Isolated theropod teeth from the Upper Jurassic to Lower Cretaceous Khorat Group: Implications for theropod diversity in Thailand

Isolated theropod teeth are notably abundant of vertebrate remains within the Upper Jurassic to Lower Cretaceous Khorat Group of Thailand. However, despite the discovery of numerous dental materials, only a limited number of studies have focused on the morphology and taxonomy of these isolated teeth. This study investigated 112 isolated theropod teeth were retrieved from 19 localities on the Khorat Plateau in Northeastern Thailand. These teeth were divided into five morphotypes based on dental characteristics. They were identified based on cladistic and discriminant analyses that recovered four clades of theropod dinosaurs: Metriacanthosauridae, Tyrannosauroidea, Spinosauridae, and Allosauria. This dental evidence provide significant insights into the theropod diversity in Thailand during the Late Jurassic to Early Cretaceous. Specifically, the Late Jurassic to Early Cretaceous Phu Kradung Formation revealed an extended presence of metriacanthosaurids and basal tyrannosauroids, while the Sao Khua and Khok Kruat Formations indicated a shift towards allosaurian and spinosaurid dominance during the Early Cretaceous. The absence of metriacanthosaurids and basal tyrannosauroids in later formations suggests a faunal turnover, with allosaurians and spinosaurids becoming more prevalent, aligning with the changes in theropod faunal composition across Eurasia. Furthermore, this contribution suggested the faunal turnover pattern in the Eurasian theropods during the Jurassic-Cretaceous boundary interval, which might have been related to the change in herbivorous dinosaurs during this crucial timeframe of dinosaur evolution.