Implications of the recent modifications in the Late Triassic time-scale to tetrapod-bearing assemblages

EZCURRA, M.; DESOJO, J.B.

MACN, Ciudad Autónoma de Buenos Aires, Argentina.

Otro; Reunión Anual de comunicaciones de la Asociación Paleontológica Argentina y Conferencias: “Darwin, Lamark y la Teoría de la evolución de las especies”,; 2009

APA

Recent changes of the Late Triassic time-scale have resulted in modifications in the age of its stage boundaries. A longer Norian and a shorter Carnian are recognized, in which the Carnian-Norian boundary is situated at 228 mya and the Norian ends at 210 mya. Accordingly, based on these new chronostratigraphic settings, the age of deposition of Late Triassic sedimentary units and that of macroevolutionary events (e.g. the so-called “Carnian-Norian extinction”) weretemporally re-scaled. A clear example of these modifications is appreciated in the age of the Ischigualasto Formation (Ischigualasto-Villa Unión Basin, northwest of Argentina), in which its time of deposition is re-assigned to the late Carnian-early late Norian time span. The re-scaled age of the Ischigualasto Formation allocates the First Apperance Datum of several tetrapod groups (e.g. aetosaurs, crocodylomorphs, phytosaurs, dinosaurs) in the late Carnian insteadof the early Carnian. These temporal re-scalings and recent radimetric datings of the Chinle Formation (USA) allow to compare its tetrapod faunas with those of South America in a well-constrained temporal range. Clear distinctions are observed between these tetrapod-bering assemblages, such as the presence of coelophysoids, desmatosuchine aetosaurs,and phytosaurs in North American and rhynchosaurus, sauropodomorphs, ornithischians, and proterochampsids in southern faunas. These differences bolster the hypotheses of faunistic provincialims in the Late Triassic, pointing out the necessity of studying the macroevolutionary events that take part in Late Triassic terrestrial biotas not only as simple processes at a world-wide scale, but also as more complex interrelated processes that occured at a more regional level.