Raptorex Temporal range: Late Cretaceous, | |
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Holotype skeleton, Tokyo | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Family: | † Tyrannosauridae |
Genus: | † Raptorex Sereno et al., 2009 |
Species: | †R. kriegsteini |
Binomial name | |
†Raptorex kriegsteini Sereno et al., 2009 | |
Synonyms | |
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Raptorex is a genus of tyrannosaurid dinosaur. Its fossil remains consist of a single juvenile specimen probably uncovered in Mongolia, or possibly northeastern China. The type species is R. kriegsteini, described in 2009 by Sereno and colleagues. The genus name is derived from Latin raptor, "robber", and rex, "king". The specific name honours Roman Kriegstein, a survivor of the Holocaust, whose son Henry Kriegstein donated the specimen to the University of Chicago for scientific study. [1] [2]
While initially considered to have come from the Yixian Formation of China, dated to approximately 125 million years ago during the early Cretaceous period, later studies showed that such an early date for the fossil are unlikely, and given its extremely close similarity to juvenile tyrannosaurids of the late Cretaceous, it probably came from the Nemegt or similar formation. The specimen is a juvenile and many researchers now consider it to be a nomen dubium, because the changes undergone by tyrannosaurids during growth are not yet well understood, so it cannot be confidently paired with an adult skeleton (though it is extremely similar to juvenile Tarbosaurus bataar skeletons of the same size and age), [3] but recently an argument has been made supporting its validity. [4]
According to Peter Larson, who attempted to re-trace the origins of the specimen, the holotype fossil of Raptorex (currently designated LH PV18 and housed in the collections of the Long Hao Institute of Geology and Paleontology in Hohhot, Inner Mongolia, China) was purchased from a Mongolian fossil dealer by an American businessman in Tokyo, Japan, and subsequently taken to the United States, where it was again put up for sale at the Tucson, Arizona Gem, Mineral and Fossil Show. There it was sold by Hollis Butts to Dr. Henry Kriegstein, an ophthalmologist and fossil collector. Up until this point, the specimen had been identified as a juvenile specimen of Tarbosaurus , which had been collected from Mongolia. Kriegstein notified American paleontologist Paul Sereno of the specimen, who proposed it represented a subadult of a new species from the Yixian Formation of China. Sereno arranged to publish a description of the specimen and to have it sent to China, from where he assumed it had been smuggled. [3]
In Sereno's description of the specimen, he and his co-authors interpreted it as a near-adult aged about six years. Sereno initially stated to the press that numerous index fossils present in the rock slab surrounding the specimen showed it belonged to Early Cretaceous. In an interview with the Chicago Tribune, Sereno said “From sediments, fossil fish bones, turtles, clam shells and other fauna we recovered from the rock matrix alongside the Raptorex fossil, we could generally pinpoint where it had been dug up in an area along the border with Inner Mongolia." [5] However, only a single fish vertebra and a crushed, unidentifiable mollusk shell were actually present alongside the Raptorex specimen. [1] [3] Sereno and colleagues identified the fish vertebra as being similar to the genus Lycoptera , a key index fossil of the early Cretaceous Yixian formation. [1] However, they did not describe the bone or note any features in common with known Lycoptera specimens. [3]
Sereno's interpretation of the specimen as an early, primitive, non-tyrannosaurid tyrannosauroid would have major implications for the evolution of tyrannosaurs. Rather than evolving their distinct anatomy of a large head, long legs and tiny, two-fingered arms only after large body size, a small, early Cretaceous species with similar proportions to adults of true tyrannosaurids would indicate that the characteristic tyrannosaur shape appeared prior to the advent of giant size in the group. This would contradict previous evidence, as all previously known primitive tyrannosaurs had small skulls and long, three-fingered arms, including contemporary species and those that lived later in the Cretaceous than Sereno believed Raptorex to have lived. [1]
In October 2010 an online Nature News report [6] (not peer-reviewed) challenged the provenance and classification of Raptorex as a basal tyrannosauroid. Peter Larson, president of the Black Hills Institute of Geological Research, Inc., a private fossil excavation and supply company, inspected the fossil and told Nature that he concluded it was a juvenile Tarbosaurus . Because the specimen was donated by a collector without detailed provenance information, Larson doubted the assigned age, which was based only on the Lycoptera vertebra and mollusk shell found alongside the dinosaur fossil. Larson speculated that the fossil could have come from beds in Mongolia that yield fossils of Tarbosaurus, dating from 70 million years ago. He has suggested "a more detailed analysis of the fossil matrix—including dating of any pollen associated with the fossil." Sereno is quoted in the report as standing by his conclusions, noting that definite evidence or a publication had not been produced refuting them.
In June 2011, a more detailed re-study was published in the peer-reviewed journal PLoS ONE by Denver Fowler, Peter Larson and others reanalyzing the published data, which they stated to be equivocal regarding stratigraphic position, and that ontogenetic interpretation in the description had overestimated the maturity of the specimen. While Sereno had claimed that the vertebrae of Raptorex were nearly fused, and that the bone histology of the specimen indicated it was a subadult about six years old, Fowler and colleagues argued that Sereno and his team had misinterpreted the growth stage data, and found that the specimen was actually a young juvenile only about three years old. They also found fault with the Sereno team's interpretation of the specimen's age. Fowler and colleagues showed that the fish bone which Sereno had identified as Lycoptera without comment is actually very different in shape and much larger in size than any known specimen of Lycoptera and cannot even be assigned to the same order as that genus. Rather, it probably belonged to an ellimmichthyiform fish, which span the entire Cretaceous period, rendering the bone useless for dating. In light of this, they noted that there is no reason to believe the fossil dates to the early Cretaceous, and that given its extreme similarity to juvenile tyrannosaurids, a late Cretaceous age is far more likely. Based on this analysis, Fowler and colleagues concluded that Raptorex was much more likely to represent a juvenile tyrannosaurid similar to Tarbosaurus, though its exact identity cannot be known without more information about growth patterns in tyrannosaurids, and further efforts to discover its age. Consequently, Sereno's hypothesis that the derived features of tyrannosaurids evolved in the Early Cretaceous cannot be supported by current evidence. [3]
Newbrey et al. (2013) identified the fish vertebra centrum found with the holotype specimen of Raptorex kriegsteini as belonging to a hiodontid, probably representing the same taxon as hiodontid fossils described by the authors from the Late Cretaceous Nemegt Formation of Mongolia. According to Newbrey et al., centra like those of the Nemegt hiodontid are not known from outside the Nemegt Formation; according to the authors, this implies that the vertebra found with the holotype specimen of Raptorex kriegsteini – and by extension the holotype of R. kriegsteini itself – most likely come from the Nemegt Formation and are Late Cretaceous in age. [7] Kim et al. (2022) compared a fish centrum found with the holotype of Raptorex with Harenaichthys lui from the Nemegt Formation and Chinese Xixiaichthys tongxinensis, and interpreted their findings as supporting the conclusion that the holotype of R. kriegsteini comes from the Nemegt Formation. [8]
In 2022, the results of a restudy of the Raptorex specimen were included in an article focusing on the tyrannosauroids of the Iren Dabasu Formation by researcher Thomas Carr. He agreed with Fowler et al. that the specimen represented a juvenile, but contrarily to Fowler et al., Carr found it to be a valid taxon based on several features of the skull not found in any tyrannosaurid. Additionally, he did not find a subcutaneous flange of the maxilla in Raptorex, which is a unique feature of juvenile Tarbosaurus. [4]
The only known Raptorex specimen shows the same basic proportions as juvenile tyrannosaurids: a comparatively large and solidly-constructed skull, long legs with adaptations for running, and tiny, two-fingered forelimbs. This is in contrast with more basal tyrannosauroids such as Dilong , which retained features characteristic of more basal coelurosaurs such as a small head and long, three-fingered forelimbs. [1]
The specimen is a very small juvenile, estimated at 3 m (9.8 ft) long and about 65 kg (143 lb). The holotype (LH PV18) measured about 2.5 m (8.2 ft) and died in its third year. [3]
Raptorex has been interpreted as a tyrannosaurid, tyrannosauroid and a synonym of Tarbosaurus. It is currently placed as a basal tyrannosauroid more derived than Bagaraatan but more basal than Dryptosaurus . [9]
Below is a cladogram placing Raptorex as a basal tyrannosauroid. It was published by Loewen et al. in 2013 on PLoS ONE. [9]
Carr (2022) considered Raptorex to be closely related to derived tyrannosaurines, because it and a juvenile tyrannosaurid from the Iren Dabasu Formation shared unique characteristics with juvenile Tyrannosaurus and adult Tarbosaurus. [4]
Tyrannosauridae 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.
Tarbosaurus is a genus of tyrannosaurine theropod dinosaur that lived in Asia about 70 million years ago, during the Maastrichtian age at the end of the Late Cretaceous period, considered to contain a single known species: Tarbosaurus bataar. Fossils have been recovered from the Nemegt and Djadochta Formations of Mongolia, with more fragmentary remains found further afield in China.
Daspletosaurus is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 78 and 74.4 million years ago, during the Late Cretaceous Period. The genus Daspletosaurus contains three named species. Fossils of the earlier type species, D. torosus, have been found in Alberta, while fossils of a later species, D. horneri, have been found only in Montana. D. wilsoni has been suggested as an intermediate species between D. torosus and D. horneri that evolved through anagenesis, but this theory has been disputed by other researchers.
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Canadian province of Alberta and the U.S. state of Montana. Paleontologists recognize only the type species, G. libratus, although other species have been erroneously referred to the genus.
Alectrosaurus is a genus of tyrannosauroid theropod dinosaur that lived in Asia during the Late Cretaceous period, about some 96 million years ago in what is now the Iren Dabasu Formation.
Alioramus is a genus of tyrannosaurid theropod dinosaurs from the Late Cretaceous period of Asia. It currently contains two species. The type species, A. remotus is known from a partial skull and three foot bones recovered from the Mongolian Nemegt Formation, which was deposited in a humid floodplain about 70 million years ago. These remains were named and described by Soviet paleontologist Sergei Kurzanov in 1976. A second species, A. altai, known from a much more complete skeleton also from the Nemegt Formation, was named and described by Stephen L. Brusatte and colleagues in 2009. Its relationships to other tyrannosaurid genera were at first unclear, with some evidence supporting a hypothesis that Alioramus was closely related to the contemporary species Tarbosaurus bataar. However, the discovery of Qianzhousaurus indicates that it belongs to a distinct branch of tyrannosaurs, namely the tribe Alioramini.
Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4–13 m (37–43 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.
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.
Bagaraatan is a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongolia. Bagaraatan may have been around 3 to 4 metres in length.
Tyrannosaurinae is one of the two extinct subfamilies of Tyrannosauridae, a family of coelurosaurian theropods that consists of at least three tribes and several genera. All fossils of these genera have been found in the Late Cretaceous deposits of western North America and east Asia. Compared to the related subfamily Albertosaurinae, tyrannosaurines overall are more robust and larger though the alioramins were gracile by comparison. This subfamily also includes the oldest known tyrannosaurid genus Lythronax as well as the youngest and most famous member of the group, Tyrannosaurus rex. There were at least 30 different species of tyrannosaurines.
Coriops is an extinct genus of freshwater osteoglossomorph fish, with a single species known from the Late Cretaceous and Paleocene of western North America.
Bistahieversor, also known as the "Bisti Beast", is a genus of basal eutyrannosaurian theropod dinosaur. The genus contains only a single known species, B. sealeyi, described in 2010, from the Late Cretaceous of New Mexico. The holotype and a juvenile were found in the Hunter Wash Member of the Kirtland Formation, while other specimens came from the underlying Fossil Forest member of the Fruitland Formation. This dates Bistahieversor approximately 75.5 to 74.5 million years ago during the Campanian age, found in sediments spanning a million years.
Yutyrannus is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, Yutyrannus huali. This species lived during the early Cretaceous period in what is now northeastern China. Three fossils of Yutyrannus huali —all found in the rock beds of Liaoning Province— are currently the largest-known dinosaur specimens that preserve direct evidence of feathers.
Lythronax is a genus of tyrannosaurid dinosaur that lived in North America around 81.9-81.5 million years ago during the Late Cretaceous period. The only known specimen was discovered in Utah in the Wahweap Formation of the Grand Staircase–Escalante National Monument in 2009, and it consists of a partial skull and skeleton. In 2013, it became the basis of the new genus and species Lythronax argestes; the generic name Lythronax means "gore king", and the specific name argestes originates from the Greek poet Homer's name for the wind from the southwest, in reference to the specimen's geographic provenance in North America.
Suskityrannus is a genus of small tyrannosauroid theropod from the Late Cretaceous in southern Laramidia. It contains a single species, Suskityrannus hazelae, and the type specimen was found in the Turonian-age Moreno Hill Formation of the Zuni Basin in western New Mexico.
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.
Timurlengia is an extinct genus of tyrannosauroid theropod dinosaur found in Uzbekistan, in the Bissekty Formation in the Kyzylkum Desert, hailing from the Turonian age of the early Late Cretaceous. The type species is Timurlengia euotica.
Oksoko is a genus of oviraptorid dinosaur from the Late Cretaceous of Asia, that lived in what is now the Nemegt Formation in Mongolia. It includes the type species Oksoko avarsan.
Harenaichthys is an extinct genus of osteoglossiform fish that lived in Mongolia during the Late Cretaceous and was found in the Nemegt Formation. The type species is H. lui and is based solely on the holotype, which consists of partial skull parts, isolated and articulated centra, and an articulated caudal fin preserved together within a single sandstone block. The monospecific assemblages of Harenaichthys were affected by the high altitude of their habitat and the fossils show signs of pathologies caused by diseases while the animals were still alive.
Xixiaichthys is an extinct genus of osteoglossiform fish that lived in China during the Early Cretaceous and was found in the Madongshan Formation and also the Xinminbao Group. The type species is Xixiaichthys tongxiensis and is based on the holotype, a complete skeleton, and several other specimens of varying completeness.
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