Large-Diameter Burrows in the Upper Triassic Ischigualasto Formation, Northwestern Argentina

The Triassic Ischigualasto Formation, in northwestern Argentina, yield a rich and very well preserved paleovertebrate fauna, including the oldest dinosaurs, cynodonts, dicynodonts and an impressively diverse association of crurotarsian archosaurs, among others. Burrow complexes with multiple tunnels and chambers were found in the most fossiliferous layers of the Formation, stratigrafically located around 100 meters from the base. These burrow complexes are assigned to mouse-size tetrapods, more likely associated with the diverse and numerous Ischigualasto fauna of small carnivorous cynodonts. Similar structures founded in the Permo-Triassic layers in Africa, Antartic, and United States also had been assigned to carnivorous cynodonts. The age of the Ischigualasto Formation is very well known as Carnian based on two radiometric datation (227.8&plusmn0,3 for basal layers and 218&plusmn1,7 for the earliest layers on the top) consequently, these findings comprise the earliest record of tetrapod burrows in South America. The presence of large-diameter burrows in the Ischigualasto basin is remarkable because it has been located at ~40° of paleolatitude, which confirms the innovative idea of non latitudinal distribution of large non marine burrowing organisms. The Triassic simultaneous appearance of fossorial behavior throughout Pangea could be interpreted as a mechanism against adverse extreme seasonal climatic conditions that characterized this period.