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

SFERCO, EMILIA; HERBST, RAFAEL; AGUILERA, GASTÓN; MIRANDE, J. MARCOS

Papers in Palaeontology

The Palaeontological Association

Año: 2017

Two new genera and species of Cyprinodontiformesfrom the Miocene of Tucuman, Argentina, aredescribed: Tucmanableps cionei and Sachajenynsia pacha.Both exhibit sexual dimorphism, indicated by the modificationof the male anal fin into an intromittent organ; tricuspidteeth in the jaws; abdominal pelvic fins and otherfeatures that demonstrate a relationship with the familyAnablepidae. Males of Sachajenynsia pacha gen. et sp. nov.present modifications of the anal fin, herein interpreted asan incipient gonopodium, whereas the anal fin of Tucmanablepscionei gen. et sp. nov. is modified into a complexgonopodium with a median distal plate, which is uniqueamong the Anablepidae. In extant genera of the family, modificationof the anal fin into an intromittent organ is relatedto internal fertilization; this condition is inferred for S. pachabut was clearly the reproductive mode of T. cionei. In ourphylogenetic analysis, S. pacha is recovered as the sistergroup of all anablepids with evident internal fertilization,while T. cionei forms a clade with Anableps species. Theoccurrence of two new anablepid genera showing distinctand unique morphologies suggests that the fossil diversity ofthe Anablepidae may be higher than the extant one. Also,the new taxa were found in open lake deposits with coastaland inner lake sediments of the Rıo Salı Formation associatedwith the Miocene Entrerrian?Paranense Marine Ingression,supporting the idea that coastal environments andbrackish waters are related to the generic diversification ofthe Anablepidae, as was suggested for the species of Jenynsia.