page_title: Siamosaurus
section_title: Classification
hierarchical_section_title: Siamosaurus / Classification
caption_attribution_description: English: Rigorous life reconstruction of the spinosaurid theropod Ichthyovenator laosensis. References: Fossil material: Allain et al. (2012).[1] National Museum of Nature and Science, Tokyo.File:Ichthyovenator_laosensis.jpgFile:Ichthyovenator_vertebrae.jpg[2] Muséum national d'Histoire naturelle, Paris.File:Ichthyovenator_laosensis_65849.jpg Tail fin: Muséum national d'Histoire naturelle, Paris.File:Ichthyovenator_laosensis_65849.jpg Arden et al. (2018).[3] Allain (pers. comm.). Basis for spinosaurine classification and resulting inferences: Allain et al. (2014).[4] Arden et al. (2018).[5] Head based on Irritator challengeri, "Angaturama", Oxalaia quilombensis, and Spinosaurus aegyptiacus: Sales and Schultz (2017).[6] Ibrahim et al. (2020).[7]" Hands and arms based on "Angaturama", Suchomimus tenerensis, and Baryonyx walkeri: Aureliano et al. (2018).[8] Francisco Bruñén (2018).[9] Scott Hartman (2018).[10] Torso, legs, and missing sail and tail anatomy based on Spinosaurus aegyptiacus, Romualdo Formation Spinosaurinae, and Suchomimus tenerensis: Ibrahim et al. (2020).[11]" Aureliano et al. (2018).[12] Francisco Bruñén (2018).[13] Feet based on Spinosaurus aegyptiacus and Portuguese Spinosauridae indet. tracks: Ibrahim et al. (2014) (supplementary materials).[14] Casanovas et al. (1993)[15] Throat pouch/dewlap based on those seen in living aquatic dinosaurs and crocodilians: Pelecanus conspicillatus (Australian pelicans):File:Australian_Pelican_showing_large_pouch.jpg Alligator mississippiensis (American alligators):[16] Speculative colouration based on living aquatic (and some terrestrial) dinosaurs, as well as other animals with similar semiaquatic or marine lifestyles, including: Upupa epops (hoopoes):[17] Aptenodytes forsteri (emperor penguins):File:Aptenodytes_forsteri_-Snow_Hill_Island,_Antarctica_-adults_and_juvenile-8.jpg Carcharhinus melanopterus (blacktip reef sharks):File:Carcharhinus_melanopterus_bora_bora.png Paleosuchus trigonatus (smooth-fronted caimans):File:Paleosuchus-trigonatus.jpg Lophodytes cucullatus (hooded mergansers):File:Hooded_Merganser_(Lophodytes_cucullatus)_(1).JPG Branta ruficollis (red-breasted geese):File:Red-breasted_goose_arp.jpg
context_page_description: Siamosaurus is a genus of spinosaurid dinosaur that lived in what is now Thailand during the Early Cretaceous period 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 type species Siamosaurus suteethorni, whose name honours Thai palaeontologist 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.
  Since it is based only on teeth, Siamosaurus' body size is uncertain, though it has been estimated at between 5.1 to 9.1 metres in length. The holotype tooth is 62.5 millimetres long. Siamosaurus' teeth were straight, oval to circular in cross section, and lined with distinct lengthwise grooves. Its teeth had wrinkled enamel, similar to teeth from the related genus Baryonyx.
context_section_description: In 1986, Buffetaut and Ingavat classified Siamosaurus as a theropod because of the straight tall crown and double sideways recurvature of its teeth. At the time, Siamosaurus' particular combination of dental characteristics, especially the longitudinal fluting and lack of serrations, had not been observed in other theropods. The authors noted similarities in Siamosaurus' teeth to those of ceratosaurian tooth crowns, some of which also have longitudinal flutes. However, this identification was ruled out, since ceratosaur teeth are more narrow and blade-like in cross section, bear far fewer dental flutes, and have distinct serrations. Buffetaut and Suteethorn concluded that the closest taxon in dentition to Siamosaurus was Spinosaurus aegyptiacus from Egypt, whose fragmentary fossils had been destroyed during World War II. Like Siamosaurus, this African taxon had straight and unserrated conical teeth. Though Spinosaurus lacked the developed flutes seen in Siamosaurus, Buffetaut and Ingavat noted that both smooth and fluted spinosaur teeth have been reported from Africa. Therefore, they tentatively placed Siamosaurus in the family Spinosauridae, based on the close similarities in dentition to S. aegyptiacus.
  Many palaeontologists later questioned Buffetaut and Ingavat's identification of Siamosaurus, given that spinosaurid teeth, including many from Asia, have often been mistaken for those of aquatic reptiles like crocodilians, plesiosaurs, and ichthyosaurs. In view of this, the German palaeontologist Hans-Dieter Sues and colleagues in 2002 asserted that there is not enough material to confidently identify Siamosaurus as a dinosaur. In 2004, American palaeontologist Thomas Holtz and colleagues considered it a dubious name, stating that the teeth might instead belong to a contemporaneous fish such as a saurodontid or an ichthyodectid teleost. The same year, American palaeontologist David Weishampel and colleagues considered Siamosaurus an indeterminate theropod. In 2012, an analysis by American palaeontologist Matthew Carrano and colleagues agreed with the possibility of confusion with other reptiles, and regarded the genus as a possible indeterminate spinosaurid. They noted that oftentimes, isolated teeth are an unstable foundation for naming new theropod taxa, and most species based on them turn out to be invalid. This problem is especially common with spinosaurids, given that skull and skeletal fossils from the group are rare.
  Authors such as Buffetaut and Ingavat in 1986, and Hasegawa and colleagues in 2003, have noted that since crocodilian teeth are usually more strongly recurved than spinosaur teeth, they can be distinguished from each other. Crocodilians also lack the lateral double recurvature of Siamosaurus' tooth crowns, which, based on their shape, were vertically inserted into the jaw, whereas long-snouted crocodilian teeth are usually angled outwards from the mouth. Though Siamosaurus and plesiosaur teeth are similar in overall shape, Buffetaut and Ingavat pointed out that plesiosaur teeth were significantly more recurved. Other researchers also noted that compared to plesiosaurs, Asian spinosaurid teeth also have coarser and more numerous flutes that extend almost the whole length of the crown. In 2008, Buffetaut and colleagues stated that the "S." fusuiensis teeth bear carinae on the plane of the crown's curvature, a condition not observed in plesiosaur teeth. The discovery of the Khok Kruat skeleton and of baryonychine teeth with dental flutes similar to those of Siamosaurus, were also brought up by the researchers as further evidence of Siamosaurus' spinosaurid classification. Later discoveries revealed that largely straight tooth crowns with flutes and a lack or reduction of serrations were unique characteristics of spinosaurid teeth.
  In 2014, Italian palaeontologist Federico Fanti and colleagues considered the various spinosaurid teeth from East Asia, including those of S. suteethorni, as identical to those of Spinosaurus. In 2017, Brazilian palaeontologists Marcos Sales and Cesar Schultz suggested that t
caption: Restoration of Ichthyovenator, a spinosaurine from what is now Laos and one of the closest known relatives of Siamosaurus.[38]
exif: {}