CONICET | Buscador de Institutos y Recursos Humanos

Sauropod tracks provide interesting information about the social behavior and locomotion of these herbivore dinosaurs, the largest terrestrial animals to have ever existed. Although this ichnological record is relatively abundant, most sauropod ichnospecies are poorly preserved. Agua del Choique is a new Late Cretaceous sauropod track site discovered by our team in Malargüe, Mendoza Province, Neuquén Basin, Argentina. This discovery was made while conducting fieldwork for a project focused on the systematic, taphonomic and paleoecologic aspects of dinosaurs, mammals and flora from the Late Cretaceous-Paleogene of Mendoza. This track site is located in the Loncoche Formation, late Campanian early Maastrichthian in age, and is one of the youngest sauropod tracks site recorded in the world. Agua del Choique track site represents a lake setting and river-dominated delta deposits, and comprises at least 200 well-preserved tracks, located on a calcareous sandstone bed. These tracks are caracteryzed by a wide-gauge trackway and pronounced heteropody (manus-pes area ratio of 1:3). It is an excellent case study of the wide-gauge style of locomotion produced by Late Cretaceous derived titanosaurs that have no impression of manual phalanges. These features, and the fossil record from the Loncoche Formation, suggest that the trackmakers were, probably, middle size saltasaurine or aeolosaurine titanosaurs (14-16 m long). The analyses of the palynological content of the pelitic strata, located above and below the track bed, gave new evidences to the paleoenvironmental reconstruction of the site. The palynological association above the tracks level is dominated by fresh water algae: Pediastrum sp.aff. P. boryanum var.longicorne Reinsch and Pediastrum sp.aff.P.duplex Meyen; Botryococcus spp.; peridinioid dinoflagellate cysts and a few specimens of Ovoidites and Tetraporina. The association found below the track level is dominated by Pediastrum sp.aff. P. boryanum var. brevicorne A.Br. and Botryoccocus spp. The algae represent the autochthonous vegetation of the water body, so in this case the dominance in all the samples of the fresh water algae Pediastrum would be indicative of lakes with eutrophic to hypertrophic water, small ponds or certain lowland rivers, with alkalinity that could be above the neutral pH. The occurrence of monospecific peridinioid cysts in the palynological association and the lack of other marine taxa would indicate that these dinoflagellate cysts were deposited in a fresh to brackish water environment. In summary, a lacustrine environment dominates this portion of the section but with evidence of intermittent tidal influence.