, dipnoans, and chondrichthyans, and potentially rhizodonts and acanthodians, suggesting a common cause. These patterns may represent either separate dispersal events for each of these clades, or vicariance event involving the isolation of these North American Basins due to uplift of the Acadian Highlands.