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. 2016 Jan 19;113(3):509-13.
doi: 10.1073/pnas.1512541112. Epub 2015 Dec 7.

The precise temporal calibration of dinosaur origins

Claudia A Marsicano  1 , Randall B Irmis  2 , Adriana C Mancuso  3 , Roland Mundil  4 , Farid Chemale  5
Affiliations

The precise temporal calibration of dinosaur origins

Claudia A Marsicano et al. Proc Natl Acad Sci U S A. .

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.

Keywords: Chañares Formation; Triassic; biostratigraphy; dinosaur origins; geochronology.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Geological map of the Chañares–Gualo area in Talampaya National Park (La Rioja Province). The main fossiliferous localities are the Romer locality and Río Gualo. The latter locality is where the detailed section (SI Appendix) was measured. (Right) Generalized stratigraphic column from Río Gualo showing the sampled levels. For additional references, see SI Appendix.
Fig. 2.
Fig. 2.
ID-TIMS U–Pb single-zircon analyses for samples RBI12/CN-R7 (light gray/blue) and ZR11 (dark gray/red). Panels show concordia plot (Left) and age-ranked representation (Right), including age interpretation considering the youngest age of each sample as maximum depositional age. Data and further discussion of these analyses can be found in SI Appendix.
Fig. 3.
Fig. 3.
The record of early dinosauromorph evolution in the Ischigualasto–Villa Union Basin as calibrated by biostratigraphically independent geochronology. Relative abundance of specimens and relative richness of species for the tetrapod clades Synapsida, Archosauriformes (including Dinosauromorpha), Dinosauromorpha (including Dinosauria), and Dinosauria are plotted vs. time in millions of years. The Exaeretodon biozone of the upper Ischigualasto Formation is excluded from these plots because of its low sample size, poor sampling, and taphonomic biases against vertebrate preservation (data sources in SI Appendix).
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Comment in

  • Dating the origin of dinosaurs.
    Sues HD. Sues HD. Proc Natl Acad Sci U S A. 2016 Jan 19;113(3):480-1. doi: 10.1073/pnas.1523058113. Epub 2016 Jan 8. Proc Natl Acad Sci U S A. 2016. PMID: 26747603 Free PMC article. No abstract available.

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