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

BREZINA, SOLEDAD; CASADÍO, SILVIO; ARCHUBY, FERNANDO M

General Roca, Río Negro

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2012

Asociación Paleontológica Argentina

Drilling predation traces provide the opportunity to quantify prey-predator interactions in thefossil record. Moreover, they are rich in behavioral and ecologic information. Gastropodpredatory boreholes are assigned to the ichnogenus Oichnus Bromley, 1981. The aim of thiswork is to evaluate preferential distribution of Oichnus isp. in shells of Gryphaeostreacallophyla (Ihering, 1903), a free-lying oyster registered in the lower part of the RocaFormation (Danian). This species inhabited muddy bottoms in fully marine environment. Thesample include 178 specimens from General Roca, Río Negro (n= 82) and Cerros Bayos, LaPampa (n= 96), Northern Patagonia. The predatory boreholes were recorded on standardizedmaps of the valves. These maps show different areas established on the basis ofmorphological differences likely to influence the site selection by predators. 16 predatoryboreholes (14 in left valves and 2 in right valves) were registered, but only one wassuccessful. Goodness of fit test and exact confidence intervals for the binomial distributionwere 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 differencebetween localities (p< 0.001). Cerros Bayos is the locality with highest incidence of drillingpredation (15/16 attacks).