Borers and encrusters as giveaways to the presence of hermit crabs in Antarctic Eocene gastropods

PARRAS, ANA; CASADIO, SILVIO; GRIFFIN, MIGUEL; MARENSSI, SERGIO; SANTILLANA, SERGIO

Puerto Madryn

Otro; Reunión Anual de la Asociación Paleontológica Argentina; 2005

CEMPAT-APA

Eocene rocks from Seymour Island, at the northern tip of the Antarctic Peninsula, contain a record of remarkable molluscan shell concentrations representing ecosystems with no Recent parallels, as they developed in a relatively warm (c. 14ºC) shallow sea in a sunlight/darkness-stressed setting. Detailed study of fossil organisms from environments no longer represented is necessary if – among other things – we are to understand the nature and degree of environmental control on their life history. We describe the association of encrusting and boring organisms developed on the gastropod Antarctodarwinella ellioti Zinsmeister, 1976, from the lower section of the La Meseta Formation exposed along the northern tip of Seymour Island. The age of the rocks bearing the fossil fauna considered is middle Eocene, i.e., ca. 45 Ma. a Chi square Independence Test revealed that the community of encrusting and boring organisms recorded on Antarctodarwinella ellioti – dominated by polychaetes and bryozoans – shows a clear preference for the aperture interior area of the shell. A subsequent Cochran Q Test indicated that the differences in frequency of encrusting and boring organisms as counted on the different aperture interior sectors were statistically significant. Thus, polychaetes, boring bryozoans, and encrusting bryozoans, do not show the same frequency in each sector of the aperture interior, i.e., they are more frequent on the columella (p