Mississippian-Age Swimming Tetrapod
Trackways from the a Mauch Chunk Formation Near Tamaqua,
R.L., Zellner, G.C., and Simpson,
E.L., 2004 [abs]: Mississippian-Age
the a Mauch Chunk Formation Near Tamaqua, Pennsylvania,
Northeastern Section (39th Annual) and Southeastern Section (53rd
Annual) Joint Meeting (March 25–27, 2004), Abstracts with Programs,
Vol. 36, No. 2, p. 109.
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.