Taphonomic, Taxonomic, and Behavioral Diversity of Wormworld Fossil Assemblages from Ediacaran Units of the Western United States
O'Neil, Gretchen Rose
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The western United States Deep Spring and Wood Canyon formations contain a variety of late Ediacaran fossils, representing the enigmatic Ediacara biota and a metazoan worm-like fauna. The latter, dubbed “Wormworld”, is comprised of a number of tube-dwelling organisms whose tubes were preserved through pervasive pyritization and carbonaceous compressions, as well as abundant horizontal burrows and grazing traces. One particular site, within Ancient Bristlecone Pine Forest presents a challenge that is not faced at the other localities, as it contains abundant tube-shaped fossils that are lacking in morphological characteristics due to poor preservation. Through investigations into what remains of the fossils and the potential preservational pathways that could produce such fossils, it is possible to use the findings to identify additional tube worm assemblages that may have been overlooked due to the assumed restriction on exceptional preservation based on sedimentology. Alternatively, trace fossils in the area appear to be more readily preserved and abundant, allowing for investigations into trends in frequency and faunal occurrences leading into the Cambrian Explosion. These traces and the trace maker activities are of a particular interest, as they represent the first communities of established bioturbators, which helped oxygenate the seafloor and mix the previously stratified microbial mat-rich substrate. The trace fossils on the surface of the beds represented ichnotaxa that are well-known in Cambrian deposits. However, petrographic thin sectioning revealed an unexpected fossil, Lamonte trevallis, previously only reported from South China. The presence of Lamonte trevallis is evidence for more advanced, complex Cambrian-like feeding behaviors occurring prior to the Precambrian–Cambrian boundary. The diversity of the Ediacaran fossils from the western United States places it among the established Ediacaran exceptional preservation localities and justifies the designation of the Deep Spring/Wood Canyon assemblage as an Ediacaran Lagerstätte.