First report of Trichophycus from the Lower–Middle Ordovician Meitan Formation of Renhuai area, Guizhou and its significance
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Abstract:
Ichnofossils provide invaluable information in understanding the process of colonization of infauna in the shallow-marine shelf settings during the Great Ordovician Biodiversification Event. The ichnofossil Trichophycus is widely reported from the Cambrian-Ordovician strata. However, only a few studies have been conducted to investigate its temporal and spatial occurrences, evolutionary paths, trace maker identy as well as its ecological features. Here, we report Trichophycus from the Lower-Middle Ordovician Meitan Formation of Renhuai area, Guizhou Province for the first time. These fossils consist of relatively wide, straight to curved, U-shaped burrow segments that are arranged in a protrusive mode. The lower and lateral surfaces of the burrows are characterized by sets of longitudinally arranged, parallel to sub-parallel striae. The burrow lacks lining and the infill shows retrusive spreite structures. These diagnostic characteristics allow an assignation to T. venosus Miller, 1879, which is interpreted as a dwelling/feeding structure constructed by a colony of unknown arthropods, while the trace maker of reported Trichophycus elsewhere may come from various groups, representing behavioral convergence. Trichophycus venosus is a member of the Glossifungites ichnofacies, possibly indicating an initial induration of the sea floor or a short-lived sedimentary hiatus. The ichnofossil Trichophycus may serve as a reliable indicator of firmground in shallow-marine settings. The geological distribution of Trichophycus, a pineer ichnogenus, suggests a diachronic infaunalization in shelf settings between different blocks. Occurrence of Trichophycus in the Meitan Formation represents colonization of the shelf substrate during the Great Ordovician Biodiversification Event on the Yangtze platform, South China.
