A revised early Jurassic to Albian chronology for dinosaur evolution in tropical Asia

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. Sauropodomorph-bearing assemblages from the Khorat Plateau, Thailand, begin at least 20 million years later than previously believed, with subsequent faunal turnover paralleling that observed in Laurasia and Gondwana, according to detrital zircon U–Pb dating.