DRAMA IN THE PALEOZOIC: A STRUGGLE FOR SURVIVAL

The discovery of two new reptilian trackways from western Indiana provides new evidence into the feeding behavior of early Pennsylvanian tetrapods. The early Pennsylvanian (Morrowan-Atokan) trackway specimen is from the Mansfield formation along the eastern margin of the Illinois Basin, at the Crane (NSWC). Sedimentological study of the locality suggests a coastal tidal flat deposit of well-sorted laminated siltstones. This specimen preserves the trackways of two small individuals traveling together along a non-linear path. The trackway of the larger individual (5.5 cm) is twice the width of the smaller individual and preserves a taildrag. The entire trackway is 129 cm long. The animals appear to have been moving rapidly from the scuffed and attenuated nature of the prints. Although preservation of individual prints is poor, making ichnological identification impossible, enough consecutive printmarks have been preserved to study the trackway. Claw marks, extended rapid movement and the tight curving pattern of the trackway suggest that the track makers were reptilian.

The trackway from Crane provides new insight into behavioral aspects of early terrestrial vertebrates. The scuffed and attenuated prints continue for the entire length of the trackway indicating that the two animals could move quickly for extended distances. The trackmakers also made two tight turns of nearly 180 degrees each over a distance of approximately 0.6 m. These trackway characteristics suggest that some Pennsylvanian tetrapods may have been active, agile land predators. Termination of the smaller footprints suggests the prey was overtaken by its pursuer and eaten. A resting trace at the end of the trackway was made by the larger animal after it captured its prey and stopped to swallow and digest it. The lack of the larger footprints past the resting trace may be due to desiccation and hardening of the substrate as the larger trackmaker rested to bask during digestion as most reptiles are required to do. Reptilian trackways are rare during this time, adding further importance to the track locality.