Tianyuraptor
Encyclopedia
Tianyuraptor is a genus
of short-armed dromaeosaurid
dinosaur
('running lizard'; a type of small dinosaur considered to be closely related to birds) that lived during the Early Cretaceous
, about 122 million years ago. Its remains have been found in western Liaoning
, China
. It was similar to other dromaeosaurids found in Liaoning, with the exception of being somewhat more primitive
. The type specimen, formally named in 2010
, shows features not seen in previously known Northern Hemisphere (Laurasia
n) dromaeosaurids, but present in Southern Hemisphere (Gondwana
n) species and early birds
. Because of this, the scientists who first studied Tianyuraptor described it as a "transitional species
", bridging the gap between northern and southern types of dromaeosaurid. Tianyuraptor also differs from previously known dromaeosaurids in that it possesses a relatively small furcula
("wishbone"), and unusually short forelimbs.
name of Tianyuraptor combines Tianyu, referring to the Shandong Tianyu Museum of Nature where the holotype
specimen is stored, with raptor, the Latin word for 'robber', referring to the action of grabbing prey, often used in naming dromaeosaurids. The specific epithet, ostromi, is in honor of John Ostrom
, who contributed greatly to the study of dromaeosaurid fossils, including Deinonychus
and feathered dinosaurs
.
features that separate it from other dromaeosaurids. These include the length of the middle caudal (tail) vertebrae being more than twice that of the dorsal (back) vertebrae, a small and extremely slender furcula
, and an unusually long hindlimb that is roughly three times as long as the entire series of dorsal vertebrae. As in other dromaeosaurid fossils discovered in Liaoning, the tail is relatively long at 960 millimetres (37.8 in), nearly 4.8 times as long as the femur.
The type specimen
is STM1–3, a nearly complete and fully articulated skeleton that is only missing the extreme distal end of the tail. A total of 25 fully articulated caudal vertebrae are preserved and at the end three at most are estimated to be missing. The fossil
was discovered in the Dawangzhangzi Bed of the Yixian Formation
(Jehol Group), located in Lingyuan in western Liaoning
, China. The Yixian Formation is an Early Cretaceous
rock unit, dated to between approximately 129.7 and 122.1 million years old, in the Barremian
and Aptian
faunal stages. The Dawangzhangzi Bed specifically has been dated to about 122 million years ago. STM1–3 is believed to be a sub-adult, with features including the incomplete fusion of skeletal parts during ontogeny
. The holotype of Tianyuraptor preserves no soft tissues, unlike many other theropod specimens from the Jehol Group.
While Tianyuraptor is larger in size than all other known microraptorines
, it also has relatively elongated lower hindlimbs, like other microraptorines. In this regard, it is different from most other dromaeosaurids, which have relatively short lower legs. For example, Tianyuraptor has a tibiotarsus
/femur length ratio of greater than 1.30, while Velociraptor mongoliensis, a creature of similar size, exhibits a ratio of less than 1.10. Aside from elongate hind limbs, Tianyuraptor is different from other members of Microraptorinae in regards to the relative lengths of the forelimb elements. The forelimbs of Tianyuraptor are proportionally much shorter than those of larger dromaeosaurids. For example, a similar-sized Velociraptor
specimen shows an arm/leg length ratio of approximately 0.75., while Tianyuraptor has an arm/leg ratio of 0.53.
, have been suggested to have been aerodynamic and may have glided. Microraptorines are usually noted for their long and robust forelimbs and large, asymmetrical flight feather
s. However, the shortened forelimbs, small furcula, and the transversely wide coracoid in Tianyuraptor suggest that it was not suited for aerodynamic gliding or flight.
analysis performed by Zheng et al. showed Tianyuraptor to be a basal
member of a group containing Laurasia
n dromaeosaurids. Tianyuraptor seems to possess several features that are unknown in other Laurasian dromaeosaurids, but which are seen in basal avialans
and Gondwana
n dromaeosaurids, including Austroraptor
, Buitreraptor
, Neuquenraptor
, Rahonavis
, and Unenlagia
. Zheng and colleagues also noted that Tianyuraptor shares some features with the monophyletic
subfamily
Microraptorinae
, though they went on to say that this mixture of features suggests a basal placement for Tianyuraptor within Microraptorinae, as evidenced by their phylogenetic analysis which indicated maximum parsimony
in six of the 30 results recovered by the analysis. The authors then go on to suggest that since Tianyuraptor is considered a short-armed microraptorine, more derived
long-armed microraptorines might have independently evolved flight capability. However, it is also equally possible, as argued by Zheng et al., that Tianyuraptor may in fact be a basal member of a clade
containing all other Laurasia
n dromaeosaurids with the exception of Microraptorinae. This is indicated by the other 24 out of 30 most parsimonious trees recovered from the analysis. The discovery of Tianyuraptor sheds new light on the early evolution of dromaeosaurs and further exemplifies the great diversity this group enjoyed at an early stage.
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 short-armed dromaeosaurid
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
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...
('running lizard'; a type of small dinosaur considered to be closely related to birds) that lived during the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
, about 122 million years ago. Its remains have been found in western Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, 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...
. It was similar to other dromaeosaurids found in Liaoning, with the exception of being somewhat more primitive
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
. The type specimen, formally named in 2010
2010 in paleontology
-Anomalocaridids:-Newly named crustaceans:-Newly named insects:* A new family, Cascopleciidae, is published by Poinar Jr.* A new family of ceraphronoid Hymenopters, Radiophronidae, is published by Ortega-Blanco, Rasnitsyn, and Delclòs....
, shows features not seen in previously known Northern Hemisphere (Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n) dromaeosaurids, but present in Southern Hemisphere (Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n) species and early birds
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
. Because of this, the scientists who first studied Tianyuraptor described it as a "transitional species
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...
", bridging the gap between northern and southern types of dromaeosaurid. Tianyuraptor also differs from previously known dromaeosaurids in that it possesses a relatively small furcula
Furcula
The ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
("wishbone"), and unusually short forelimbs.
Etymology
The genericGenus
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...
name of Tianyuraptor combines Tianyu, referring to the Shandong Tianyu Museum of Nature where 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...
specimen is stored, with raptor, the Latin word for 'robber', referring to the action of grabbing prey, often used in naming dromaeosaurids. The specific epithet, ostromi, is in honor of John Ostrom
John Ostrom
John H. Ostrom was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s, when he demonstrated that dinosaurs are more like big non-flying birds than they are like lizards , an idea first proposed by Thomas Henry Huxley in the 1860s, but which had garnered...
, who contributed greatly to the study of dromaeosaurid fossils, including Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
and feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
.
Description
Tianyuraptor is a medium-sized dromaeosaurid that has several derivedDerived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
features that separate it from other dromaeosaurids. These include the length of the middle caudal (tail) vertebrae being more than twice that of the dorsal (back) vertebrae, a small and extremely slender furcula
Furcula
The ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
, and an unusually long hindlimb that is roughly three times as long as the entire series of dorsal vertebrae. As in other dromaeosaurid fossils discovered in Liaoning, the tail is relatively long at 960 millimetres (37.8 in), nearly 4.8 times as long as the femur.
The type specimen
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...
is STM1–3, a nearly complete and fully articulated skeleton that is only missing the extreme distal end of the tail. A total of 25 fully articulated caudal vertebrae are preserved and at the end three at most are estimated to be missing. The fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
was discovered in the Dawangzhangzi Bed of 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...
(Jehol Group), located in Lingyuan in western Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China. The Yixian Formation is an Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
rock unit, dated to between approximately 129.7 and 122.1 million years old, in the Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
and Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
faunal stages. The Dawangzhangzi Bed specifically has been dated to about 122 million years ago. STM1–3 is believed to be a sub-adult, with features including the incomplete fusion of skeletal parts during ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
. The holotype of Tianyuraptor preserves no soft tissues, unlike many other theropod specimens from the Jehol Group.
Limbs
The forelimbs are comparatively short, being only 53% of the hindlimbs' length. This differs greatly from the known skeletal elements of other dromaeosaurids, most of which have relatively long forelimbs that are more than 70% of the hindlimbs' length.While Tianyuraptor is larger in size than all other known microraptorines
Microraptorinae
Microraptorinae is a subfamily of Dromaeosauridae. Microraptorines were among the most primitive dromaeosaurids. They appeared 125 million years ago in China. Many may have been semi-arboreal gliders...
, it also has relatively elongated lower hindlimbs, like other microraptorines. In this regard, it is different from most other dromaeosaurids, which have relatively short lower legs. For example, Tianyuraptor has a tibiotarsus
Tibiotarsus
The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia.A similar structure also occurred in the Mesozoic Heterodontosauridae...
/femur length ratio of greater than 1.30, while Velociraptor mongoliensis, a creature of similar size, exhibits a ratio of less than 1.10. Aside from elongate hind limbs, Tianyuraptor is different from other members of Microraptorinae in regards to the relative lengths of the forelimb elements. The forelimbs of Tianyuraptor are proportionally much shorter than those of larger dromaeosaurids. For example, a similar-sized Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
specimen shows an arm/leg length ratio of approximately 0.75., while Tianyuraptor has an arm/leg ratio of 0.53.
Paleobiology
The stark difference in arm length compared to other dromaeosaurids implies that the function of the arms in Tianyuraptor was different from that of other dromaeosaurs. Members of the subfamily Microraptorinae, such as MicroraptorMicroraptor
Microraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China...
, have been suggested to have been aerodynamic and may have glided. Microraptorines are usually noted for their long and robust forelimbs and large, asymmetrical flight feather
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
s. However, the shortened forelimbs, small furcula, and the transversely wide coracoid in Tianyuraptor suggest that it was not suited for aerodynamic gliding or flight.
Classification
A phylogeneticPhylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
analysis performed by Zheng et al. showed Tianyuraptor to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of a group containing Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n dromaeosaurids. Tianyuraptor seems to possess several features that are unknown in other Laurasian dromaeosaurids, but which are seen in basal avialans
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
and Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n dromaeosaurids, including Austroraptor
Austroraptor
Austroraptor was a genus of dromaeosaurid dinosaur that lived about 70 million years ago during the Cretaceous period in what is now modern Argentina. The type species for the genus, Austroraptor cabazai, was described in late 2008 by Fernando Novas of the Museo Argentino de Ciencias Naturales...
, Buitreraptor
Buitreraptor
Buitreraptor is a predatory dromaeosaurid theropod dinosaur from the Cretaceous of Argentina.Buitreraptor was described in 2005. The type species is Buitreraptor gonzalezorum...
, Neuquenraptor
Neuquenraptor
Neuquenraptor is a dromaeosaurid theropod dinosaur of the Late Cretaceous of Argentina, one of the first dromaeosaurids found in the Southern Hemisphere....
, Rahonavis
Rahonavis
Rahonavis is a genus of bird-like dinosaur from the Late Cretaceous of what is now northwestern Madagascar. It is known from a partial skeleton found in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province...
, and Unenlagia
Unenlagia
Unenlagia is a genus of, possibly dromaeosaurid, theropod dinosaur from the Late Cretaceous of Argentina....
. Zheng and colleagues also noted that Tianyuraptor shares some features with the monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
subfamily
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Microraptorinae
Microraptorinae
Microraptorinae is a subfamily of Dromaeosauridae. Microraptorines were among the most primitive dromaeosaurids. They appeared 125 million years ago in China. Many may have been semi-arboreal gliders...
, though they went on to say that this mixture of features suggests a basal placement for Tianyuraptor within Microraptorinae, as evidenced by their phylogenetic analysis which indicated maximum parsimony
Maximum parsimony
Parsimony is a non-parametric statistical method commonly used in computational phylogenetics for estimating phylogenies. Under parsimony, the preferred phylogenetic tree is the tree that requires the least evolutionary change to explain some observed data....
in six of the 30 results recovered by the analysis. The authors then go on to suggest that since Tianyuraptor is considered a short-armed microraptorine, more derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
long-armed microraptorines might have independently evolved flight capability. However, it is also equally possible, as argued by Zheng et al., that Tianyuraptor may in fact be a basal member of a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
containing all other Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n dromaeosaurids with the exception of Microraptorinae. This is indicated by the other 24 out of 30 most parsimonious trees recovered from the analysis. The discovery of Tianyuraptor sheds new light on the early evolution of dromaeosaurs and further exemplifies the great diversity this group enjoyed at an early stage.
See also
- ParavesParavesParaves is a branch-based clade containing birds and other closely related dinosaurs. The paravians include the Avialae, including Archaeopteryx and modern birds, and the Deinonychosauria, which includes the dromaeosaurids and troodontids....
- TianyulongTianyulongTianyulong is a genus of heterodontosaurid ornithischian dinosaur. The only species is T. confuciusi, whose remains were discovered in Jianchang County, Western Liaoning Province, China...
– A heterodontosaurid with filament structures and a similar name. - AustroraptorAustroraptorAustroraptor was a genus of dromaeosaurid dinosaur that lived about 70 million years ago during the Cretaceous period in what is now modern Argentina. The type species for the genus, Austroraptor cabazai, was described in late 2008 by Fernando Novas of the Museo Argentino de Ciencias Naturales...
– An unenlagiine dromaeosaurid with even shorter arms.
External links
- http://fossil.wikia.com/wiki/File:Tianyuraptor_skeleton_1.png http://fossil.wikia.com/wiki/File:Tianyuraptor_skull.png Images of the holotypeHolotypeA 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...
.
