A NEW OCCURRENCE OF THE REPTILE TRACKWAY NOTALACERTA MISSOURIENSIS FROM WESTERN INDIANA

The discovery of a reptile trackway from the early Pennsylvanian in western Indiana has provided new insight into the distribution of primitive reptiles. 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 have been recovered from this locality of several taxa of tetrapods suggesting a diverse ecosystem existed here. 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 inhabited by a number of types of primitive tetrapods ranging from small to medium size. Our set of prints are similar to those of Notalacerta missouriensis from the Pennsylvanian of Missouri and Kentucky, yet the new trackway lacks the tail drag impression typical of N. missouriensis. The new tracks also have complete and rounded sole impressions while N. missouriensis typically lacks or has a triangular sole impression. However, aside from these extramorphological variations, the new tracks have similar proportions to N. missouriensis and show other similar characteristics such as lacertiod digits and digit four being the longest, suggesting the trackway should be assigned to N. missouriensis. This trackway represents the earliest evidence of reptiles in the Illinois Basin, and one of the earliest occurrences of reptiles in North America. The recovery of this trace provides insight into the early diversification and distribution of reptiles shortly after their appearance in the early Pennsylvanian. The new trackway implies that reptiles were present in the Illinois Basin during the early Pennsylvanian, suggesting that the distribution of primitive reptiles was much broader than previously believed.