Fresh-water shark teeth from the Triassic Paramillo Formation in the Mendoza Precordillera, Argentina

ALBANESI, GUILLERMO LUIS; JOHNS, MARGIE; VOLDMAN, GUSTAVO GABRIEL

Buenos Aires

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2009

Asociación Paleontológica Argentina

A collection of over 550 elasmobranch fossil fish teeth was obtained from the ParamilloFormation, in northwestern Mendoza Province. The strata are exposed between the ElBalcón and Paramillo localities, in the Mendoza Precordillera. At ca. 2800 m altitude,the upper part of the Paramillo Formation consists of a series of black shalesinterbedded with andesitic sills that are E-W trending and slightly dipping N. A 20 mthick interval with black shales and intercalating lensoidal calcarenites representscontinental shallow lake environments. About 13.6 kg of calcarenite samples from thebasal level were digested by conventional acid-etching techniques. The onlymicrofossils recovered from the insoluble residue were the teeth of fresh-water sharks,Triassic in age, and found for the first time in Argentina. The teeth are new forms fromthe genus Lissodus, have the characteristic low crown and labial peg, and show somesimilarities to other Middle–Late Triassic Lissodus species. A Middle Triassic age is inagreement with previous paleofloral data from correlative strata cropping out severalkm south of the study area in the Potrerillos locality. Initial analysis of the color of theteeth (black) indicates an Ichthyolith Alteration Index (IAI)/Conodont Color AlterationIndex (CAI) value of 4–5 (190–480°C).