THE HANCOCK COUNTY TETRAPOD FAUNA: IMPLICATIONS FOR THE ORIGIN OF TERRESTRIALITY

Early tetrapods are first recorded from the Frasnian of eastern Greenland and their record extends from the Late Devonian into the Early Carboniferous. The early record of tetrapods in the Devonian and Carboniferous contains significant gaps; the most notable is a 30 million year period at the base of the Mississippian that is represented by only two localities. In addition to temporal biases in the early tetrapod fossil record both geographic and environmental biases exist. A majority of Early Mississippian localities are located in Great Britain and North America and represent deposition in pond or estuarine paleoenvironments. A new Early Carboniferous tetrapod locality in Hancock County, KY preserves a number of tetrapod fossils from a fully terrestrial environment. A rich tetrapod fauna has been collected from the Buffalo Wallow Formation (Mississippian, Chesterian). The locality preserves a gray to black shale interpreted as a fresh- to brackish-water oxbow lake deposit. In addition many fossils are derived from a 10 cm thick horizon within a tan to buff paleosol lateral to the shales. Three distinct vertebrate taxa have been reconized from the horizon: an anthracosaur, a temnospondyl, and a previously unknown form. The anthracosaur is represented by numerous embolomerous vertebrae, pectoral and pelvic material, as well as limb elements. Based upon the number and sizes of known limb elements at least two individuals are represented. Temnospondyl material includes pelvic material and ertebrae. The third taxon is represented by numerous dorsal vertebrae possessing morphologic features normally attributed to stratigraphically younger groups. Fusion of the centra to the neural arch and the orientation of the zygopophyses are characters associated with a higher degree of terrestriality than is previously assigned to Mississippian forms.