The Ediacara Biota of the Wood Canyon formation: Latest Precambrian macrofossils and sedimentary structures from the southern Great Basin

Abstract

Fossils of the Ediacara Biota preserve the oldest indisputable evidence of macroscopic animal life. Although new finds continue to expand the near global distribution of such organisms, relatively abundant and diverse populations of these primarily soft-bodied taxa are known from just a handful of localities. More commonly, reports of late Precambrian fossils consist of comparably lower diversity assemblages (less than ∼10 genera), with a limited number of total specimens (less than ∼1000 reported macrofossils over a broad geographic area). Determining the factors responsible for such differences can help to fully appreciate preserved patterns of Ediacaran biodiversity.

The lower member of the Wood Canyon Formation in the Death Valley region of the southern Great Basin, USA contains fossils of the Ediacara Biota. Here we redescribe previously recovered specimens based on new data from 3D surface scans and report several new finds from this unit. Although this allows the addition of two Ediacara taxa (Pteridinium and Charnia?) to the known diversity in the region, most potential macrofauna consist of amorphous, irregular forms with minimal preserved structures wherein an abiotic origin cannot be ruled out. A combination of factors – including variable taphonomic conditions, difficulty of identification and an original depauperate community – contribute to the observed diversity of this assemblage. Many biases that impact this record are either common (e.g., age, preservation requirements, difficulty of recognition) or comparable (e.g., paleoenvironmental and taphonomic controls) to known occurrences of Ediacara macrofauana. Thus, we argue this fossil record at least partially reflects the original community composition, suggesting that fossils of the lower Wood Canyon record a signal of relatively low diversity of the Ediacara Biota in the lead up to the Ediacaran-Cambrian boundary.