Siamraptor provides a new glimpse at the early evolution of carcharodontosaurian dinosaurs

Fossils discovered in Thailand represent a new genus and species of predatory dinosaur, according to a study released October 9, 2019 in the open-access journal PLOS ONE by Duangsuda Chokchaloemwong of Nakhon Ratchasima Rajabhat University, Thailand and colleagues.

Carcharodontosaurs were a widespread and successful group of large predatory dinosaurs during the Jurassic and Cretaceous Periods and were important members of ecosystems on multiple continents. However, the fossil record of these animals is notably lacking from the Early Cretaceous of Asia, with no definite carcharodontosaurs known from Southeast Asia.

In this study, Chokchaloemwong and colleagues describe fossil material from the Khok Kruat geologic formation in Khorat, Thailand, dating to the Early Cretaceous. These fossils include remains of the skull, backbone, limbs, and hips of at least four individual dinosaurs, and morphological comparison with known species led the authors to identify these remains as belonging to a previously unknown genus and species of carcharodontosaur which they named Siamraptor suwati.

Phylogenetic analysis indicates that Siamraptor is a basal member of the carcharodontosaurs, meaning it represents a very early evolutionary split from the rest of the group. It is also the first definitive carcharodontosaur known from Southeast Asia, and combined with similarly-aged finds from Europe and Africa, it reveals that this group of dinosaurs had already spread to three continents by the Early Cretaceous.

The authors summarize their work as follows: "A Siam predator: New carnivorous dinosaur Siamraptor suwati discovered in Thailand.

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Citation: Chokchaloemwong D, Hattori S, Cuesta E, Jintasakul P, Shibata M, Azuma Y (2019) A new carcharodontosaurian theropod (Dinosauria: Saurischia) from the Lower Cretaceous of Thailand. PLoS ONE 14(10): e0222489. https:/ / doi. org/ 10. 1371/ journal. pone. 0222489

Funding: This work was supported by the Fukui Prefectural Government, Japan, and Nakhon Ratchasima Rajabhat University, Thailand. EC research was financed by a Postdoctoral Fellowship program of the Japan Society of Promotion of Science (JSPS) (Ref. PE18034). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.