Dinosaur fauna from the Lower Cretaceous of Phu Kao-Phu Phan Kham, northeastern Thailand: a review and update

Phu Kao-Phu Phan Kham Mountain ranges, situated on the border of Nong Bua Lamphu, Udon Thani, and Khon Kaen provinces, northeastern Thailand, bear several localities that yield dinosaurs and other vertebrate faunas in the Lower Cretaceous. However, this area has received relatively little attention from the scientific community and the public. Here we review and report new dinosaur materials recovered from this region, some found decades ago, others discovered recently. We identify and discuss their taxonomy and paleobiodiversity. In the Barremian Sao Khua Formation, theropod dinosaurs were represented by spinosaurids, an early branching megaraptoran, a large indeterminate theropod, and small indeterminate theropods. Sauropods were represented by an indeterminate sauropod, a neosauropod, and titanosauriforms, including probable brachiosaurid and non-titanosaur somphospondylans. Other vertebrate groups, including crocodilians, turtles, fishes, and sharks, indicate a similar composition to other Sao Khua Formation communities in northeastern Thailand. The Sao Khua vertebrate assemblage exhibits the taxonomic diversity of dinosaur fauna and is currently the best-documented assemblage in the Early Cretaceous of Southeast Asia. The Aptian–Albian Khok Kruat Formation, however, yields less diverse vertebrates. They are represented by freshwater sharks, crocodilians, and spinosaurid theropods. This may be due to sampling bias, environmental, or taphonomic conditions. This study provides the basis for future paleontological exploration and research of Mesozoic vertebrates in northeastern Thailand.