The precise temporal calibration of dinosaur origins

MARSICANO, CLAUDIA; IRMIS, RANDALL; MANCUSO, ADRIANA; MUNDIL, ROLAND; CHEMALE, FARID

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Lugar: Washington DC, USA; Año: 2016

0027-8424

Dinosaurs have been major components of ecosystems for over 200million years. Although different macroevolutionary scenarios existto explain the Triassic origin and subsequent rise to dominance ofdinosaurs and their closest relatives (dinosauromorphs), all lack criticalsupport from a precise biostratigraphically independent temporalframework. The absence of robust geochronologic age control forcomparing alternative scenarios makes it impossible to determine ifobserved faunal differences vary across time, space, or a combinationof both. To better constrain the origin of dinosaurs, we producedradioisotopic ages for the Argentinian Chañares Formation, whichpreserves a quintessential assemblage of dinosaurian precursors(early dinosauromorphs) just before the first dinosaurs. Our newhigh-precision chemical abrasion thermal ionization mass spectrometry(CA-TIMS) U?Pb zircon ages reveal that the assemblage is earlyCarnian (early Late Triassic), 5- to 10-Ma younger than previouslythought. Combined with other geochronologic data from the samebasin, we constrain the rate of dinosaur origins, demonstrating theirrelatively rapid origin in a less than 5-Ma interval, thus halving thetemporal gap between assemblages containing only dinosaur precursorsand those with early dinosaurs. After their origin, dinosaurs onlygradually dominated mid- to high-latitude terrestrial ecosystems millionsof years later, closer to the Triassic?Jurassic boundary.