Scolicia and its producer in shallow-marine deposits of the Miocene Chenque Formation (Patagonia, Argentina): functional morphology and implications for understanding burrowing behavior

Scolicia is one of the most conspicuous trace fossils in lower shoreface deposits of the Miocene Chenque Formation of Patagonia, Argentina. This ichnotaxon consists of horizontal, sinuous or meandering trace fossils with a laminated backfill and two parallel strings located at the base. Abundant body fossils attributed to Brisaster iheringi occur in close association to these trace fossils. The echinoids are very well preserved, and most of the specimens have some areas with their spines attached in life position. In particular, preservation of the subanal tufts of spines, associated to isopores (which are interpreted as being associated to funnel building tube feet), supports the interpretation that these organisms are the producers of Scolicia isp. A shaft connecting the burrow with the sediment-water interface was not observed in vertical sections of the excavations, although on bedding plane surfaces, some small circular tube outlets are recognized. However, the great diversity and abundance of ichnofossils co-occurring in these deposits may preclude adequate identification of vertical structures. These deposits provide an excellent opportunity to integrate trace fossil data, body fossil information and observations from modern analogues in order to perform a morpho-functional analysis of Scolicia.