| Siamotyrannus Temporal range: Early Cretaceous, | |
|---|---|
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| Illustration of the pelvic bones and tail vertebrae | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avetheropoda |
| Genus: | † Siamotyrannus Buffetaut, Suteethorn & Tong, 1996 |
| Species: | †S. isanensis |
| Binomial name | |
| †Siamotyrannus isanensis | |
Siamotyrannus (meaning "Siamese tyrant") is a genus of theropod dinosaur from the early Cretaceous of Thailand.
In 1993, Somchai Traimwichanon found a partial skeleton of a large theropod at the Phu Wiang 9 site in Khon Kaen.
In 1996, Eric Buffetaut, Varavudh Suteethorn and Haiyan Tong named and described the type species Siamotyrannus isanensis. The generic name is derived from the old Thai kingdom of Siam, and a Latinised Greek tyrannus, meaning "tyrant", in reference to a presumed membership of the Tyrannosauridae. The specific name is derived from Thai isan, "northeastern part", referring to the provenance from northeast Thailand. [1]
The holotype, PW9-1, was found in the Sao Khua Formation, dating from the Berriasian-Barremian. It includes the left half of the pelvis, five rear dorsal vertebrae, the sacrum with five sacrals, and thirteen front tail vertebrae. [1] In 1998, a tibia and some individual teeth were referred to the species. [2]
Siamotyrannus is a large theropod. Buffetaut estimated its length at seven meters. In 2010, Gregory S. Paul estimated the length at 6 meters (20 ft), the weight at 500 kg. [3] In 2016 Molina-Pérez and Larramendi gave a higher estimation of 10 meters (33 ft) and 1.75 tonnes (1.93 short tons). [4] A possible autapomorphy, unique derived trait, is the possession of two vertical ridges on the ilium. The second and third sacrals are strongly transversely flattened.
As evidenced by its name, it was originally thought to be a tyrannosauroid and even a tyrannosaurid, [1] though due to lacking some of the primary tyrannosauroid synapomorphies that define the clade, its position here is not certain. [5] Some analyses have categorized Siamotyrannus as a primitive carnosaur rather than a basal tyrannosauroid, and it has several features that may determine it to be an allosaurid or a sinraptorid. [6] In 2012 Matthew Carrano et al. found a position in the Metriacanthosaurinae. [7] Later studies consider its position uncertain within Avetheropoda, finding it to be either an allosauroid or a primitive coelurosaur. [8] In his 2024 review of theropod relationships, Cau recovered it as a tetanuran outside of the Orionides, as a close relative of Siamraptor . [9]
Tetanurae is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans. Tetanurans are defined as all theropods more closely related to modern birds than to Ceratosaurus and contain the majority of predatory dinosaur diversity. Tetanurae likely diverged from its sister group, Ceratosauria, during the late Triassic. Tetanurae first appeared in the fossil record by the Early Jurassic about 190 mya and by the Middle Jurassic had become globally distributed.
Allosauridae is a family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in 1878. Allosaurids are characterized by an astragalus with a restriction of the ascending process to the lateral part of the bone, a larger medial than lateral condyle, and a horizontal groove across the face of the condyles.
Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).
Tyrannosauroidea is a superfamily of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent beginning in the Jurassic Period. By the end of the Cretaceous Period, tyrannosauroids were the dominant large predators in the Northern Hemisphere, culminating in the gigantic Tyrannosaurus. Fossils of tyrannosauroids have been recovered on what are now the continents of North America, Europe and Asia, with fragmentary remains possibly attributable to tyrannosaurs also known from South America and Australia.
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 an extinct genus of ornithomimosaurian theropod dinosaur that was discovered in the Early Cretaceous Sao Khua Formation in what is now Thailand. The genus contains only the type species, K. khonkaenensis. The specific epithet is after Khon Kaen Province, which is in northeastern Thailand, where the remains of the animal were dicovered.
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.
Lophostropheus is an extinct genus of coelophysoid theropod dinosaur that lived approximately 205.6 to 196.5 million years ago during the boundary between the Late Triassic Period and the Early Jurassic Period, in what is now Normandy, France. Lophostropheus is one of the few dinosaurs that may have survived the Triassic–Jurassic extinction event.
Aerosteon is a genus of megaraptoran dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the Anacleto Formation, which is from the late Campanian. The type and only known species is A. riocoloradensis. Its specific name indicates that its remains were found 1 km north of the Río Colorado, in Mendoza Province, Argentina.
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.
Shidaisaurus is a genus of metriacanthosaurid dinosaur. Its fossil was found in early Middle Jurassic-age rocks of the Chuanjie Formation in Yunnan, China. It is known from a partial skeleton, holotype DML-LCA 9701-IV, found at the bottom of an assemblage of nine dinosaur individuals, lacking most of the tail vertebrae, ribs, pectoral girdle, and limb bones. Shidaisaurus was described in 2009 by Wu and colleagues. The type species is Shidaisaurus jinae. Generic name and specific name in combination refer to the Jin-Shidai Company that oversaw excavation and inspection of the Jurassic World Park near the site.
Megaraptora is a clade of carnivorous theropod dinosaurs with controversial relationships to other tetanuran theropods. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods.
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.
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.
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.
Yunmenglong is an extinct genus of somphospondylan sauropod known from the late Early Cretaceous of Henan Province, central China. Its remains were discovered in the Haoling Formation of the Ruyang Basin. The type species is Yunmenglong ruyangensis, described in 2013 by Junchang Lü et al. on the basis of an incomplete postcranial skeleton. Yunmenglong shares some characters with Euhelopus, Qiaowanlong and Erketu, and a phylogenetic analysis places it as a sister taxon of Qiaowanlong, both grouped with Erketu in a position more derived than Euhelopus but basal to Titanosauria.
Siats (/see-ats/) is an extinct genus of large theropod dinosaur known from the Late Cretaceous Cedar Mountain Formation of Utah, United States. It contains a single species, Siats meekerorum. It was initially classified as a megaraptoran, a clade of large theropods with very controversial relationships. Siats may be a neovenatorid allosauroid, a coelurosaur of uncertain phylogenetic position, or a tyrannosauroid.
Datanglong is an extinct genus of theropod belonging to either Carcharodontosauria or Megaraptora. It existed during the Early Cretaceous (Barremian-Albian) in what is now southeastern China.
Varavudh Suteethorn, or Warawut Suteethorn is a Thai palaeontologist and geologist. He is the current director of the Palaeontological Research and Education Centre, Mahasarakham University. He is best known for his work on vertebrate paleontology 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.
Phuwiangvenator is an extinct genus of megaraptoran theropod that lived during the Early Cretaceous period in what is now Thailand. It contains only the type species, P. yaemniyomi. The generic name of Phuwiangvenator comes from the Phu Wiang mountains, where the holotype was discovered, and the Latin word "venator" meaning hunter. The specific name, "yaemniyomi", is in honor of Sudham Yaemniyom, who was a historical paleontologist from Thailand and the first person to discover fossils there.
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