TRACE FOSSIL RESEARCH IN THE MISSISSIPPIAN MAUCH CHUNK FORMATION IN EASTERN PENNSYLVANIA

In eastern Pennsylvania, the Mississippian Mauch Chunk Formation is a more than 1-km-thick succession of siliciclastic red beds that yields nonmarine trace fossils. In 1843, Isaac Lea first reported tetrapod footprints from the Mauch Chunk, naming the tracks Sauropus primaevus (later emended to Palaeosauropus primaevus). We have relocated Lea’s type locality of P. primaevus and have collected trace fossils there and other localities in eastern Pennsylvania. Most of these localities are in the informally named “middle member,” now the Indian Run Member of the Mauch Chunk Formation. Deposition of the Indian Run Member was by low sinuosity braided fluvial systems in a semi-arid to arid setting. Invertebrate ichnofossils from the Mauch Chunk Formation are assigned to the ichnotaxa Diplichnites gouldi Type A, Diplopodichnus biformis, Gordia isp., Kouphichnium aspodon, Planolites beverleyensis, Rusophycus carbonarius, Stialla pilosa, Stiaria intermedia and Taenidium barretti. Of these, only Planolites and Taenidium are abundant, representing the Scoyenia ichnofacies. Both the Diplichnites and Scoyenia ichnoguilds are present, so the Mauch Chunk invertebrate ichnoassemblage confirms that the terrestrial invertebrate fauna had fully colonized fluvial environments by Mississippian time. Vertebrate ichnofossils from the Mauch Chunk Formation include an unusually large tetrapod burrow, probably made by an amphibian, diverse fish swimming traces assigned to Undichna brittanica, U. unisulca, U. quina and U. isp., as well as unique temnospondyl body impressions (Temnocorpichnus isaacleai) that support speculation about social (courtship) behavior among some Mississippian amphibians. Tetrapod footprints are abundant in the Indian Run Member and we assign them to Batrachichnus salamandroides, Characichnos isp., Hylopus hardingi, Matthewichnus isp., Palaeosauropus primaevus and Pseudobradypus isp. The limited tetrapod body fossil record of the Mauch Chunk Formation (one temnospondyl species, and two anthracosaurs) does provide an adequate roster of trackmakers for the Mauch Chunk tetrapod footprint assemblage, which is dominated by temnospondyls with rare anthracosaur tracks. This footprint assemblage well represents the Batrachichnus ichnofacies.