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

Many thanks to David Černý for noting the paper is now online.

Just for the record, the full reference:

Claudia A. Marsicano, Randall B. Irmis, Adriana C. Mancuso, Roland
Mundil, and Farid Chemale (2015)
The precise temporal calibration of dinosaur origins.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1512541112

Many hypotheses have been put forth to explain the origin and early
radiation of dinosaurs, but poor age constraints for constituent
fossil assemblages make these scenarios difficult to test. Using
precise radioisotopic ages, we demonstrate that the temporal gap
between assemblages containing only dinosaur precursors and those with
the first dinosaurs was 5–10 million years shorter than previously
thought. Thus, these data suggest that the origin of dinosaurs was a
relatively rapid evolutionary event. Combined with our synthesis of
paleoecological data, we demonstrate there was little compositional
difference between the dinosaur precursor assemblages and the earliest
dinosaur assemblages, and thus, the initial appearance of dinosaurs
was not associated with a fundamental shift in ecosystem composition,
as classically stated.

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.

On Mon, Dec 7, 2015 at 12:38 PM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
> Lots of new stories on this item, but the official paper has still not
> been posted.
> Here are some of the news stories:
> http://unews.utah.edu/dinosaur-relatives-and-first-dinosaurs-more-closely-connected-than-previously-thought/
> http://phys.org/news/2015-12-dinosaur-relatives-dinosaurs-previously-thought.html
> https://www.sciencenews.org/article/new-dating-dino-ancestor-challenges-triassic-timeline
> http://www.nature.com/news/first-dinosaurs-arose-in-an-evolutionary-eye-blink-1.18953
> ***
> No link for now:
> C. Marsicano et al. The precise temporal calibration of dinosaur
> origins. Proceedings of the National Academy of Sciences. Published
> online December 7, 2015. doi: 10.1073/pnas.1512541112.