An ethological interpretation of zoophycos based on permian records from South China and Southeastern Australia

Abundant, well-preserved Zoophycos is common in the lower and middle Permian paleotropical neritic limestone of South China and in the middle Permian glaciomarine lithic wackestone of southeastern Australia. Zoophycos from both regions is composed of a marginal tube and a tongue-like spreiten complex, the latter itself consisting of primary lamellae in planar view and backfill structures (dark and light menisci) in cross-sectional view. The Zoophycos tracemaker is interpreted to have periodically collected and fed on the surrounding nutrient-enriched sediments within a shallow depth of the seafloor. The dark menisci may correspond to the burrowing phase, whereas the light menisci may be related to a multiple-behavior phase, including dwelling, feeding, farming, resting, and excreting. Symbiotic microorganisms (e.g., sulphate-reducing bacteria) may have been closely involved with the Zoophycos tracemaker in producing the complex structures of the spreiten, based on the abundant pyrite framboids that were found in the Zoophycos spreiten. We suggest that Zoophycos is not simply a biogenic sedimentary structure formed by the motion of the tracemaker; rather it represents a set of complex and elaborate biogenic structures formed by a succession of life behaviors of the tracemaker along with its symbiotic microorganisms. The complete formative process of Zoophycos is reconstructed and linked to its morphology, based on this interpretation.