Siamodon
Named after Siam (the historical name for Thailand) where it was found, combined with Greek odon, "tooth" — derived from the country of origin
Siamodon is an extinct genus of iguanodontian ornithopod dinosaur from Early Cretaceous deposits of northeastern Thailand.
Under dispute
Siamodon nimngami was named for a maxilla from the Khok Kruat Formation and compared most closely with Probactrosaurus among advanced iguanodontians (Buffetaut and Suteethorn, 2011). Norman (2015) finds no autapomorphies in its diagnosis, treats it as a nomen dubium until more material is described, and suggests it may belong to Ratchasimasaurus, from the same formation; Poole (2022) notes that the two were named on non-overlapping material. In the one analysis that resolves it, it falls in a polytomy at the base of Hadrosauriformes, outside Hadrosauroidea (Madzia and colleagues, 2019).
Diagnosis
- Maxilla shaped like isosceles triangle with dorsal process located at approximately mid-length of bone
- Tab-like jugal process on lateral maxillary surface
- Strong longitudinal bulge on medial surface of maxilla, forming prominent shelf-like ridge anteriorly
- At least 25 maxillary teeth bearing prominent median primary ridge with weak or absent subsidiary ridges
- Mamillated denticles on crown margins of maxillary teeth
Species
Siamodon nimngami Buffetaut & Suteethorn, 2011 Disputed
Type species
Named for Witaya Nimngam, who donated the fossil specimens to the describing authors.
- Holotype
- PRC-4 , Paleontological Research and Education Centre, Maha Sarakham University
- Material
- Nearly complete left maxilla bearing several teeth. Approximately 430 mm long, 100 mm maximum height. Triangular outline with dorsal process at mid-length. Tooth row shows at least 25 tooth positions. Strong longitudinal bulge on medial surface.
- Horizon
- Khok Kruat Formation, Aptian, Early Cretaceous , 121.4–113.2 million years ago
- Locality
- Ban Saphan Hin, Nakhon Ratchasima, Thailand Shibata and colleagues (2015) record that Jintasakul, a co-author, holds the site to be Ban Nong Rangka in the adjacent subdistrict rather than Ban Saphan Hin.
References
-
Buffetaut, E.; Suteethorn, V. (2011). A new iguanodontian dinosaur from the Khok Kruat Formation (Early Cretaceous, Aptian) of northeastern Thailand. Annales de Paléontologie 97(1-2): 51-62. Elsevier BV. doi:10.1016/j.annpal.2011.08.001
Named Siamodon for a maxilla and compared it most closely with Probactrosaurus.
buffetaut2011a -
Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.
Source of the body length estimate.
jones2026a -
Norman, D. B. (2015). On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna). Zoological Journal of the Linnean Society 173: 92-189. doi:10.1111/zoj.12193
Considered Siamodon a nomen dubium pending more material, possibly referable to Ratchasimasaurus.
norman2015a -
Shibata, M.; Jintasakul, P.; Azuma, Y.; You, H. L. (2015). A New Basal Hadrosauroid Dinosaur from the Lower Cretaceous Khok Kruat Formation in Nakhon Ratchasima Province, Northeastern Thailand. PLOS ONE 10(12): e0145904. Public Library of Science (PLoS). doi:10.1371/journal.pone.0145904
Records a co-author's dispute over the type locality, holding it to be Ban Nong Rangka rather than Ban Saphan Hin.
shibata2015a -
Madzia, D.; Jagt, J. W. M.; Mulder, E. W. A. (2019). Osteology, phylogenetic affinities and taxonomic status of the enigmatic late Maastrichtian ornithopod taxon Orthomerus dolloi (Dinosauria, Ornithischia). Cretaceous Research 108: 104334. Elsevier BV. doi:10.1016/j.cretres.2019.104334
Recovered Siamodon in a polytomy at the base of Hadrosauriformes, outside Hadrosauroidea.
madzia2019a -
Poole, K. E. (2022). Phylogeny of iguanodontian dinosaurs and the evolution of quadrupedality. Palaeontologia Electronica 25(3): a30. doi:10.26879/702
Excluded Siamodon and Ratchasimasaurus as fragmentary, noting that they were named on non-overlapping material.
poole2022a