MISSISSIPPIAN-AGE SWIMMING TETRAPOD TRACKWAYS FROM THE MAUCH CHUNK FORMATION NEAR TAMAQUA, PENNSYLVANIA

New tracks and trackways, made by a swimming tetrapod, have been recovered from the Mississippian-age middle Mauch Chunk Formation near Tamaqua, Pennsylvania. Mississippian-age tracks and trackways are rare. Any discoveries are important contributions to our understanding of tetrapod distribution and behavior.

The new tracks and trackways are developed near the top of a fining-upward fluvial cycle composed of fine-grained sandstone followed by shale. The base of the cycle is erosive and is overlain by low-angle trough cross bedding. Near the top of the cycle, tracks and trackways are present on two bedding planes associated with preserved linguiod ripple bedforms. One bedding plane preserves a larger dune bedform. Capping the cycle are shales with desiccation cracks, raindrop impressions and impressions of plant stems.

The 70 by 115 cm rock slab is capped by tetrapod tracks that vary in preservation from manus and pes imprints forming trackways to preserved randomly oriented toe picks. The maximum manus digit span is 3.9 cm. Digit IV is the longest and is consistent with a tetrapod interpretation. The longest trackway is 70 cm in length and is composed of 10 tracks. A swimming, rather than stepping pattern, is indicated. The trackways, with full impressions of pes and manus, progress in the same direction, parallel to or slightly oblique to, the paleocurrent indicators. There is also a multitude of randomly oriented toe picks.