EARLY PERMIAN (LEONARDIAN) TETRAPOD FOOTPRINTS FROM LAKE KEMP, NORTH-CENTRAL TEXAS

Tetrapod footprints of Early Permian age are well known in the western United States from Wolfcampian strata, but relatively unstudied in Leonardian rocks. A substantial tetrapod ichnofauna from strata of the Clear Fork Formation at Lake Kemp, Baylor County, Texas, augments the meager North American tetrapod ichnofauna of Leonardian age. The tracks at Lake Kemp occur in the informally-named Craddock dolomite member of the Clear Fork Formation, which is 12-15 m above the local base of the Clear Fork and of early Leonardian age. The track-bearing stratum is a 0.3-m-thick, ripple-laminated and trough-crossbedded, calcareous siltstone that also contains mud cracks, raindrop impressions and some land-plant impressions. We interpret the Craddock dolomite as the feather-edge of a marine transgressive carbonate deposited along an irregular coastline marked by shallow bays or estuaries on the eastern shelf of the Midland basin. At Lake Kemp, the most common tracks are of small temnospondyls, and we assign them to Batrachichnus. The next most common are seymouriamorph tracks assigned to Amphisauropus, which can be assigned to large and small ichnospecies, A. latus Haubold and A. imminutus Haubold. Least common are araeoscelid tracks assigned to Dromopus. A sparse invertebrate ichnofauna consists of arthropod feeding and walking traces assigned to Diplichnites, Helminthopsis, Cochlichnus and ?Oniscoidichnus. The vertebrate (especially amphibian) and invertebrate traces indicate a freshwater setting at the time of track formation. The Lake Kemp tetrapod track assemblage is characteristic of the global Lower Permian tetrapod ichnofauna found in red beds, which is dominated by a handful of ichnogenera that include Batrachichnus, Limnopus, Amphisauropus, Dromopus, Varanopus, Hyloidichnus, Ichniotherium, Dimetropus and Gilmoreichnus. This assemblage is mostly the tracks of temnospondyls, diadectomorphs, seymouriamorphs, procolophonids and pelycosaurs. However, the abundance of Amphisauropus tracks at Lake Kemp is unusual, though it may only reflect the idiosyncracies of track preservation at a specific site.