Análisis de huellas de vertebrados en la formación Allen, Valle de la Luna, Paso Córdoba, Río Negro, Argentina.

Abstract

The Área Natural Protegida de Paso Córdoba, located in the Río Negro province, is world-renowned for its diverse and abundant paleontological record. In recent years, the study of ichnological discoveries has experienced significant growth. In this Final Degree Project, a previously known locality within the area was studied, the Calvo site, in the Cañadón de la Tranquera, near Valle de la Luna Amarillo. The site displays an approximately 50 square meters surface, which preserves abundant vertebrate footprints in basal levels of the lower member of the Allen Formation (Malargüe Group, Neuquén Basin). At this site, at least four different types of vertebrate footprints have been preserved, each linked to a specific taxonomic group of producers. The first group of imprints includes indeterminate shorebird-type avian footprints, characterized by being tridactyl with narrow, separated digit impressions, wide angles, lateral symmetry, and a delicate, small-sized overall appearance. The second group corresponds to quadruped individuals and it is characterized by handprints with kidney-shaped, pentadactyl, laterally symmetrical impressions, with thick digital impressions with no claw traces, and subcircular foot impressions featuring digits with laterally recurved claw traces. Morphologically, these tracks are linked to sauropod titanosaurs. The third and fourth groupsconsist of tridactyl footprints with lateral symmetry, longer than wide, with a semi-triangular posterior border, and closed digit impressions with acuminated claws. Some of these footprints, referred to here as indeterminate tridactyl Type A, show impressions of thick, short digits and are associated with hadrosaurid ornithopod dinosaurs. The other group, called indeterminate tridactyl Type B, presents slender, elongated digit impressions and is attributed to medium- sized theropod dinosaurs. The surface may represent an ichnocenosis, with producers that were likely part of a paleocommunity either visiting the site to remain there or moving from one area to another without an apparent directionality. The taxonomic groups mentioned as possible producers are classified within the Allenian association. This site likely corresponds to a paleoenvironment of a floodplain with cyclical deposition, characterized by the presence of symmetrical ripple marks, abundant evidence of MISS formation, and traces of invertebrates, represented by numerous specimens of Skolithos isp. and a single specimen referred to as cf. Ophiomorpha isp. Thus, this site and its ichnological record complement the known ichnofauna of this stratigraphic interval.