Age, depositional history, and paleoclimatic setting of Early Cretaceous dinosaur assemblages from the Sao Khua Formation (Khorat Group), Thailand

Ornithischian dinosaurs in Southeast Asia: a review with palaeobiogeographic implications

“…Amongst the thousands of saurischian bones that have been collected from north-eastern Thailand, no evidence of ornithischians has yet been found in this formation (Buffetaut et al 2015). The lack of ornithischians in the Sao Khua Formation is possibly consistent with the ecological composition of Valanginian/Hauterivian aged assemblages from Gondwana, for example, the "wood beds" of the upper Kirkwood Formation of South Africa and the Bajada Colorado Formation of South America, which are dominated by various-sized theropods and multiple cohabiting species of sauropods (Tucker et al 2022). This is in contrast to those pre-Barremian dinosaur assemblages of Laurasian landmasses from Europe and North America, which have a diverse ornithischian record including ankylosaurians and iguanodontians and which shared habitats with other sauropod and theropod dinosaurs (Norman 2010;Kirkland et al 2016;Tucker et al 2022).…”

“…In the most recent publications, Sao Khua vertebrate fauna, including turtles and theropod dinosaurs, are considered to be Barremian (Samathi et al 2019b;Tong et al 2019a), and following a more refined regional biostratigraphic correlation of the freshwater bivalves Pseudohyria (Matsumotoina) matsumotoi suggesting a late Barremian age (Tumpeesuwan et al 2010). Lastly, the radiometric data on detrital zircon grains indicated a tightly restricted late Valanginian-early Hauterivian age (133.6-132.1 Ma) for the Sao Khua Formation, and establishes that the dinosaur fauna is ~ 5-9 million years older than currently known (Tucker et al 2022).…”

“…This Formation was dated as Lower Cretaceous (Berriasian-Early Barremian) from a rich palynological assemblage (Racey 2009;Racey and Goodall 2009). However, a subsequent study using radiometric dating on detrital zircon grains suggested that the dates for the underlying Sao Khua Formation are much older than previously suspected (Tucker et al 2022). The study restricted the upper part of the Sao Khua Formation to no earlier than early Hauterivian, which means that the Phra Wihan Formation is likely not younger than Valanginian in age (Tucker et al 2022).…”

“…This is in contrast to those pre-Barremian dinosaur assemblages of Laurasian landmasses from Europe and North America, which have a diverse ornithischian record including ankylosaurians and iguanodontians and which shared habitats with other sauropod and theropod dinosaurs (Norman 2010;Kirkland et al 2016;Tucker et al 2022). By comparison with contemporaneous formations in Asia, ornithischian remains are still somewhat limited (Tucker et al 2022). Material of an indeterminate stegosaurian has been reported from the Mengyin Formation (Berriasian-Valanginian), Shandong Province of China (Tucker et al 2022).…”

“…By comparison with contemporaneous formations in Asia, ornithischian remains are still somewhat limited (Tucker et al 2022). Material of an indeterminate stegosaurian has been reported from the Mengyin Formation (Berriasian-Valanginian), Shandong Province of China (Tucker et al 2022). A stegosaurine Wuerhosaurus homheni and probable basal ceratopsians have been reported from the Lianmuqin Formation (?Valanginian) of Tugulu Group, Xinjiang Region of China (Sereno and Shichin 1988;Maidment et al 2008).…”