COMPLEX BURROWING BEHAVIORS ACROSS THE PRECAMBRIAN–CAMBRIAN BOUNDARY IN THE LOWER WOOD CANYON AND DEEP SPRING FORMATIONS

The base of the Cambrian Period is recognized for, among other ecological advances, the onset of complex trace making behaviors that are indicative of bilaterian-grade trace-makers. However, recent trace fossil discoveries from late Ediacaran strata indicate that the proliferation of complex behaviors was already underway before the appearance of the biostratigraphic marker for the base of the Cambrian, Treptichnus pedum, reflected in the fossil record by intricate systematic mining and active metazoan feeding traces. Complex burrowing behaviors are observed in the Wood Canyon Formation strata at Chicago Pass and Boundary Canyon, California, above and below the Precambrian–Cambrian boundary. Multiple morphologically distinct treptichnid traces occur immediately above the Precambrian–Cambrian boundary, and Lamonte trevallis, a complex mat-targeted feeding trace, is present below, within, and above the boundary interval. The presence of Lamonte trevallis indicates burgeoning complexity in shallow marine ecosystems during the late Ediacaran of the western U.S., and provides evidence that advanced feeding behaviors were already at play before the appearance of treptichnids at the base of the Cambrian. These behaviors were geographically widespread and in varied environments, with occurrences of Lamonte trevallis from the Ancient Bristlecone section of the Deep Spring Formation, the Dengying Formation in South China, and the Nama Group in Namibia. The cosmopolitan occurrence of this complex trace, as well as the appearance of other complex Ediacaran-aged traces (e.g.: treptichnid-like behaviors and the undermat mining trace, Plagiogmus) provide evidence for Cambrian-like bilaterian complexity occurring in the latest Proterozoic. The trace fossil assemblages within the Wood Canyon Formation (and the nearby Deep Spring Formation) provide a snapshot of these early bilaterian ecosystems that can be associated with the exceptionally preserved ‘Wormworld’ tubicolous fossil-dominated sections in eastern California and western Nevada.