Abstract
The Mesozoic deposits of the Khorat Plateau in Thailand have yielded a rich but chronologically unclear record of dinosaur evolution. Here, we use detrital zircon U-Pb dating to establish precise ages for these deposits. The Nam Phong Formation, once thought to include some of the oldest sauropodomorphs, is now dated to the Pliensbachian stage of the Early Jurassic (ca. 190 Ma), at least 20 million years younger than previously assumed. The fauna of the Phu Kradung Formation, known for eusauropods and allosauroids, spans the Kimmeridgian to early Berriasian stages (ca. 155-140 Ma), covering the Late Jurassic to earliest Cretaceous. The diverse Sao Khua Formation dates to the Hauterivian–Barremian stages (ca. 130-120 Ma), while a shift to ornithischian-dominated communities occurs in the Aptian–Albian Khok Kruat Formation (ca. 120-100 Ma). This revised timeline shows that basal sauropodomorphs are significantly younger than assumed. It repositions Thai dinosaur assemblages within the global evolutionary framework, aligning their changes with faunal changes observed elsewhere and filling a critical gap in tropical fossil records.
Acknowledgements
We thank J. Longerey and J. Dauvier for assistance during zircon extraction at CEREGE, E. Gazquez for the conception of Figs. 1 and 4, and Mr. Sutham Wongchun, Chief of Phu Wiang National Park, as well as the Department of Mineral Resources of Thailand, for allowing sample collection and export.
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This research was funded by internal grants and is not associated with any external source of funding.
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Licht, A., Martin, J.E., Chanthasit, P. et al. A revised early Jurassic to Albian chronology for dinosaur evolution in tropical Asia. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-04096-5
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DOI: https://doi.org/10.1038/s43247-026-04096-5
Facts Only
* The Nam Phong Formation is dated to the Pliensbachian stage of the Early Jurassic (ca. 190 Ma).
* The fauna of the Phu Kradung Formation spans the Kimmeridgian to early Berriasian stages (ca. 155-140 Ma).
* The Sao Khua Formation dates to the Hauterivian–Barremian stages (ca. 130-120 Ma).
* The Aptian–Albian Khok Kruat Formation is dated to approximately 120-100 Ma, correlating with a shift to ornithischian-dominated communities.
* Basal sauropodomorphs are significantly younger than previously assumed based on the new timeline.
Executive Summary
Full Take
The process of recalibrating regional fossil timelines based on high-precision radiometric dating reveals how local biological patterns integrate into global evolutionary sequences. The key implication is that regional faunal shifts, such as the transition to ornithischian dominance in the Khok Kruat Formation, are now situated within a framework where basal sauropodomorphs evolved considerably later than previously mapped. This alignment suggests that the rate and timing of evolutionary diversification in tropical Asia must be re-evaluated against global benchmarks. The established pattern is one of necessary revision: existing regional interpretations served as useful placeholders, but precise chronometry forces a realignment with broader global faunal change, thereby filling a gap in understanding how tropical ecosystems mirrored global evolutionary dynamics during the Jurassic and Cretaceous. The uncertainty introduced by refining these ages highlights the ongoing challenge in correlating localized paleontology with macroevolutionary trends across disparate geographical regions.
Bridge Questions: If the revised timeline is accepted, what do contemporary models of Mesozoic environmental fluctuation suggest about the pace of sauropodomorph evolution in Southeast Asia? How might integrating this refined local data impact interpretations of dispersal routes and faunal exchange between tropical landmasses during this period? What other poorly constrained fossil assemblages exist that could serve as independent chronometers to test this new regional calibration?
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