Raptorex
Encyclopedia
Raptorex is a dubious
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
, "robber", and , "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.
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 Iren Dabasu
or similar formation. Because the specimen is a juvenile, and the changes undergone by tyrannosaurids during growth are not yet well understood, many researchers now consider it to be a nomen dubium, because 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).
, which retained features characteristic of more basal other coelurosaurs
such as a small head and long, three-fingered forelimbs.
The specimen is a very small juvenile, estimated at 3 m (9.8 ft) long and about 65 kg (143.3 lb). The holotype
(LH PV18) measured about 2.5 m (8.2 ft) and died in its third year.
of the specimen. Sereno believed that the specimen was misidentified—rather than a juvenile Tarbosaurus from Mongolia, he identified it as 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.
s present in the rock slab surrounding the specimen showed it was Early Cretaceous in age. 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." However, only a single fish vertebra and a crushed, unidentifiable mollusk shell were actually present alongside the Raptorex specimen. Sereno and colleagues identified the fish vertebra as being similar to the genus Lycoptera
, a key index fossil of the early Cretaceous Yixian formation. However, they did not describe the bone or note any features in common with known Lycoptera specimens.
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.
, 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 ontogeny and stratigraphic position. 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 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 a 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.
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of tyrannosaurid
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. Its fossil remains consist of a single juvenile specimen probably uncovered in Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, or possibly northeastern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is R. kriegsteini, described in 2009 by Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
and colleagues. The genus name is derived from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "robber", and , "king". The specific name honours Roman Kriegstein, a survivor of the Holocaust, whose son Henry Kriegstein donated the specimen to the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
for scientific study.
While initially considered to have come from the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
of China, dated to approximately 125 million years ago during the early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
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 Iren Dabasu
Iren Dabasu Formation
The Iren Dabasu Formation is a Mesozoic geologic formation. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.-Ornithischians:-Saurischians:-References:...
or similar formation. Because the specimen is a juvenile, and the changes undergone by tyrannosaurids during growth are not yet well understood, many researchers now consider it to be a nomen dubium, because 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).
Description
The only known Raptorex specimen shows the same basic proportions as juvenile tyrannosauroids: 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 DilongDilong (dinosaur)
Dilong is a genus of small tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 130 million years ago...
, which retained features characteristic of more basal other coelurosaurs
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
such as a small head and long, three-fingered forelimbs.
The specimen is a very small juvenile, estimated at 3 m (9.8 ft) long and about 65 kg (143.3 lb). The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
(LH PV18) measured about 2.5 m (8.2 ft) and died in its third year.
Discovery
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 SerenoPaul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
of the specimen. Sereno believed that the specimen was misidentified—rather than a juvenile Tarbosaurus from Mongolia, he identified it as 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.
Initial interpretation
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 fossilIndex fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
s present in the rock slab surrounding the specimen showed it was Early Cretaceous in age. 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." However, only a single fish vertebra and a crushed, unidentifiable mollusk shell were actually present alongside the Raptorex specimen. Sereno and colleagues identified the fish vertebra as being similar to the genus Lycoptera
Lycoptera
Lycoptera is a genus of fish that lived from the late Jurassic to Cretaceous periods in present-day China, Korea, Mongolia and Siberia. It is known from abundant fossils representing sixteen species, and is an important index fossil used to date geologic formations in China...
, a key index fossil of the early Cretaceous Yixian formation. However, they did not describe the bone or note any features in common with known Lycoptera specimens.
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.
Controversy and re-interpretation
In October 2010 an online Nature News report (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.Black Hills Institute of Geological Research, Inc.
The Black Hills Institute of Geological Research, Inc. is a private corporation specializing in the excavation and preparation of fossils, as well as the sale of both original fossil material and museum-quality replicas...
, a private fossil excavation and supply company, inspected the fossil and told Nature that he concluded it was a juvenile Tarbosaurus
Tarbosaurus
Tarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
. 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
PLoS ONE
PLoS ONE is an open access peer-reviewed scientific journal published by the Public Library of Science since 2006. It covers primary research from any discipline within science and medicine. All submissions go through an internal and external pre-publication peer review but are not excluded on the...
by Denver Fowler, Peter Larson and others reanalyzing the published data, which they stated to be equivocal regarding ontogeny and stratigraphic position. 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 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 a 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.