CHONDRICHTHYIANS FROM HANCOCK COUNTY, KENTUCKY (MISSISSIPPIAN: NAMURIAN)

The Hancock County locality preserves a diverse Mississippian (Namurian) fish and tetrapod fauna in four distinct facies. Two chondrichthyans (Ageleodus and Cynopodius) are known from the oxbow-lake facies based upon the recovery of teeth during collection of macro-vertebrate material. Sediments from this facies were collected and sampled to further assess the population of micro-verebrtaes within the facies. Samples were collected by hand from 6 horizontal and 5 vertical transects with each sample consisting of a 25-gallon bucket of sediment. The sediments were then wet-sieved with U.S.A. standard testing sieves (4.00 mm opening to 250 µm opening); fossils were hand-picked from the 4.00 mm and 2.00 mm sieves, and picked from the 1.00 mm, 500 µm, and 250 µm sieves with the aid of a microscope. Two taxa are present in the sieved material: Cynopodius, and an as yet unidentified hybodont. All of the material, except for one Cynopodius tooth and two hybodont fragments, were recovered from the horizon from which most of the macro-vertebrate material was collected. Eleven Cynopodius teeth were recovered during wet screening. The teeth were in similar condition to the previously recovered teeth, most consist of root and crown, though a few are broken with only the root remaining. Individual cusps are missing on numerous specimens. Many small fragments of hybodont spines were recovered during screening. None of the hybodont fragments can be identified to lower taxonomic level. Both Ageleodus and Cynopodius are common components of Mississippian fresh to brackish water faunas in North America. In addition to their presence at Hancock County they co-occur at Delta, IA and Greer, WV. While both of these taxa occur outside of North America, Cynopodius is known from Scotland while Ageleodus has a broad distribution including Australia, Russia, and Great Brittan, they seem to co-occur only in North America. This distribution is similar to what is seen for the tetrapods Whatcheeria and Greererpeton and supports the notion of a distinct vertebrate province in North America during the Mississippian.