Macro and Micro Morphology of Scales from an Endemic South American Actinopterygii Family (Pseudobeaconiidae, Santa Clara Abajo Formation)

BENAVENTE, CECILIA ANDREA; GIORDANO, PAULA; SUAREZ DAVI, SOFÍA

Congreso; XII Congreso Argentino de Paleontología; 2021

Detailed morphological information about scales of Pseudobeanoiidae is scarce, especially the one related to micromorphology. Pseudobeaconiidae is a South American endemic Actinopterygii family only recorded in the Triassic Cuyana rift Basin. The main goal of this communication is to provide novel micromorphological data of scales of Pseudobeaconiidae, along with macromorphological data from new material. The studied specimens were recovered from the center lake facies of the Santa Clara Abajo Formation (El Peñasco Group, Santa Clara sub-basin, northern Mendoza province) with detailed stratigraphic control. The material has not been assigned to any known species yet and is housed in the Paleovertebrate Collection of the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA). Material includes: IANIGLA-PV 881, 883a, 884a, 890, 891a, 891b, 892a, and fragmented not cataloged specimens: M13, M66.1, M59. The specimens were mechanically prepared, and some of them were also prepared for histological and scanning electron microscopy microstudies. Macromorphology shows ganoid-type scales with a distinct concentric pattern of ganoid ridges on the surface near the borders. These features have been reported for the scales of the family before. We also described new relevant characters like the presence of a well-developed peg-and-socket articulation and the presence of a medial keel. Regarding micromorphology, paleohistological slides show a lepisosteoid-type scale with the presence of multilayer ganoine and isopedine with canaliculi of Williamson, vascular canals, lacunae, and possibly Sharpey?s fibers. Scanning electron microscopy studies reveal smooth and no microtubercle surface. Detailed morphological data about scales in its stratigraphical context provides valuable information concerning postcranial patterns, such as type and shape variation of scales along the body, and sets the basis for further evolutionary trends assessment in basal Actinopterygii.