Just out @ Gondwana Research
U-Pb age constraints on dinosaur rise from south Brazil
Max C. Langer, Jahandar Ramezani, Átila A.S. Da Rosa
Triassic dinosaurs from South Brazil are considered as some of the oldest known worldwide, but their precise correlation to other early dinosaur occurrences have proven difficult. The problem of such long-distance faunal correlations has been exacerbated by reliance on an equivocal tetrapod biostratigraphy and the lack of palynomorphs and other age-bearing microfossils. Here, we present new high-precision U-Pb zircon geochronology (CA-ID-TIMS method) from two classical dinosaur-bearing fossil sites in south Brazil; a weighted mean 206Pb/238U date of 233.23 ± 0.73 Ma (2σ complete uncertainty) from the Santa Maria Formation and a single zircon 206Pb/238U date of 225.42 ± 0.37 Ma representing the maximum age of the Caturrita Formation. The new age results, combined with available geochronology from other Triassic dinosauromorph occurrences, allow establishing a chronostratigraphic framework for the Late Triassic appearance of dinosaurs in western Pangea. Within this context, the major macroevolutionary events associated with the rise of dinosaurs can be recognized and their possible links to coeval paleoenvironmental and biotic shifts can be examined.
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