Dinosaur tracks from aeolian deposits of the Hauterivian Avilé Member (Agrio Formation), northwestern Patagonia, Argentina

Abstract

This study describes several dinosaur tracks from the non-marine deposits of the Avilé Member (Agrio Formation, Lower Cretaceous) in northwestern Patagonia, Argentina. During the Hauterivian, a basin-scale regressive event led to deposition of the Avilé Member, characterised by fluvial and aeolian deposits. At the Mina San Eduardo locality, the ichnites are preserved as concave epireliefs within medium-grained sandstones, corresponding to wet interdune facies. Most of the tracks exhibit a poor morphological quality, probably because they represent undertracks. The ichnoassemblage includes medium- to large-sized kidney- to horseshoe-shaped tracks assigned to sauropods, pentadactyl and tetradactyl tracks tentatively assigned to cf. Tetrapodosaurus isp. (with a probable affinity to ankylosaurian thyreophorans rather than stegosaurians), and isolated tridactyl tracks referred to undetermined bipedal dinosaurs. Notably, some tracks exhibit a frontward-deepening profile, resulting in a marked inclination of the track plane relative to the original tracking surface. Kidney- to horseshoe-shaped tracks display significant extramorphological features, such as posterior sediment mounds which, in specific instances, are truncated by sharp cuts revealing invertebrate burrows. These features provide key insights into the substrate rheology and moisture conditions at the time of track formation. In the absence of dinosaur skeletal remains within the Agrio Formation, this diverse ichnological record serves as the primary proxy for reconstructing the palaeobiology and palaeoecology of the dinosaurs in these environments. Furthermore, the Avilé Member represents one of the few South American tracksites where sauropod and thyreophoran tracks co-occur within an aeolian depositional setting.