A NEW AMPHIBIAN TRACKWAY FROM THE PENNSYLVANIAN OF INDIANA

The recovery of a complete set of tetrapod tracks from the Early Pennsylvanian of Western Indiana has provided new insight into the diversity of the terrestrial vertebrate fauna of the Illinois Basin during that time. The trackway was found along the banks of Big Pine Creek, Warren County, Indiana on the northeast margin of the Illinois Basin. Cox (1874) originally described Collettosaurus indianaensis from this locality. Recently, numerous other tracks of several taxa of tetrapods have been recovered from this locality suggesting a diverse ecosystem existed there. The tracks are found in thin interbedded shales and sandstones from the Mansfield Formation. Unfortunately none of the recently discovered material has been found in situ. Geology of the site reveals that this was probably a tidally influenced mud flat setting. This is supported by the presence of desiccation cracks and rain drop structures. Due to digit, palm and pace angulation measurements, it is presumed that the track maker was a small anthracosaur amphibian. Of the track specimens that have been collected from this locality, the newest trackway is the longest and best preserved consisting of six consecutive, complete manus-pes sets. Trackway measurements and features, when compared to other known Paleozoic tetrapod tracks suggests that this is a new ichnospecies of Cincosaurus, whose ichnogenus is also known from Alabama and Georgia. The new trackway expands the terrestrial vertebrate faunal list for this locality. It also expands that faunal list for the Illinois Basin, for which terrestrial vertebrates are extremely scarce during that time. The Big Pine Creek track locality is important for its apparent diversity of tetrapods, compared to most other Carboniferous track localities in North America, which have generally produced lower diversity faunas, suggesting that tetrapod faunas were more diverse during that time than previously believed.