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.A Formação Lumbrera é a unidade do topo do Grupo Salta, aflorante na região noroeste da Argentina. O paleoambiente da Formação Lumbrera tem sido interpretado como um lago perene depositado sob um clima temperado durante o início do Eoceno. Seu conteúdo fóssil é formado por palinomorfos, insetos, crocodilos, tartarugas, lagartos, mamíferos, além de uma ictiofauna que inclui ciclídeos, poeciliídeos e dipnóicos. †Plesioheros chauliodus é descrito com base em um único indivíduo coletado nesta formação, preservado como impressão em vista lateral (faltando as nadadeiras anal e caudal). Ele pode ser distinguido de outros ciclídeos por um corpo moderadamente alto, dentes anteriores do dentário aumentados e portando uma cúspide lingual subapical, uma baixa contagem de vértebras abdominais, cinco aberturas do canal sensorial no dentário, e XI + 12 raios na dorsal. Na análise filogenética, usando a matriz apresentada por Kullander (1998), †Plesioheros resultou dentro da Tribo Heroini mais relacionado a Australoheros e aos heroinis de corpo alto sul-americanos. A ocorrência de um heroini fóssil desta idade, bem como das outras linhagens de ciclídeos no mesmo nível estratigráfico, é uma evidência da diversificação inicial da família, corroborando fortemente a hipótese de que os Cichlidae se originaram no Gondwana ainda durante o Cretáceo.

Temporal Patterns of Diversification across Global Cichlid Biodiversity (Acanthomorpha: Cichlidae)

“…1), which is consistent with the known fossil distributions of the oldest described cichlid taxa from these geographic lineages, extending to the Eocene approximately 40 to 49 Ma (e.g. [28], [32], [33]). While Cretaceous-age fossils are currently lacking for the family Cichlidae, a vicariant origin for the family cannot be refuted by the lack of fossils.…”

“…While Cretaceous-age fossils are currently lacking for the family Cichlidae, a vicariant origin for the family cannot be refuted by the lack of fossils. The East African and Argentinian fossils establish a minimum age for cichlids at ∼40–46 Ma [28], [29], [31], [32], [33] and double the age of cichlids from previously known fossil specimens. Our divergence-time estimates are consistent with both the sequence and timing of Gondwanan breakup, and they indicate that the diversification of cichlid lineages may have occurred in the Mesozoic.…”

“…A number of fossil cichlids are also known from South America, specifically from Brazil and Argentina, with specimens dating from the Miocene to the Eocene [30], [31], [32], [33]. A number of new fossil cichlid taxa from the Neotropics have recently been described that represent some of the oldest known cichlids, dating back to the Eocene (approximately 40–49 Ma, [32], [33]). The placement of these fossils has necessarily been based on morphological phylogenetic studies incorporating extant and extinct taxa [32], [33].…”

“…A number of new fossil cichlid taxa from the Neotropics have recently been described that represent some of the oldest known cichlids, dating back to the Eocene (approximately 40–49 Ma, [32], [33]). The placement of these fossils has necessarily been based on morphological phylogenetic studies incorporating extant and extinct taxa [32], [33]. These recently discovered extinct taxa present an opportunity to utilize several novel fossil calibrations for investigating estimates of cichlid divergence times not available to previous researchers.…”

Molecular and fossil evidence place the origin of cichlid fishes long after Gondwanan rifting

“…However, the stratigraphically oldest fossil cichlids are Eocene in age (approx. 46 Ma) [12,13], implying a gap of approximately 90 Myr in the early history of the group. This, along with the absence of Early Cretaceous fossils belonging to more inclusive and taxonomically diverse clades that contain cichlids, has led some to abandon the orthodoxy of Mesozoic vicariance in favour of Cenozoic dispersal to explain the present-day distribution of cichlids [12,14].…”