The rise of internal fertilization in the Anablepidae (Teleostei, Cyprinodontiformes): two new genera and species from the Miocene of Tucumán, Argentina

Abstract

Two new genera and species of Cyprinodontiformes from the Miocene of Tucumán, Argentina, are described: Tucmanableps cionei and Sachajenynsia pacha. Both exhibit sexual dimorphism, indicated by the modification of the male anal fin into an intromittent organ; tricuspid teeth in the jaws; abdominal pelvic fins and other features that demonstrate a relationship with the family Anablepidae. Males of Sachajenynsia pacha gen. et sp. nov. present modifications of the anal fin, herein interpreted as an incipient gonopodium, whereas the anal fin of Tucmanableps cionei gen. et sp. nov. is modified into a complex gonopodium with a median distal plate, which is unique among the Anablepidae. In extant genera of the family, modification of the anal fin into an intromittent organ is related to internal fertilization; this condition is inferred for S. pacha but was clearly the reproductive mode of T. cionei. In our phylogenetic analysis, S. pacha is recovered as the sister group of all anablepids with evident internal fertilization, while T. cionei forms a clade with Anableps species. The occurrence of two new anablepid genera showing distinct and unique morphologies suggests that the fossil diversity of the Anablepidae may be higher than the extant one. Also, the new taxa were found in open lake deposits with coastal and inner lake sediments of the Río Salí Formation associated with the Miocene Entrerrian–Paranense Marine Ingression, supporting the idea that coastal environments and brackish waters are related to the generic diversification of the Anablepidae, as was suggested for the species of Jenynsia.

Molecular and morphological convergence to sulfide-tolerant fishes in a new species of Jenynsia (Cyprinodontiformes: Anablepidae), the first extremophile member of the family

“…The phylogenetic analysis herein performed under parsimony combining morphological and molecular data matrices and including known fossil taxa [34, 35], has resulted in a new hypothesis of relationships that present differences with previous hypothesis. Unlike the results presented by Bogan et al .…”

“…Nevertheless, the phylogenetic placement of the three recently described extinct taxa agrees with that proposed by Sferco et al . [35], Bogan et al . [34], as well as the relationships of the subgenus Plesiojenynsia recently proposed by Amorim and Costa [36].…”

Multigene phylogeny supports diversification of four-eyed fishes and one-sided livebearers (Cyprinodontiformes: Anablepidae) related to major South American geological events

“…The present distribution pattern of Jenynsia is also similar to that found for other aquatic organisms which the distribution is attributed to the Paranean Sea, including the freshwater Crustacean families Palaemonidae, Sergestidae and Trichodactylidae [ 69 ]. Both known fossil genera of Anablepiadae were found in an area previously occupied by the Paranean Sea [ 9 ]. The presence of Tucumanableps , the sister group of Anableps , and Sachajenynsia , the sister group of all genera of Anablepidae except Oxyzygonectes , in this area also corroborates the ancient connections between Amazon and Paraná river basins.…”

“…The third point was placed in the divergence between Anableps and Jenynsia , this position corresponds to the Tucumanableps cionei Sferco, Herbst, Aguilera & Mirande, 2017. This species is recognised as the sister goup of Anabelps from the Meddle Miocene of the Río Sali formation, Argentina [ 9 ], with 12 Ma (prior settings: lognormal distribution, mean = 12 and standard deviation = 0.5). The position of each calibration points is also shown in Fig 2 .…”

“…However, after a detailed analysis of the type series of Carrionellus diumortuus White, 1927, the genus was then realocated in the Cyprinodontidae family [ 8 ]. In a recent study two new monotypic genera from Middle Miocene of Northern Argentina were described in the family Anablepidae, Tucumanableps Sferco, Herbst, Aguilera & Mirande, 2017, recovered as the sister group of Anableps , and Sachajenynsia Sferco, Herbst, Aguilera & Mirande, 2017, the sister of all other genera of Anablepidae except Oxyzygonectes [ 9 ].…”