Tube construction and life mode of the late Ediacaran tubular fossil Gaojiashania cyclus from the Gaojiashan Lagerst?tte

摘要

Gaojiashania cyclus is a phylogenetically problematic tubular fossil that is only known from the late Ediacaran Gaojiashan Lagerst?tte in southern Shaanxi Province, South China. It is a cm-sized tube that consists of a series of repeated units. Each unit consists of a rigid ring and an originally flexible bucket-shaped tube wall. Each tube maintains a constant diameter. The rigid ring elements typically range from 1 to 2. mm in length, whereas the bucket components are more variable at 0.5-5. mm in length and are ornamented with transverse annuli. Tubes display curving, extension, and constriction at free angles, indicating the original flexibility of the bucket components. The construction of G. cyclus tubes is unique in both fossil and modern tubular organisms, and strikingly differs from that the structure of other known Ediacaran and Cambrian tubular fossils. Integrated morphological, taphonomic, and paleoecological data suggest that G. cyclus may have exhibited a procumbent epibenthic life mode, possibly using the ring structures as anchors to microbially bound muddy substrate. The preserved tubes are interpreted as the original exterior of the organism, as opposed to a life-mode reconstruction as a tube-dweller. The currently available evidence suggests that G. cyclus had non-mineralized or weakly mineralized tubes, and its phylogenetic affinity remains unresolved.