A new genus and species of Heroini (Perciformes: Cichlidae) from the early Eocene of southern South America

Abstract

The Lumbrera Formation is the uppermost unit of the Salta Group, which crops out in northwestern Argentina. The paleoenvironment of the Lumbrera Formation is interpreted as a perennial lake deposited under temperate climatic conditions during the early to middle Eocene. Its fossil content is made up of palynomorphs, insects, crocodiles, turtles, lizards, and mammals, besides an ichthyofauna formed by cichlids, poeciliids and dipnoans. †Plesioheros chauliodus is described based on a single individual from this formation, which was fossilized as a lateral view impression (missing anal and caudal fins). It can be distinguished from other cichlids by a moderately deep body, enlarged anterior dentary teeth bearing subapical cusp, a low abdominal vertebral count (10), five canal openings in the dentary, and XI + 12 dorsal-fin rays. A phylogenetic analysis, using the matrix by Kullander (1998), recovered †Plesioheros within Heroini. This species was recovered most closely related to Australoheros and to the deep-bodied South American heroins. The occurrence of an Eocene Heroini, as well as of other cichlid lineages in the same stratigraphical level, is evidence of an ancient diversification in this family. This ancient age supports the hypothesis that the Cichlidae originated on Gondwana.