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

E. SFERCO; RUSTÁN, J.J.; VACCARI, E.; STERREN, A.F.; BALSEIRO, D.; EZPELETA, M.; CISTERNA, G.A.; PRESTIANNI, C.; MUÑOZ, D.F.; ASTINI, R.

Salta

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

IBIGEO, UnSa

Upper Palaeozoic osteichtyan fossil record is rather abundant in South America (especially inUruguay, Bolivia and Chile); however, it is scarce and only represented by few late Carboniferousand early Permian isolated scales and bone remains in Argentina. Here we present well-preservedosteichthyan remains from the Agua de Lucho Formation in Sierra de las Minitas, Río BlancoBasin, La Rioja province, Argentina. This is a marine siliciclastic succession (1250 m thick),recording glacigenic and deltaic environments of middle to late Tournaisian age, based onpalynological data and biostratigraphic correlations. Fishes were collected from four stratigraphicintervals. The lowermost, interval 1, bears actinopterygian remains in nodules within massivemudstones underlying diamictitic beds, including isolated bones and a remarkable articulatedspecimen, preserving the right opercular series, cleithrum, a branchiostegal plate, pectoral fin andthe anterior portion of the trunk showing articulated scales mainly in medial view. The scales aretypically ganoid, with a peg and socket articulation, rectangular (deeper than long), strongly serratedposteriorly, exhibiting a high peg and anterior process. Interval 2 includes a tetrapodomorphsarcopterygian skull roof bone and an actinopterygian branchiostegal plate preserved as molds infine-grained sandstones, around the marker palynomorph level of Waltzispora lanzonii. Bothintervals also record abundant and diverse invertebrate fauna and plants. Interval 3, located slightlyabove levels with the plants Pseudosporogonites cf. hallei and Porongodendron minitensis, bearsisolated actinopterygian bones (i.e., maxilla, nasal) and smooth longer than deep, posteriorlyserrated 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 withinthe mudstones of interval 4, associated only with abundant invertebrate fauna. All studiedactinopterygian bones are ornamented with densely packed ganoin tubercles and short, confluentridges, whereas posteriorly serrated scales are only smoothly ornamented with low ridges. Similarbone ornamentation is found in Devonian early actinopterygians (i.e, Mimipiscis), but similar scaleconfiguration and ornamentation also occur in many Carboniferous actinopterygian groups (likeRadinichthyidae); both with a broad Gondwanan distribution. In South America, Devonian earlyactinopterygians are mostly found in marine deposits of Bolivia, whereas Carboniferous forms havebeen mainly recovered from upper Carboniferous marine deposits of Uruguay. The detailedanatomical study of these remains will not only improve our knowledge on early actinopterygianevolution and diversification, but will also be important to understand its paleobiogeographicimplications, within South America and the rest of Gondwana.