THE FISH SWIMMING TRACE UNDICHNA FROM THE MISSISSIPPIAN MAUCH CHUNK FORMATION, EASTERN PENNSYLVANIA

The ichnogenus Undichna is the swimming trace of a fish that usually consists of a series of sinusoidal waves made on soft sediment at the bottom of standing water by the fins of a fish swimming by anguilliform locomotion. We document the first record of Undichna from the middle member of the Mauch Chunk Formation in eastern Pennsylvania, strata of Late Mississippian (Visean) age. The locality is alongside US Highway 81, approximately 4 km northwest of the town of Hazleton, Luzerne County, Pennsylvania.

The Undichna specimens are preserved in convex hyporelief on a fine-grained mudstone. They consist of pairs of well-defined, narrowly-incised, sinusoidal wave lines that are out-of-phase, have a wave length of 16 mm and a wave amplitude of 2 mm. The intertwined, out-of-phase sinusoidal waves justify assignment to the ichnospecies U. britannica Higgs, 1988.

This first record of Undichna from the Mauch Chunk Formation occurs in ephemeral fluvial deposits in association with a diverse invertebrate ichnoassemblage of the Scoyenia ichnofacies and a tetrapod footprint assemblage dominated by the tracks of temnospondyls, including those assigned to the ichnogenus Batrachichnus sp. and Hylopus sp. Indeed, the slabs of rock with the Undichna traces also have undertracks of Batrachichnus and Hylopus. The Mauch Chunk record of Undichna indicates the presence of a small fish with caudal and anal fins that touched the sediment during periods when intermittently subaerial track surfaces were subaqueous.

Our research indicates that these Undichna trails are the oldest reported examples from ephemeral fluvial deposits and the oldest reported specimen from the USA.