Discoidal fossils from the Ediacaran Wood Canyon formation, Nye County, NV, USA. Parasitic traces in bivalve, potamocorbula amurensis, from the Pearl River Delta, China
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The late Ediacaran lower Wood Canyon Formation in Nye County, Nevada, has shown significant paleontological promise in recent years. Investigations in the Johnnie Range between the Amargosa Desert and Pahrump Valley have revealed a diverse assemblage of pyritized tubicolous fossils, with rare examples showing the preservation of bilaterian-grade throughguts, limited specimens of erniettomorphs, and abundant trace fossils approaching the Cambrian boundary. Here, we report both in-situ and float examples of discoidal structures from sandstones near the Stirling Quartzite-Wood Canyon boundary. These structures range in size from 3.5 to 47.5 mm in diameter and show the quintessential discoidal morphology of Aspidella, with visible concentric rings. Preserved in positive epirelief on the surfaces of desert-varnished coarse quartz sandstone beds, these specimens are generally found as isolated individuals--with the exception of multiple individuals found on smaller blocks of float. Similar discoidal structures have been reported from the region, including Nimbia from the Stirling Quartzite in Nye County, Nevada, and medusozoan strandings from the younger Zabriskie Quartzite in Death Valley, California. Like the other regional examples, the Johnnie discoidal fossils lack associated frond petalodia, which could argue against a holdfast interpretation like Aspidella, though its central boss may suggest otherwise. These discoidal fossils serve to bolster previous reports of the "Ediacara-type" preservation potential of soft-bodied organisms, like Ernietta, from this region.
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M.S.