ORIGIN OF VIVIPARISM IN CYPRINODONTIFORMES (TELEOSTEI: ATERINOMORPHA): WHAT DO WE KNOW SO FAR?

E. SFERCO; AGUILERA, G.; MIRANDE, J. M.

Salta

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2022

IBIGEO, UnSa

Viviparism has evolved independently at least 12 times in ray-finned fishes. However, the fossilrecord of actinopterygian viviparism is poor, with only few documented occurrences. TheCyprinodontiformes are the most diversified group of atherinomorph fishes. Within the order, thefamilies Goodeidae, Anablepidae and members of the Poeciliidae are viviparous, inhabitingfreshwater and brackish environments from Mexico to central Argentina. These families arecharacterized by the modification of the male anal fin into a gonopodium, which allows internalfertilization. Anablepid and poeciliid male anal fin is completely modified whereas the anal fin isonly slightly modified in goodeid males. Here we summarise the fossil records of viviparouscyprinodontiform families known so far, based on our studies in Argentinian taxa and on literaturewhen taxa from other countries. Oldest goodeids are known from the late Miocene of Mexico,where the fossil species Tapatia occidentalis is found, clearly exhibiting a modified anal fin andindicating plausible viviparism. Fossil representatives of living goodeid genera occur in Plioceneand Pleistocene sediments from Mexico and USA. Even though poeciliids are nowadays abundantin Central and South America, its fossil record is really scarce. Putative poeciliid scales werereported in the Pliocene of Brazil and the oldest undisputed viviparous poeciliid is a fossil species of the living genus Poeciliopsis from the Pleistocene of Mexico. Anablepid fossil record is richer, with four species described in recent years from Miocene deposits of Northwestern and CentralArgentina: Tucmanableps cionei, Sachajenynsia pacha (both from the middle Miocene),Sanjuanableps calingasta and the first fossil species of the living genus Jenynsia: Jenynsia herbsti(both from the late Miocene). All these taxa show sexual dimorphism, but our analysis indicates that the gonopodium is incipient, formed by all rays in males of S. pacha, well-differentiated in both S. calingasta and J. herbsti, with four enlarged rays; and very complex, formed by rays 2–7 crowding together and twisting around each other, with a bilobed plate in the distal end in T. cionei. Although we cannot undoubtedly infer reproduction through internal fertilization for S. pacha, it was present in the remaining anablepid fossil species. Similarly, internal fertilization has been also proposed for all known fossil goodeids and Poeciliopsis. This not only suggests that internal fertilization was already present in the Miocene, at least for anablepids and goodeids, but also that live bearing or viviparism might have been possible in these families since its early diversification during the Miocene.*Financial support: FONCYT PICT-2016-1263.