Eshanosaurus
Encyclopedia
Eshanosaurus is a possible genus
of therizinosaur
ian dinosaur
from the early Jurassic
Period. It is known only from a partial lower jawbone. The fossil was found in China
. It may be the earliest known coelurosaur.
discovered a dinosaur fossil at Dianchung in Eshan county.
The type species
, Eshanosaurus deguchiianus, was described by Xu Xing, Zhao, and James M. Clark in 2001. The generic name is derived from Eshan. The specific name honours Hikaru Deguchi who convinced Xu that he should study dinosaurs. The type specimen, consisting of three fragments of a fossil
ized left lower jaw and teeth, was uncovered in the Dull Purplish Beds of the Lower Lufeng Formation in Yunnan
, dating to about 196 million years ago (Hettangian
stage). The specimen is in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology
in Beijing
, where it is catalogued under accession number IVPP V11579.
n living long before Archaeopteryx
, 60 million years before certain basal therizinosaur
s such as Falcarius
and Beipiaosaurus
. A cladistic analysis was not performed and the authors "speculatively" suggested it was the most basal known therizinosauroid. Due to the unusually long chronological gap in the therizinosauroid and coelurosauria
n fossil record or ghost lineage
created by this interpretation of the find, a few scientists have expressed doubts about the classification of Eshanosaurus as a therizinosauroid. James Kirkland and D.G. Wolfe, in their 2001 paper describing the therizinosaur Nothronychus
, related personal correspondence that the teeth of Eshanosaurus bore a medial ridge only seen in prosauropods or basal Sauropodomorpha
. Xu, Zhao and Clark, however, had examined the possibility that Eshanosaurus was a prosauropod, given that it was found below numerous fossils of Lufengosaurus
, a prosauropod of which the lower jaw closely resembles in general shape that of a therizinosaur. The authors arrived at their conclusion that the specimen represented an Early Jurassic therizinosauroid, by testing the possibility that it were a basal sauropodomorph as rigorously as they could using the comparative method: the six traits found were those shared between Eshanosaurus and therizinosaurs to the exclusion of prosauropods.
In 2009, a paper published by Paul M. Barrett again examined the question of Eshanosaurus classification. Barrett examined the type specimen in detail, noting six features shared with therizinosaurs but not shown by prosauropods. Barrett concluded by agreeing with the original interpretation, that Eshanosaurus is a therizinosaur, and that its presence in the early Jurassic has important implications for the evolutionary history of coelurosaurs, notably, that large portions of the coelurosaur fossil record remain missing.
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 therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
ian 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...
from the early Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
Period. It is known only from a partial lower jawbone. The fossil was found in 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 may be the earliest known coelurosaur.
Discovery and naming
In 1971 Zhao XijinZhao Xijin
Zhao Xijin is a Chinese paleontologist. He is notable for having named numerous dinosaurs. He is currently a professor at Beijing's Institute of Vertebrate Paleontology and Paleoanthropology.-Career:...
discovered a dinosaur fossil at Dianchung in Eshan county.
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...
, Eshanosaurus deguchiianus, was described by Xu Xing, Zhao, and James M. Clark in 2001. The generic name is derived from Eshan. The specific name honours Hikaru Deguchi who convinced Xu that he should study dinosaurs. The type specimen, consisting of three fragments of a fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized left lower jaw and teeth, was uncovered in the Dull Purplish Beds of the Lower Lufeng Formation in Yunnan
Yunnan
Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...
, dating to about 196 million years ago (Hettangian
Hettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
stage). The specimen is in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology
Institute of Vertebrate Paleontology and Paleoanthropology
The Institute of Vertebrate Paleontology and Paleoanthropology of China is a prominent research institution and collections repository for fossils, including many dinosaur and pterosaurand cat poo specimens...
in Beijing
Beijing
Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...
, where it is catalogued under accession number IVPP V11579.
Classification
The authors who initially described the fossil, classified Eshanosaurus as a member of the Therizinosauroidea on the basis of six distinct characteristics of the jaw and teeth, making it the earliest known coelurosaur, a maniraptoraManiraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n living long before Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, 60 million years before certain basal therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s such as Falcarius
Falcarius
Falcarius is a genus of therizinosaurian dinosaur found in east-central Utah, United States. Its name is derived from the word sickle , which scientists have used to describe its unwieldy clawed hands...
and Beipiaosaurus
Beipiaosaurus
Beipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China.The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical...
. A cladistic analysis was not performed and the authors "speculatively" suggested it was the most basal known therizinosauroid. Due to the unusually long chronological gap in the therizinosauroid and coelurosauria
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...
n fossil record or ghost lineage
Ghost lineage
A ghost lineage is a phylogenetic lineage that is inferred to exist but has no fossil record....
created by this interpretation of the find, a few scientists have expressed doubts about the classification of Eshanosaurus as a therizinosauroid. James Kirkland and D.G. Wolfe, in their 2001 paper describing the therizinosaur Nothronychus
Nothronychus
Nothronychus is a genus of theropod dinosaur classified in the group Therizinosauria, from the Cretaceous of North America.The type species of this dinosaur, Nothronychus mckinleyi, was described by James Kirkland and Douglas G. Wolfe in 2001...
, related personal correspondence that the teeth of Eshanosaurus bore a medial ridge only seen in prosauropods or basal Sauropodomorpha
Sauropodomorpha
Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The...
. Xu, Zhao and Clark, however, had examined the possibility that Eshanosaurus was a prosauropod, given that it was found below numerous fossils of Lufengosaurus
Lufengosaurus
Lufengosaurus is a genus of prosauropod dinosaur which lived during the Early Jurassic period in what is now southwestern China.-Discovery and species:...
, a prosauropod of which the lower jaw closely resembles in general shape that of a therizinosaur. The authors arrived at their conclusion that the specimen represented an Early Jurassic therizinosauroid, by testing the possibility that it were a basal sauropodomorph as rigorously as they could using the comparative method: the six traits found were those shared between Eshanosaurus and therizinosaurs to the exclusion of prosauropods.
In 2009, a paper published by Paul M. Barrett again examined the question of Eshanosaurus classification. Barrett examined the type specimen in detail, noting six features shared with therizinosaurs but not shown by prosauropods. Barrett concluded by agreeing with the original interpretation, that Eshanosaurus is a therizinosaur, and that its presence in the early Jurassic has important implications for the evolutionary history of coelurosaurs, notably, that large portions of the coelurosaur fossil record remain missing.
External links
- http://www.thescelosaurus.com/dinosauromorpha.htm
- http://www.dinosauria.com/dml/names/dinoe.htm