Primer registro de Cardiatherium chasicoense (Rodentia, Hydrochoeridae) fuera del área pampeana (Argentina) y su valor bioestratigráfico

a skull and associated mandible of a rodent found in the arenisca albardón member, loma de las tapias formation, san juan province,argentina, is studied. it is assigned to the species cardiatherium chasicoense (hydrochoeridae), being the single record of this species out of its type locality, arroyo chasicó, buenos aires province. in addition, this is the single remain with skull and mandible in association, which permits corroboration of the assignment to this species of isolated upper teeth found in the type locality. this specimen was compared qualitatively with all the species of cardiatherium so far recognized, and was included in geometric morphometric analyses in order to compare morphological features that could not be evaluated through linear measurements. the specimen is a juvenile, and proved to fit within the model proposed for ontogenetic growing of cheek teeth for late miocene capybaras. its assignment to c. chasicoense permits the correlation of the bearing levels with those of the type locality, lithofacies association 3 (las barrancas member) of the arroyo chasicó formation, suggesting an age of ca. 7 ma for these latter, on the basis of a dating of the middle section of the arenisca albardón member which yielded 7.0 + 0.9 ma. the bearing sediments are interpreted as deposited by a braided river. so far, all the records of fossil capybaras have been found in water-related sediments, in accordance with the semiaquatic habits of their modern representatives.