| Siamodon Temporal range: Aptian ~ | |
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| Tooth of Siamodon nimngami | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Order: | † Ornithischia |
| Clade: | † Ornithopoda |
| Clade: | † Iguanodontia |
| Genus: | † Siamodon Buffetaut & Suteethorn, 2011 |
| Type species | |
| †Siamodon nimngami Buffetaut & Suteethorn, 2011 | |
Siamodon is an extinct genus of iguanodontian ornithopod dinosaur from Early Cretaceous deposits of northeastern Thailand. [1]
Siamodon is known from the holotype PRC-4, a well-preserved left maxilla and from the referred materials PRC-5, an isolated maxillary tooth and PRC-6, a braincase. It was collected in the Ban Saphan Hin site, Nakhon Ratchasima Province, from the Khok Kruat Formation, dating to the Aptian stage of the late Early Cretaceous, about 125-113 million years ago. [1]
Siamodon shows a combination of plesiomorphic and apomorphic features, including a maxilla shaped like an isosceles triangle, with the dorsal process located at about mid-length of the bone; a strong longitudinal bulge on the medial surface of the maxilla; at least 25 maxillary teeth, which bear a prominent median primary ridge, and one short weak subsidiary ridge or no subsidiary ridge at all, and mamillated denticles on the crown margins. The maxilla is 230 millimeters long, and has a height of 100 millimeters. The height of the isolated tooth is about 25-28 millimeters, and the width is about 14-17 millimeters. [1]
Siamodon differs from more basal iguanodontians, such as Iguanodon and closely related forms, in the morphology of its maxillary teeth, which are narrower and bear a strong median primary ridge, sometimes accompanied by a weak subsidiary ridge, instead of a distally displaced primary ridge and several subsidiary ridges, and the apex of the maxilla is in a more posterior position. Its maxilla differs from that of hadrosaurids in the articular area for the jugal, with forms a tab-like jugal process. Whereas in hadrosaurids, the expanded anterior end of the jugal contacts and overlaps a large sutural area on the maxilla. [1]
The combination of characters seen in the maxilla of Siamodon nimngami indicate that it belongs to a group of iguanodontians more derived than Iguanodon but basal to Hadrosauridae. It may be closely related to Probactrosaurus from China but they differ in the number of tooth positions. [1]
Siamodon was first named by Éric Buffetaut and Varavudh Suteethorn in 2011. The type species is Siamodon nimngami. The generic name is derived from Siam, the ancient name of Thailand; and odous, Greek for "tooth". The specific name is in honour of Witaya Nimngam, who donated the specimens to the authors. [1]
Ouranosaurus is a genus of herbivorous basal hadrosauriform dinosaur that lived during the Aptian stage of the Early Cretaceous of modern-day Niger and Cameroon. Ouranosaurus measured about 7–8.3 metres (23–27 ft) long and weighed 2.2 metric tons. Two rather complete fossils were found in the Elrhaz Formation, Gadoufaoua deposits, Agadez, Niger, in 1965 and 1970, with a third indeterminate specimen known from the Koum Formation of Cameroon. The animal was named in 1976 by French paleontologist Philippe Taquet; the type species being Ouranosaurus nigeriensis. The generic name is a combination of ourane, a word with multiple meanings, and sauros, the Greek word for lizard. The specific epithet nigeriensis alludes to Niger, its country of discovery. And so, Ouranosaurus nigeriensis could be interpreted as "brave lizard originating from Niger".
Siamotyrannus is a genus of theropod dinosaur from the early Cretaceous of Thailand.
Iguanodontidae is a family of iguanodontians belonging to Styracosterna, a derived clade within Ankylopollexia.
Siamosaurus is a genus of spinosaurid dinosaur that lived in what is now known as China and 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 only 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.
Kinnareemimus is a genus of ornithomimosaurian theropod dinosaur from Thailand. It is known only from incomplete remains discovered no later than the early 1990s that includes vertebrae, partial pubic bones, metatarsals, and an incomplete fibula. The third metatarsal exhibits a distinctive lateral "pinching", known as the "arctometarsalian" condition, variations of which are found in ornithomimosaurs, tyrannosauroids, troodontids, and caenagnathids. Its remains were collected from the Early Cretaceous Sao Khua Formation, dating to the Barremian stage, at Phu Wiang, Khon Kaen Province. Its early occurrence makes it among the earliest ornithomimosaur known, depending on the age of the formation. Buffetaut et al. suggest the fossils of Kinnareemimus may indicate an Asian origin for advanced ornithomimosaurs.
Phuwiangosaurus is a genus of titanosaur dinosaur from the Early Cretaceous (Valanginian-Hauterivian) Sao Khua Formation of Thailand. The type species, P. sirindhornae, was described by Martin, Buffetaut, and Suteethorn in a 1993 press release and was formally named in 1994. The species was named to honor Princess Maha Chakri Sirindhorn of Thailand, who was interested in the geology and palaeontology of Thailand, while the genus was named after the Phu Wiang area, where the fossil was discovered.
Rhabdodontidae is a family of herbivorous iguanodontian ornithopod dinosaurs whose earliest stem members appeared in the middle of the Lower Cretaceous. The oldest dated fossils of these stem members were found in the Barremian Castrillo de la Reina Formation of Spain, dating to approximately 129.4 to 125.0 million years ago. With their deep skulls and jaws, Rhabdodontids were similar to large, robust iguanodonts. The family was first proposed by David B. Weishampel and colleagues in 2003. Rhabdodontid fossils have been mainly found in Europe in formations dating to the Late Cretaceous.
The Sao Khua Formation is a middle member of the Khorat Group. It consists of an alteration of pale red to yellowish-gray, fine to medium-grained sandstone and grayish-reddish brown siltstone and clay. Rare pale red to light gray conglomerates, containing carbonate pebbles, are also characteristic of this formation. This geological formation in Thailand dates to the Early Cretaceous age, specifically the Valanginian through Hauterivian stages.
The Early Cretaceous Phu Kradung Formation is the lowest member of the Mesozoic Khorat Group which outcrops on the Khorat Plateau in Isan, Thailand. This geological formation consists of micaceous, brown to reddish-brown siltstone beds with minor brown and grey shale and sandstone beds. Occasional lime-noduled conglomerate occurs.
Iguanacolossus is a genus of iguanodontian ornithopod dinosaur that lived in North America during the Early Cretaceous period. It is known from UMNH VP 20205, the associated holotype with a large partial skeleton of a single individual.
The Khok Kruat Formation is a rock formation found in northeastern Thailand. It is the uppermost formation of the Khorat Group. It is dated to the Aptian stage of the Early Cretaceous period, and is notable for its fossils of dinosaurs. It is equivalent to the Gres superieurs Formation of Laos. The group is a fluvial formation consisting primarily of red siltstones and sandstones.
Ratchasimasaurus is a genus of iguanodontian ornithopod dinosaur from Early Cretaceous Khok Kruat Formation of Nakhon Ratchasima Province in northeastern Thailand. The type and only species is R. suranareae, named after Thao Suranari, a 19th-century war heroine. It was considered by one study to be a nomen dubium, diagnosed with characters widespread in Styracosterna.
Ichthyovenator is a genus of spinosaurid dinosaur that lived in what is now Laos, sometime between 125 and 113 million years ago, during the Aptian stage of the Early Cretaceous period. It is known from fossils collected from the Grès supérieurs Formation of the Savannakhet Basin, the first of which were found in 2010, consisting of a partial skeleton without the skull or limbs. This specimen became the holotype of the new genus and species Ichthyovenator laosensis, and was described by palaeontologist Ronan Allain and colleagues in 2012. The generic name, meaning "fish hunter", refers to its assumed piscivorous lifestyle, while the specific name alludes to the country of Laos. In 2014, it was announced that more remains from the dig site had been recovered; these fossils included teeth, more vertebrae (backbones) and a pubic bone from the same individual.
Zhanghenglong is an extinct genus of herbivorous hadrosauroid iguanodont dinosaur known from the Late Cretaceous Majiacun Formation in Xixia County of Henan Province, China. It contains a single species, Zhanghenglong yangchengensis, represented by a disarticulated and partial cranium and postcranial skeleton.
Sirindhorna is a genus of hadrosauroid ornithopod dinosaur from Early Cretaceous deposits of northeastern Thailand.
Matheronodon is a genus of rhabdodontid ornithopod dinosaur from the late Cretaceous Period of the Grès à Reptiles Formation in France. The genus contains a single species, M. provincialis, which is known from a single maxilla and associated teeth. It was named by Pascal Godefroit and colleagues in 2017. The teeth of Matheronodon are large but few in number. The teeth are also in an unusual arrangement, emerging alternatingly from one of a pair of fused tooth sockets in its mouth. In life, the teeth would have functioned like a pair of scissors, allowing Matheronodon to feed on the tough leaves of monocot plants.
Varavudh Suteethorn, or Warawut Suteethorn is a Thai geologist and palaeontologist. He is the current director of the Palaeontological Research and Education Centre, Mahasarakham University. He is best known for his work on vertebrate palaeontology in northeastern Thailand, having contributed to the discovery of many fossil taxa and dig sites in the Khorat Plateau, as a part of a long-standing collaboration between Thai and French scientists.
Siamraptor is an extinct genus of carcharodontosaurian dinosaur, containing the single species S. suwati, known from the Khok Kruat Formation of Thailand. It is the first definitive named carcharodontosaurian species known from Southeast Asia.
Acrorhizodus is an extinct genus of hybodont shark currently containing only the species: Acrorhizodus khoratensis. It is known from the Albian to Aptian aged Khok Kruat formation of the Khok Pha Suam locality near the town of Sri Muang Mai, Thailand. It displays a mix of features which sets it apart from all hybodont families currently known.
Brighstoneus is a genus of hadrosauriform dinosaur from the Early Cretaceous Wessex Formation of the Isle of Wight, England. The genus contains a single species, Brighstoneus simmondsi, known from a partial skeleton.
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