The First Reported Arthropod Trackways from
the Pennsylvanian Llewellyn Formation: Bear Valley Strip Mine,
Shamokin, PA
Smith, Casey J., Simpson,
Edward L., and Fillmore, David, 2009, The First Reported Arthropod
Trackways from the Pennsylvanian Llewellyn Formation: Bear Valley Strip
Mine, Shamokin, PA [abs]: Geological Society of America Northeastern
Section - 44th Annual Meeting (Portland, Maine 22–24 March 2009).
The
Pennsylvania
Anthracite region is noted for producing some of the
world's most spectacular paleobotany specimens; the lesser known are
the insect body fossils. The newly discovered trace fossil from
the Llewellyn Formation is the first reported arthropod trackway.
The trackways—Diplichnites gouldi Type A—were discovered in the lower
Pennsylvanian Llewellyn Formation between the Middle split (No.
8½) and Top split (No. 9) of the Mammoth coal zone.
Analysis of the invertebrate ichnofauna revealed undertracks developed
on a shale/siltstone to "clean" subgraywacke. The trackway displays
multiple morphologies. Appendage imprints are sharply defined and
are best interpreted as locomotion traces. The trackways
exhibit the required digit appendage pattern of arthropods including:
1) curvatures equating to angular changes in locomotion, 2)
identifiable internal and external widths repeated in a symmetrically
staggered alternating pattern, 3) measurable stride distances
(repeatable digit distance), and 4) appendage morphologies of digit
traces—circular, ellipsoidal, elongated, and comma internal digits—in
an oblique V-shaped orientation to the angle of mid-line
symmetry. This new trace fossil suggests the possible existence
of a diverse inchnofossil assemblage that could lead to a greater
insight into the potentially complex ecosystem developed among the
Pennsylvanian coal swamps.
