Abstract Phosphatic remains (tooth enamel, turtle shell fragments and fish scales) of continental vertebrates (freshwater fish, crocodilians, turtles, and theropod and sauropod dinosaurs) recovered from eight localities of NE Thailand ranging in age from the Late Jurassic to the late Early Cretaceous have been analysed for their oxygen isotopic compositions (δ 18 O p ). From these preliminary data, local meteoric water δ 18 O w values estimated using δ 18 O p values of crocodilians and turtles range from −4.1±2‰ at the end of the Jurassic to −8.3±2‰ during the Early Cretaceous, suggesting a transition from dry to wetter climates with increasing amount of seasonal precipitation from several hundred millimetres per year to several thousand millimetres. Measurable offsets in δ 18 O p values observed between dinosaur taxa (the spinosaurid theropod Siamosaurus , other theropods and nemegtosaurid sauropods) are interpreted in terms of differences in water strategies, and suggest that Siamosaurus had habits similar to those of semi-aquatic vertebrates such as crocodilians or freshwater turtles.