TOURNAISIAN (LOWER CARBONIFEROUS) ACTINOPTERYGIAN AND SARCOPTERYGIAN FISH REMAINS FROM AGUA DE LUCHO FORMATION, LA RIOJA, ARGENTINA

SFERCO, MARTA EMILIA; RUSTÁN, JUAN JOSÉ; VACCARI, NORBERTO EMILIO; STERREN, ANDREA FABIANA; BALSEIRO, DIEGO; EZPELETA, MIGUEL; PRESTIANNI, CYRILLE; ASTINI, RICARDO ALFREDO

Congreso; Reunión Anual de Comunicaciones de la APA; 2022

Upper Palaeozoic osteichtyan fossil record is rather abundant in South America (especially in Uruguay, Bolivia and Chile), however it is scarce and represented by few late Carboniferous and lower Permian isolated scales and bone remains in Argentina. Here we present well preserved osteichthyan remains from Agua de Lucho Formation (Sierra de las Minitas, Río Blanco Basin, La Rioja province, Argentina), considered middle to late Tournaisian in age based on palynological data and biostratigraphic correlations. The unit is composed of approximately 1250 m of marine siliciclastic lithofacies, recording glacigenic and deltaic environments. Fishes were collected from four stratigraphic intervals. The lowermost, interval 1, bears actinopterygian remains in nodules within massive mudstones underlying diamictitic beds, including isolated bones and a remarkable articulated specimen, preserving the right opercular bones, cleithrum and a branchiostegal plate, pectoral fin and the anterior portion of the trunk showing articulated scales mainly in medial view. The scales are typically ganoid, with a peg and socket articulation, rectangular (deeper than long), strongly serrated posteriorly, exhibiting a high peg and anterior process. Interval 2 includes a tetrapodomorph sarcopterygian skull roof bone and an actinopterygian branchiostegal plate preserved as molds in fine-grained sandstones, around the marker palynomorph level of Waltzispora lanzonii. Both intervals also record abundant and diverse invertebrate fauna and plants. Interval 3, corresponding to levels with the plants Pseudosporogonites cf. hallei and Porongodendron minitensis, bears isolated actinopterigyan bones (i.e., maxilla, nasal) and smooth longer than deep, posteriorly serrated scales, exhibiting a short peg and anterior process. Fishes occur in fine-grained sandstones, only accompanied by abundant plants. Finally, an isolated actinopterygian subopercle occurs within the mudstones of interval 4, associated only with abundant invertebrate fauna. All studied actinopterygian bones are ornamented with densely packed ganoin tubercles and short, confluent ridges, whereas posteriorly serrated scales are only smoothly ornamented with low ridges. Similar bone ornamentation is found in Devonian early actinopterygians (i.e Mimipiscis) but similar scale configuration and ornamentation occurs in many Carboniferous early actinopterygian groups (like Radinichthyidae), both with a broad Gondwanan distribution. In South America, Devonian early actinopterygians are mostly found in Bolivia whereas Carboniferous early forms have been mainly recovered from Upper Carboniferous and Lower Permian deposits of Uruguay. The detailed anatomical study of these remains will not only improve our knowledge on early actinopterygian evolution and diversification but will also be important to understand its paleobiogeographic implications, within South America and with the rest of Gondwana. *Proyecto subsidiado por: ANPCyT PICT 3095-2017 y SECyT UNLAR 530 00-05103/2019.