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.
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. In 1998, a tibia and some individual teeth were referred to the species.
Siamotyrannus is a large theropod. Buffetaut estimated its length at seven meters. In 2010, Gregory S. Paul estimated the length at six metres, the weight at half a ton. 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, though due to lacking some of the primary tyrannosauroid synapomorphies that define the clade, its position here is not certain. 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. In 2012 Matthew Carrano e.a. found a position in the Metriacanthosaurinae.
|Illustration of the pelvic bones and tail vertebrae|
Buffetaut et al., 1996
Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1996.Berriasian
In the geological timescale, the Berriasian is an age or stage of the Early Cretaceous. It is the oldest, or lowest, subdivision in the entire Cretaceous. It spanned the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago). The Berriasian succeeds the Tithonian (part of the Jurassic) and precedes the Valanginian.Hauterivian
The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous epoch or a stage in the Lower Cretaceous series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the Valanginian and succeeded by the Barremian.List of Asian dinosaurs
This is a list of dinosaurs whose remains have been recovered from Asia excluding the Indian Subcontinent, which was part of a separate landmass for much of the Mesozoic. This list does not include dinosaurs that live or lived after the Mesozoic era such as birds.List of dinosaur genera
This list of dinosaurs is a comprehensive listing of all genera that have ever been included in the superorder Dinosauria, excluding class Aves (birds, both living and those known only from fossils) and purely vernacular terms.
The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered dinosaurs. Many listed names have been reclassified as everything from birds to crocodilians to petrified wood. The list contains 1559 names, of which approximately 1192 are considered either valid dinosaur genera or nomina dubia.Metriacanthosauridae
Metriacanthosauridae is an extinct family of theropod dinosaurs that lived from the Middle Jurassic to the Early Cretaceous. When broken down into its Greek roots, it means "moderately-spined lizards". The family is split into two subgroups: Metriacanthosaurinae, which includes dinosaurs closely related to Metriacanthosaurus, and another group composed of the close relatives of Yangchuanosaurus. Metriacanthosaurids are considered carnosaurs, belonging to the Allosauroidea superfamily. The group includes species of large range in body size. Of their physical traits, most notable are their neural spines. Their fossils can be found mostly in the Northern hemisphere. Metriacanthosauridae is used as a senior synonym of Sinraptoridae.Metriacanthosaurus
Metriacanthosaurus (meaning "moderately-spined lizard") is a genus of metriacanthosaurid dinosaur from the upper Oxford Clay of England, dating to the Late Jurassic period, about 160 million years ago (lower Oxfordian).Phu Wiang Dinosaur Museum
Phu Wiang Dinosaur Museum (Thai: พิพิธภัณฑ์ไดโนเสาร์ภูเวียง) is a geological museum mainly exhibiting fossils. It is under the administration of the Department of Mineral Resources, Ministry of Natural Resources and Environment, the Royal Thai Government, and situated in the Khok Sanambin public area in Tambon Nai Muang, Wiang Kao district, Khon Kaen province in the northeastern region of Thailand. The museum was constructed with a budget from the Tourism Authority of Thailand under supervision of the Department of Mineral Resources and comprises an area of 40 acres (160,000 m2). It has been open to the public since 2001.Phu Wiang National Park
Phu Wiang National Park (PWNP) is in Phu Wiang District, Khon Kaen Province, northeastern Thailand. It is best known for its numerous dinosaur bone paleontological sites, The park is one of the world's largest dinosaur graveyards. In 1996, the remains of Siamotyrannus isanensis, a new family of carnivorous thunder lizards, were unearthed in the park.
The Phu Wiang Dinosaur Museum in the park displays many of the park's finds. The park, measuring 325 square kilometres (125 sq mi) in size, is approximately 85 kilometres (53 mi) northwest of Khon Kaen. The area is characterized by a central plain and the low hills of the western Phu Phan Mountains.Sao Khua Formation
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.
Dinosaur remains are among the fossils that have been recovered from the formation.Siats
Siats is an extinct genus of large neovenatorid theropod dinosaur known from the Late Cretaceous Cedar Mountain Formation of Utah, US. It contains a single species, Siats meekerorum. S. meekerorum could be the first neovenatorid discovered in North America and the geologically youngest allosauroid yet discovered from the continent. It was initially classified as a megaraptoran, a clade of large theropods with very controversial relationships. This group may be examples of tyrannosauroids, neovenatorid allosauroids, or basal coelurosaurs.Timeline of tyrannosaur research
This timeline of tyrannosaur research is a chronological listing of events in the history of paleontology focused on the tyrannosaurs, a group of predatory theropod dinosaurs that began as small, long-armed bird-like creatures with elaborate cranial ornamentation but achieved apex predator status during the Late Cretaceous as their arms shrank and body size expanded. Although formally trained scientists did not begin to study tyrannosaur fossils until the mid-19th century, these remains may have been discovered by Native Americans and interpreted through a mythological lens. The Montana Crow tradition about thunder birds with two claws on their feet may have been inspired by isolated tyrannosaurid forelimbs found locally. Other legends possibly inspired by tyrannosaur remains include Cheyenne stories about a mythical creature called the Ahke, and Delaware stories about smoking the bones of ancient monsters to have wishes granted.Tyrannosaur remains were among the first dinosaur fossils collected in the United States. The first of these was named Deinodon horridus by Joseph Leidy. However, as this species was based only on teeth the name would fall into disuse. Soon after, Edward Drinker Cope described Laelaps aquilunguis from a partial skeleton in New Jersey. Its discovery heralded the realization that carnivorous dinosaurs were bipeds, unlike the lizardlike megalosaurs sculpted for the Crystal Palace. Laelaps was also among the first dinosaurs to be portrayed artistically as a vigorous, active animal, presaging the Dinosaur Renaissance by decades. Later in the century, Cope's hated rival Othniel Charles Marsh would discover that the name Laelaps had already been given to a parasitic mite, and would rename the dinosaur Dryptosaurus.Early in the 20th century, Tyrannosaurus itself was discovered by Barnum Brown and named by Henry Fairfield Osborn, who would recognize it as a representative of a distinct family of dinosaurs he called the Tyrannosauridae. Tyrannosaur taxonomy would be controversial for many decades afterward. One controversy centered around the use of the name Tyrannosauridae for this family, as the name "Deinodontidae" had already been proposed. The name Tyrannosauridae came out victorious following arguments put forth by Dale Russell in 1970. The other major controversy regarding tyrannosaur taxonomy was the family's evolutionary relationships. Early in the history of paleontology, it was assumed that the large carnivorous dinosaurs were all part of one evolutionary lineage ("carnosaurs"), while the small carnivorous dinosaurs were part of a separate lineage (coelurosaurs). Tyrannosaurid anatomy led some early researchers like Matthew, Brown, and Huene, to cast doubt on the validity of this division. However, the traditional carnosaur-coelurosaur division persisted until the early 1990s, when the application of cladistics to tyrannosaur systematics confirmed the doubts of early workers and found tyrannosaurs to be large-bodied coelurosaurs.Another debate about tyrannosaurs would not be settled until the early 21st century: their diet. Early researchers were so overwhelmed by the massive bulk of Tyrannosaurus that some, like Lawrence Lambe, were skeptical that it was even capable of hunting down live prey and assumed that it lived as a scavenger. This view continued to be advocated into the 1990s by Jack Horner but was shown false by Kenneth Carpenter, who reported the discovery of a partially healed tyrannosaur bite wound on an Edmontosaurus annectens tail vertebra, proving that T. rex at least sometimes pursued living victims.Tyrannosauridae
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three. All of these animals lived near the end of the Cretaceous Period and their fossils have been found only in North America and Asia.
Although descended from smaller ancestors, tyrannosaurids were almost always the largest predators in their respective ecosystems, putting them at the apex of the food chain. The largest species was Tyrannosaurus rex, one of the largest and most massive known land predators, which measured over 12.3 metres (40 ft) in length and according to most modern estimates 8.4 metric tons (9.3 short tons) to 14 metric tons (15.4 short tons) in weight. Tyrannosaurids were bipedal carnivores with massive skulls filled with large teeth. Despite their large size, their legs were long and proportioned for fast movement. In contrast, their arms were very small, bearing only two functional digits.
Unlike most other groups of dinosaurs, very complete remains have been discovered for most known tyrannosaurids. This has allowed a variety of research into their biology. Scientific studies have focused on their ontogeny, biomechanics and ecology, among other subjects.Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) 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, Asia, South America and Australia.
Tyrannosauroids were bipedal carnivores, as were most theropods, and were characterized by numerous skeletal features, especially of the skull and pelvis. Early in their existence, tyrannosauroids were small predators with long, three-fingered forelimbs. Late Cretaceous genera became much larger, including some of the largest land-based predators ever to exist, but most of these later genera had proportionately small forelimbs with only two digits. Primitive feathers have been identified in fossils of two species, and may have been present in other tyrannosauroids as well. Prominent bony crests in a variety of shapes and sizes on the skulls of many tyrannosauroids may have served display functions.Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian stage succeeds the Berriasian stage of the Lower Cretaceous and precedes the Hauterivian stage of the Lower Cretaceous.Varavudh Suteethorn
Varavudh Suteethorn, or Warawut Suteethorn (Thai:วราวุธ สุธีธร; born October 10, 1948) 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.Yangchuanosaurus
Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China during the Bathonian and Callovian stages of the Middle Jurassic, and was similar in size and appearance to its North American and European relative, Allosaurus. It hails from the Upper Shaximiao Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. It was named after the area in which was discovered, Yongchuan, in China.Éric Buffetaut
Éric Buffetaut (born 19 November 1950) is a French paleontologist, author and researcher at the Centre national de la recherche scientifique since 1976 where he is a Doctor of Science and Director of Research. Buffetaut is a specialist of fossil archosaurs, mainly dinosaurs and pterosaurs, and has published a large number of books on paleontology. He is one of the major paleontologists to support the thesis of the fall of a meteorite as the main cause of the Cretaceous–Paleogene extinction event.