Siamodon

Siamodon is an extinct genus of iguanodontian ornithopod dinosaur from Early Cretaceous deposits of northeastern Thailand.[1]

Siamodon
Temporal range: Early Cretaceous, Aptian
Siamodon tooth1
Tooth of Siamodon nimngami
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Suborder: Ornithopoda
Clade: Iguanodontia
Genus: Siamodon
Buffetaut & Suteethorn, 2011
Type species
Siamodon nimngami
Buffetaut & Suteethorn, 2011

Discovery

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]

Description

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]

Etymology

Siamodon was first named by Eric 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]

References

  1. ^ a b c d e f Eric Buffetaut and Varavudh Suteethorn (2011). "A new iguanodontian dinosaur from the Khok Kruat Formation (Early Cretaceous, Aptian) of northeastern Thailand". Annales de Paléontologie. 97 (1–2): 51–62. doi:10.1016/j.annpal.2011.08.001.CS1 maint: Uses authors parameter (link)
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Aralosaurini

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Brachylophosaurini

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Canardia

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Choyrodon

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Elasmaria

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Hadrosauroidea

Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and all dinosaurs more closely related to them than to Iguanodon.They are from Asia, Europe and Africa. Many primitive hadrosauroids, such as the Asian Probactrosaurus and Altirhinus, have traditionally been included in a paraphyletic (unnatural grouping) "Iguanodontidae". With cladistic analysis, the traditional Iguanodontidae has been largely disbanded, and probably includes only Iguanodon and perhaps its closest relatives.

Iguanodontia

Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include Camptosaurus, Dryosaurus, Iguanodon, Tenontosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodontians were one of the first groups of dinosaurs to be found. They are among the best known of the dinosaurs, and were among the most diverse and widespread herbivorous dinosaur groups of the Cretaceous period.

Jaxartosaurus

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Jeyawati

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Koshisaurus

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Lapampasaurus

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Osmakasaurus

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Penelopognathus

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Plesiohadros

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Rhabdodontomorpha

Rhabdodontomorpha is a clade of basal iguanodont dinosaurs. This group was named in 2016 in the context of the description, based on Spanish findings, of an early member of the Rhabdodontidae. A cladistic analysis was conducted in which it was found that Muttaburrasaurus was the sister species of the Rhabdodontidae sensu Weishampel. Therefore, Paul-Emile Dieudonné, Thierry Tortosa, Fidel Torcida Fernández-Baldor, José Ignacio Canudo and Ignacio Díaz-Martínez defined Rhabdodontomorpha as a nodal clade: the group consisting of the last common ancestor of Rhabdodon priscus Matheron, 1869 and Muttaburrasaurus langdoni Bartholomai and Molnar, 1981; and all its descendants. Within the clade are included also Zalmoxes and Mochlodon.The group consists of small to large plant eaters from Europe and Gondwana. It must have split from other iguanodont groups during the Middle Jurassic.

Sahaliyania

Sahaliyania (from "black" in Manchu, a reference to the Amur/Heilongjiang River) is a genus of lambeosaurine hadrosaurid dinosaur (crested duckbilled dinosaur) from the Late Cretaceous of Heilongjiang, China.

Sirindhorna

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Xuwulong

Xuwulong is a genus of hadrosauroid dinosaur from the Early Cretaceous period. It lived during the early Cretaceous period (Aptian-Albian age) in what is now Yujingzi Basin in the Jiuquan area, Gansu Province of northwestern China. It is known from the holotype – GSGM F00001, an articulated specimen including a complete cranium, almost complete axial skeleton, and complete left pelvic girdle from Xinminpu Group. Xuwulong was named by You Hailu, Li Daqing and Liu Weichang in 2011 and the type species is Xuwulong yueluni.

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