Endolithic bioerosion traces attributed to boring bryozoans in the Eocene of Antarctica

Abstract

The endolithic bioerosion structures described herein were found on the external surface of right valves of Ostrea antarctica Zinsmeister from the lower section of the Eocene La Meseta Forrnation, on Seymour Island, Antarctica. The traces are referred to Feldmannia cavernosa new ichnogenus and new ichnospecies and are the first evidence of boring bryozoans in the Eocene of Antarctica. This is the first trace fossil attributed to boring bryozoans that furniches evidence of strong substrate specificity. This fact, and because the perforations were made when the oysters were alive, suggests probable symbiotic relationships, which ha ve not be en previously recognized in boring bryozoans. The presence of Feldmannia cavernosa together with the remaining traces of the ichnocoenosis suggest that, reinforcing the sedimentological and stratigraphical evidence, the levels bearing Osirea antarctica represent a flooding surface in the lower section of the La Meseta Formation.