Faunal and taphonomic characterization of the fish-bearing localities of the Cañadón Calcáreo Formation (Tithonian? Chubut, Argentina).

SFERCO, M.E., RAUHUT, O.W. M. & LÓPEZ-ARBARELLO, A.

Neuquén, Argentina

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

Universidad Nacional del Comahue

The Cañadón Calcáreo Formation (Tithonian?) mainly crops out on the margins of the middle section of the Chubut river, Chubut province, Argentina(Proserpio, 1987; Rauhut, 2006). This formation represents a coarsening upwards lacustrine to fluviatile sequence and, in its southern part, includes the so-called “Estratos de Almada”. These strata, which constitute the base of the formation and crop out all over the southern part of the outcrop area, bear a very important freshwater fish fauna. This fauna was first recognized in the first half of the past century (Piatnitzky, 1936), but, even though it constitutes one of the few Jurassic freshwater fish faunas in the fossil record (López-Arbarello, 2004; López-Arbarello et al. accepted), even its alpha taxonomy has not yet been solved. To date, two monospecific genera of teleosts and one species of a basal actinopterygian, Coccolepis groeberi Bordas, 1942, have been described. However, a higher diversity has been inferred. Based on preliminary studies of López-Arbarello and Arratia, at least one more species of teleost and more than one non-teleostean actinopterygian taxa are represented. The detailed study of the fish fauna is currently being done by the authors. During recent years, several campaigns carried out by Rauhut and López-Arbarello with the Museo Paleontológico “Egidio Feruglio” (MEF), have contributed to a better knowledge of the fish-bearing strata of the Cañadón Calcáreo Formation. The strata were recognized in at least six localities, and detailed profiles of two of them, Puesto Almada and Sierra de la Manea, are depicted herein. An analysis of the faunal composition of these fish-bearing localities and equivalent levels from Estancia Limonao and Estancia Fernández is presented. Every studied sample shows a considerable larger proportion of teleosts over coccolepids, as well as the frequent association of teleosts with coccolepid-like fishes. We also analyze for each and between localities, the preservation potential of the different parts of the fish skeleton (skull, pectoral and pelvic girdles, caudal fin) following six taphonomic categories, which comprise different articulation stages of the fish remains.