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MARSICANO Claudia Alicia

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Título:

Dating the non-marine Triassic of Argentina

Autor/es:

MARSICANO, CLAUDIA

Reunión:

Congreso; 11º Congreso de la Asociación Paleontológica Argentina; 2016

Resumen:

The Triassic Period represents a critical moment in the history ofnon-marinecommunities, characterized by remarkable change and innovation, and bracketed by the end-Permian andend-Triassic mass extinctions. One major difficulty with testing macroevolutionary patterns is the lack of precisebiostratigraphically-independent age constraints, critical in non-marine Triassic successions. Without precise independentage control, it is impossible todetermine if faunal variations among unconnected basins are a consequence ofdifferences in time,space, or a combination of both. Recently, new contributions tackled this problem providing high-precisionradiometric dates for two major Argentinian non-marine Triassic fossil-bearingsuccessions: the Puesto Viejo Group (San Rafael Basin) and the ChañaresFormation (Ischigualasto-Villa Unión Basin). Both units are well known because theirtetrapod record, including non-mammalian therapsids, non-archosaurarchosauromorphs, pseudosuchian archosaurs, and non-dinosaurian dinosauromorphs.These assemblages has long been considered Middle Triassic, based on tetrapodcorrelations and lithostratigraphic relationships. The new dates reveal that thetetrapod-bearing levels are younger in age, Carnian (Late Triassic), callinginto question current biostratigraphic correlations across Gondwana largelybased on non-mammalian therapsids. These successions include the classic MiddleTriassic assemblages from Brazil and southern Africa, which are devoid of otherindependent criteria for asserting their age. In this context, the Early-MiddleTriassic heterogeneous tetrapod composition across Gondwana attributed toprovincialism as a result of the end-Permian mass extinction might be just anartifact of overreliance on solely vertebrate biostratigraphy. The new Triassic dates from Argentina underlinehow precise geochronologic frameworks are essential for robust testing of macroevolutionaryand biogeographic hypothesis in the fossil record.

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