Open Paleo

Siamosaurus

Buffetaut & Ingavat, 1986 sie-AM-o-SAWR-us Nomen dubium

Named for Siam, the ancient name of Thailand, where the fossils were found, combined with Greek 'sauros' meaning 'lizard'; meaning 'Siam lizard.'

137.1–125.8 million years ago Valanginian–Hauterivian, Early Cretaceous
Early Cretaceous stages

Siamosaurus is a potentially dubious genus of spinosaurid dinosaur that lived in what is now Thailand and possibly China during the Early Cretaceous period (Barremian to Aptian) and is the first reported spinosaurid from Asia. It is confidently known only from tooth fossils; the first were found in the Sao Khua Formation, with more teeth later recovered from the younger Khok Kruat Formation. The only species Siamosaurus suteethorni, whose name honors Thai paleontologist Varavudh Suteethorn, was formally described in 1986. In 2009, four teeth from China previously attributed to a pliosaur — under the species "Sinopliosaurus" fusuiensis — were identified as those of a spinosaurid, possibly Siamosaurus. It is yet to be determined if two partial spinosaurid skeletons from Thailand and an isolated tooth from Japan also belong to Siamosaurus.

Under dispute

Siamosaurus suteethorni is based solely on isolated teeth, and both its affinities and its validity have been contested. Buffetaut and Ingavat (1986) tentatively referred it to Spinosauridae, but Sues and colleagues (2002) considered the material insufficient to establish even dinosaurian affinities, and Weishampel and colleagues (2004) placed it no more precisely than Theropoda indeterminate. Its spinosaurid identity has since gained support: Buffetaut and colleagues (2008) cited converging lines of evidence — including a spinosaurid skeleton from the tooth-bearing Khok Kruat Formation — and Carrano and colleagues (2012) referred the teeth to ?Spinosauridae. Nonetheless the genus is widely treated as a nomen dubium, because its teeth cannot be distinguished from those of other spinosaurids (Holtz and colleagues, 2004; Sales and Schultz, 2017; Smyth and colleagues, 2020); associated skeletal material may eventually permit a more secure identification.

Species

Siamosaurus suteethorni Buffetaut & Ingavat, 1986 Nomen dubium

Type species

Named for Thai geologist and paleontologist Varavudh Suteethorn, in recognition of contributions to vertebrate paleontology discoveries in Thailand.

Holotype
DMR TF 2043a , Department of Mineral Resources
Material
A single well-preserved tooth crown.
Notes
Eight further teeth (DMR TF 2043b–i) from the same locality are paratypes.
Horizon
Sao Khua Formation, Valanginian–Hauterivian, Early Cretaceous , 137.1–125.8 million years ago
Locality
Phu Wiang, Khon Kaen, Thailand

References

  1. Buffetaut, E.; Ingavat, R. (1986). Unusual theropod teeth from the Upper Jurassic of Phu Wiang, northeastern Thailand. Revue de Paléobiologie 5(2): 217-220.

    Erected Siamosaurus suteethorni on isolated teeth and tentatively referred it to Spinosauridae.

    buffetaut1986a
  2. Sues, H. D.; Frey, E.; Martill, D. M.; Scott, D. M. (2002). Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology 22(3): 535-547. Informa UK Limited. doi:10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2

    Considered the available material insufficient to establish even dinosaurian affinities for Siamosaurus.

    sues2002a
  3. Holtz, T. R.; Molnar, R. E.; Currie, P. J. (2004). Basal Tetanurae. The Dinosauria, Second Edition (Weishampel, D. B.; Dodson, P.; Osmólska, H., eds.) 71-110. University of California Press, Berkeley.

    Listed Siamosaurus suteethorni among nomina dubia based on isolated teeth.

    holtz2004a
  4. Weishampel, D. B.; Dodson, P.; Osmólska, H. (eds.) (2004). The Dinosauria, Second Edition. University of California Press, Berkeley.

    Placed Siamosaurus no more precisely than Theropoda indeterminate.

    weishampel2004a
  5. Buffetaut, E.; Suteethorn, V.; Tong, H.; Amiot, R. (2008). An Early Cretaceous spinosaur theropod from southern China. Geological Magazine 145(5): 745-748. doi:10.1017/S0016756808005360

    Argued from converging evidence, including a spinosaurid skeleton in the tooth-bearing Khok Kruat Formation, that Siamosaurus is a spinosaurid.

    buffetaut2008a
  6. Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. (2012). The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology 10(2): 211-300. Informa UK Limited. doi:10.1080/14772019.2011.630927

    Referred the teeth to ?Spinosauridae, finding too little material to support retention of the taxon pending associated skeletal remains.

    carrano2012a
  7. Sales, M. A. F.; Schultz, C. L. (2017). Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil. PLOS ONE 12(11): e0187070. doi:10.1371/journal.pone.0187070

    Treated Siamosaurus as a nomen dubium whose teeth cannot be distinguished from those of other Cretaceous spinosaurids.

    sales2017a
  8. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Reports Siamosaurus as widely considered a nomen dubium.

    jones2026c
  9. Smyth, R. S. H.; Ibrahim, N.; Martill, D. M. (2020). Sigilmassasaurus is Spinosaurus: a reappraisal of African spinosaurines. Cretaceous Research 114: 104520. Elsevier BV. doi:10.1016/j.cretres.2020.104520

    Treated Siamosaurus suteethorni as a nomen dubium.

    smyth2020a