EARLY CAMBRIAN ZOOPHYCOS AND IMPLICATIONS FOR THE ADVENT OF DEPOSIT FEEDING

Zoophycos-group burrows are prevalent elements of the trace fossil record throughout the majority of the Phanerozoic and are among the most celebrated trace fossils in all of ichnology. Here we report the oldest definitive specimens of Zoophycos from Lower Cambrian strata in the Lower Member of the Wood Canyon Formation in southeastern California. Eight specimens were found approximately 40 m above the Precambrian-Cambrian boundary within the Rusophycus avalonensis trace fossil zone, making them significantly older than any other purported occurrences of Zoophycos. In that these specimens are simple, basically two-dimensional forms occurring with well-defined mud-sand spreite in the absence of a vertical axis and/or any evidence of vertical movement of sediment, the most parsimonious explanation for these specimens is that of a horizontal deposit feeder as has been suggested for other examples of Zoophycos (e.g. Seilacher, 1967, 2007). The discovery of these specimens not only expands the range of Zoophycos nearly to the base of the Cambrian but also reveals the presence of complex burrowing activity and deposit feeding prior to the appearance of the trilobites, considerably earlier than has been suggested for the advent of this feeding style. This type of activity may have had a significant impact on levels of sediment mixing during the Precambrian-Cambrian transition, though the rarity and shallow tier position of these specimens suggests otherwise.