The Lumbrera Formation is the uppermost unit of the Santa Bárbara Subgroup of the Salta Group, exposed in northwestern Argentina. It consists of fine clastic sediments of characteristic brick red color with an intercalation of green mudstone levels, which are called Faja Verde. The specimen described here was collected from the middle part of the Faja Verde II at the Alemania locality in sediments dated as Eocene. The material comprises a specimen, preserved as part and counterpart, which is assigned to a new genus and species: Proterocara argentina, gen. et sp. nov. The phylogenetic analysis to establish its position within Cichlidae was based on a matrix with 51 taxa and 91 characters. The most parsimonious tree shows P. argentina as sister group of the clade formed by the subfamilies Cichlasomatinae and Geophaginae based on three characters: articulating process of premaxilla moderately distinct, first hemal arch on last abdominal vertebra, and 13–14 pectoral-fin rays. Two autapomorphies are recognized for P. argentina: ascending arm of premaxilla as long as dentigerous arm, and dorsal lateral line on caudal fin between caudal rays D2 and D3. Extant members of the family Cichlidae live mostly in lentic freshwater bodies, corroborating the lacustrine paleoenvironment assigned to this formation.