PROPOSED SKELETAL REPAIR AND ACCRETIONARY GROWTH OF AN ENIGMATIC EDIACARAN ORGANISM, ALBEMARLE GROUP, NORTH CAROLINA

A specimen of an enigmatic Ediacaran taxon, previously undescribed in the Carolina Terrane, was discovered in float material of the Floyd Church Fm. near Albemarle, NC. The fossil is preserved as a partial external mold in meta-siltstone, found at a locality in which Pteridinium was previously reported. The 32-mm-long and 16-mm-wide specimen is composed of a series of annulations of multiple size orders, and appears terminated at both ends (or the organism was disarticulated prior to emplacement and preservation). Small annulations average 128μm in width (n=106) and comprise larger annulations (mean=2.16mm, n=9). The topography of the specimen and presumed deformation (but not fracturing) perpendicular to the annulations and parallel to the long axis suggest a pre-mortem rounded or cylindrical morphology that underwent post-mortem compaction. The organism is interpreted to have grown by episodic accretion of a non- or weakly-biomineralized skeleton, exhibiting gross morphological similarities to tubular organisms from the Gaojiashan and Nama biotas. Also similar to Gaojiashan tubes, this specimen shows a strong taphonomic association with pyrite (or later iron oxide) along the outer tube-wall edges. A trapezoidal fracture, 4.3 mm wide and 0.9 mm deep, crosscuts annulations, opens toward the presumed anterior, and was filled by additional annulated material. As the low energy environment indicated by silt deposition argues against non-biotic environmentally-induced structural damage, it appears that this damage was sustained and repaired while the organism was still alive, and was perhaps predatory in nature, though the phylogenetic nature of such a predator is unknown. If the repair scar was indeed predator-induced, these would be the oldest known examples of durophagous predation and survival of such an attack in the fossil record. This specimen increases the known diversity of Ediacaran organisms in the Albemarle Group by 50%; Pteridinium and Aspidella being previously reported. The Ediacaran strata of the southeast United States have received inadequate attention from paleobiologists and are therefore ripe for discovery of new fossil forms.