Paleoecology of a large Early Cambrian bioturbator

The Lower Cambrian Poleta Formation in the White-Inyo Mountains of eastern California contains well-preserved and laterally extensive exposures of the large looping and meandering trace fossil Taphrhelminthopsis nelsoni n.isp . Such traces are typical features on upper bed surfaces of Lower Cambrian shallow marine sandstones and occur with Ediacaran fossils at other localit ies. Morphologic, sedimentologic and gonio-gram analyses suggest that the i nferred tracemaker was a large soft-bodied echinozoanor mollusc-grade anima l with a volume greater than 14 cm(3) that actively grazed or ingested sedi ment at the sediment-water interface. Although portions of these traces app ear to reflect relatively 'complex' behavior, looping patterns are not peri odic as expected for a systematic foraging strategy. T. nelsoni traces are patchy in distribution and commonly associated with suspect-microbial featu res, suggesting that tracemakers may have been targeting microbial-based or related concentrations of food resources. Such behavioral patterns are typ ical of shallow late Neoproterozoic-early Cambrian settings, and like suspe ct-microbial structures are later restricted to deep marine or stressed set tings.