A Partially Articulated Cynodont Encased in a Putative Burrow Structure from the Cynognathus Subzone C
Date
2015-10
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Abstract
A sedimentary structure containing a fossilized therapsid, and bioglyphs on the
surface morphology, was found during a field expedition to Cynognathus subzone-C in the
Eastern Cape, South Africa. A combination of surface scanning, petrographic thin sections,
bone mapping and anatomical comparison were used to determine the deposit type and
taxonomic identity of the encased therapsid, and examine the implications for biostratigraphy
and faunal assemblage of the Cynognathus Assemblage Zone. The deposit is hypothesized to
be a portion of a cynodont burrow (burrow margin) that was constructed in fluvial sediment
near a river bank. This is the first account of a burrow in subzone-C. Pattern and
directionality analysis of the bioglyphs suggest that the bioglyphs are scratch marks made by
the burrower during excavation. The scratch marks are mediolaterally narrow, with some
exhibiting indentation marks, indicating that the tracemaker had mediolaterally narrow
unguals at the distal phalanx (claws). Anomodonts and cynodonts were common burrowers
during the Triassic, however comparisons of Thrinaxodon and Lystrosaurus scratch marks to
the bioglyphs on this deposit suggests that the bioglyphs were likely constructed by a
cynodont as anomodont unguals are laterally wider, and are unable to create mediolaterally
narrow markings. The tracemaker is hypothesized to be closely related to Thrinaxodon based
on scratch mark comparison. However, bioglyph published literature is limited, and therefore
the tracemaker cannot be identified. The therapsid was identified as Diademodon based on
cranial and dental morphology. There is limited published literature on Diademodon
constructing and/or exploiting burrows, however the taphonomy suggests that the
Diademodon was near the entrance or in the tunnel of burrow nearing/during death. This is
the first account of Diademodon encased in a burrow.
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Keywords
cynodonts, Triassic, Karoo, ichnology