New bioerosion trace produced by byssate bivalves on Recent oyster shells.

ROMERO, M.V.; BREZINA S.S.; BREMEC, C.S.; CASADÍO, S.

General Roca

Congreso; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA (RACAPA 2012); 2012

Asociación Paleontológica Argentina-Instituto de Investigaciones en Paleobiología y Geología-Universidad Nacional de Río Negro

Byssate bivalves can be permanently or temporarily attached to hard substrates by byssal threads. Dissolution of the substrate to which they are attached may leave superficial bioerosion traces. Fixichnia include these superficial structures produced by epifaunal organisms that anchor or fix themselves to the substrate using soft or skeletal body parts. This study reports the scars produced by the byssus of Mytilus edulis Linnaeus, 1758 and Aulacomya atra (Molina, 1782) recorded in shells of Ostrea puelchana d´Orbigny, 1842. Oyster valves were cut using a silicon carbide abrasive cutter and then gold-sputtered prior to SEM observation. Each byssal thread leaves a characteristic scar on shells substrate. They etch an irregular trace on the substrate which may reach a diameter of several centimeters. These etching-traces comprise shallow round/oval holes of variable number and placement. A bundle of pits corresponding to fibers that compose the thread core was identified in the interior of each hole. The byssal etchings are easily differentiated from the others fixation ichnotaxa. The description of this trace would allow adjusting the composition of fossil assemblages and therefore paleoenvironmental interpretations in those cases in which mytilid shells have not been preserved. In addition, the recognition of this trace along with other ones of tracemakers with reotaxis or positive phototaxis could be useful in inferring the life habit of fossil substrates and in reconstructing their taphonomic history.