Sao Khua Formation, where the first Siamosaurus fossils were discovered, is part of the Khorat Group. The formation is dated to the Barremian stage of the Early Cretaceous period, 129.4 to 125 million years ago. In 1983, French palaeontologist Éric Buffetaut and his Thai colleague Rucha Ingavat described a set of fossil teeth recovered from the Phu Pratu Teema locality of the Sao Khua Formation, in the Phu Wiang area of Khon Kaen Province. They did not conclude as to what animal they originated from, their opinion being that the specimens belonged "either to an unusual theropod dinosaur or to some unknown crocodilian". In 1986, a reassessment of the remains by the same authors attributed them to a new genus and species of spinosaurid theropod, which they named Siamosaurus suteethorni. The generic name alludes to the ancient name of Thailand, "Siam", and is combined with the Ancient Greek word (), meaning "lizard" or "reptile". The specific name honours Thai geologist and palaeontologist Varavudh Suteethorn, and his contributions to vertebrate palaeontology discoveries in Thailand. The best-preserved specimen from the teeth described, designated DMR TF 2043a, was chosen as the holotype of Siamosaurus. The paratypes comprise eight other well-preserved teeth catalogued as DMR TF 2043b to i. The original fossils are currently housed in the palaeontological collection of the Department of Mineral Resources, Bangkok. Siamosaurus teeth are common in the Sao Khua Formation, and further isolated specimens were found later throughout the late 20th and early 21st centuries. Sculptures of the animal have been erected in various places across northeastern Thailand, including Si Wiang Dinosaur Park, the Siam Paragon shopping mall in Bangkok, the Phu Wiang Dinosaur Museum, and the Sirindhorn Museum. S. suteethorni was also illustrated on Thai postage stamps released in 1997, along with fellow Thai dinosaurs Phuwiangosaurus sirindhornae, Siamotyrannus isanensis, and Psittacosaurus sattayaraki. Thailand's Khok Kruat Formation is dated to the Aptian age (between 125 and 113 million years ago), younger than the Sao Khua Formation. The Khok Kruat Formation has provided many spinosaurid teeth, including ones from Siamosaurus and closely allied forms. Given the varied size and morphology of the teeth found, the presence of multiple spinosaur taxa in the region is likely. Nearly 60 fossil teeth were recovered from the formation during fieldwork by Thai-French palaeontological teams between 2003 and 2008, including specimens from the Sam Ran, Khok Pha Suam, and Lam Pao Dam localities. Eight of