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Re: Dinosaurs rose faster than thought after redating of Triassic Chañares Formation in Argentina



The paper is now up on the PNAS website:

http://www.pnas.org/content/early/2015/12/03/1512541112

Abstract:

Dinosaurs have been major components of ecosystems for over 200
million years. Although different macroevolutionary scenarios exist to
explain the Triassic origin and subsequent rise to dominance of
dinosaurs and their closest relatives (dinosauromorphs), all lack
critical support from a precise biostratigraphically independent
temporal framework. The absence of robust geochronologic age control
for comparing alternative scenarios makes it impossible to determine
if observed faunal differences vary across time, space, or a
combination of both. To better constrain the origin of dinosaurs, we
produced radioisotopic ages for the Argentinian Chañares Formation,
which preserves a quintessential assemblage of dinosaurian precursors
(early dinosauromorphs) just before the first dinosaurs. Our new
high-precision chemical abrasion thermal ionization mass spectrometry
(CA-TIMS) U–Pb zircon ages reveal that the assemblage is early Carnian
(early Late Triassic), 5- to 10-Ma younger than previously thought.
Combined with other geochronologic data from the same basin, we
constrain the rate of dinosaur origins, demonstrating their relatively
rapid origin in a less than 5-Ma interval, thus halving the temporal
gap between assemblages containing only dinosaur precursors and those
with early dinosaurs. After their origin, dinosaurs only gradually
dominated mid- to high-latitude terrestrial ecosystems millions of
years later, closer to the Triassic–Jurassic boundary.


-- 
David Černý