Gastropod predatory traces recorded in the oyster Gryphaeostrea callophyla (Ihering) from the Roca Formation (Danian, Argentina)

BREZINA, S.; CASADÍO, S.; ARCHUBY, F.

General Roca

Otro; Reunión Anual de la Asociación Paleontológica Argentina; 2012

Asociación Paleontológica Argentina

Drilling predation traces provide the opportunity to quantify prey-predator interactions in the fossil record. Moreover, they are rich in behavioral and ecologic information. Gastropod predatory boreholes are assigned to the ichnogenus Oichnus Bromley, 1981. The aim of this work is to evaluate preferential distribution of Oichnus isp. in shells of G. callophyla, a free-lying oyster registered in the lower part of the Roca Formation (Danian). This species inhabited muddy bottoms in full marine environment. The sample include 178 specimens from General Roca (n= 82) and Cerros Bayos (n= 96), Northern Patagonia. The predatory boreholes were recorded on standardized maps of the valves. These maps show different areas established on the basis of morphological differences likely to influence the site selection by predators. 16 predatory boreholes (14 in left valves and 2 in right valves) were registered, but only one was successful. Goodness of fit test and exact confidence intervals for the binomial distribution were performed in order to assess preference of predators on different sectors of the valves. Results showed no preferential distribution for valves or areas, but a significant difference between localities (p< 0.001). Cerros Bayos is the locality with highest percentage of drilling predation (93.8 %).