Snakes from the Cerro Azul Formation (Upper Miocene), Central Argentina, with a review of fossil viperids from South America

Abstract

ABSTRACT South America contains a diverse Miocene snake record. Heretofore, the most significant assemblages were from the early and middle Miocene of Patagonia and Colombia. Colubroid vertebrae assignable to the ‘Colubridae’ and Viperidae are here reported from the upper Miocene Cerro Azul Formation at Caleufú, in La Pampa province, central Argentina. The viperid fossil is the oldest record of the family in South America and, together with molecular evidence, it supports the hypothesis of viperids first entering South America prior to the closure of the Isthmus of Panamá. South American viperid specimens also have been recognized from the Pliocene (aff. Bothrops) and Pleistocene of Buenos Aires province, Argentina. The presence of Bothrops during the early–middle Pleistocene near La Plata city suggests that during more humid intervals this genus had a wider distribution than at present. A previous report of a viperid from the late Pleistocene of Bolivia cannot be corroborated.