Eshanosaurus

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Eshanosaurus
Temporal range: Early Jurassic, 201.4–199.5  Ma
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Eshanosaurus.png
Holotype mandible
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Therizinosauria (?)
Genus: Eshanosaurus
Xu, Zhou & Clark, 2001
Type species
Eshanosaurus deguchiianus
Xu, Zhou & Clark, 2001

Eshanosaurus is a genus of a dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be a therizinosaurian, and if so the earliest known coelurosaur.

Contents

Discovery and naming

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 fossilized left lower jaw and teeth, was uncovered in the Dull Purplish Beds of the Lower Lufeng Formation in Yunnan, dating to 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. [1]

Classification

Diagram of the holotype Eshanosaurus IVPP V11579.png
Diagram of the holotype

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 maniraptoran living long before Archaeopteryx , 60 million years before certain basal therizinosaurs such as Falcarius and Beipiaosaurus . A cladistic analysis was not performed and the authors "speculatively" suggested it was the most basal known therizinosauroid. [1] Due to the unusually long chronological gap in the therizinosauroid and coelurosaurian 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. [2] 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. [1]

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. [3]

In the second edition of the popular book The Princeton Field Guide to Dinosaurs, published in 2016, Gregory S. Paul suggested that Eshanosaurus may be closely related to the mysterious Chilesaurus , but without detailed comments.

See also

Related Research Articles

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<span class="mw-page-title-main">Therizinosauria</span> Extinct clade of dinosaurs

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<i>Lukousaurus</i> Extinct species of reptile

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<i>Neimongosaurus</i> Extinct genus of dinosaurs

Neimongosaurus is a genus of herbivorous therizinosaur theropod dinosaur that lived in Asia during the Cenomanian stage of the Late Cretaceous period in what is now the Iren Dabasu Formation.

<span class="mw-page-title-main">Heterodontosauridae</span> Extinct family of dinosaurs

Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group Genasauria. Although their fossils are relatively rare and their group small in numbers, they have been found on all continents except Australia and Antarctica, with a range spanning the Early Jurassic to the Early Cretaceous.

The Lufeng Formation is a Lower Jurassic sedimentary rock formation found in Yunnan, China. It has two units: the lower Dull Purplish Beds/Shawan Member are of Hettangian age, and Dark Red Beds/Zhangjia'ao Member are of Sinemurian age. It is known for its fossils of early dinosaurs. The Dull Purplish Beds have yielded the possible therizinosaur Eshanosaurus, the possible theropod Lukousaurus, and the "prosauropods" "Gyposaurus" sinensis, Lufengosaurus, Jingshanosaurus, and Yunnanosaurus. Dinosaurs discovered in the Dark Red Beds include the theropod Sinosaurus triassicus, the "prosauropods" "Gyposaurus", Lufengosaurus, and Yunnanosaurus, indeterminate remains of sauropods, and the early armored dinosaurs Bienosaurus and Tatisaurus.

<i>Platyognathus</i> Extinct genus of reptiles

Platyognathus is an extinct genus of protosuchian crocodylomorph. Fossils are known from the Early Jurassic Lower Lufeng Formation in Yunnan, China and belong to the type and only species, P. hsui.

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<span class="mw-page-title-main">Timeline of therizinosaur research</span>

The timeline of therizinosaur research is a chronological listing of events in the history of paleontology focused on therizinosaurs. They were unusually long-necked, pot-bellied, and large-clawed herbivorous theropods most closely related to birds. The early history of therizinosaur research occurred in three phases. The first phase was the discovery of scanty and puzzling fossils in Asia by the Central Asiatic Expeditions of the 1920s and Soviet-backed research in the 1950s. This phase resulted in the discovery of the Therizinosaurus cheloniformis type specimen. Soviet paleontologist Evgeny Maleev interpreted these unusual remains as belonging to some kind of gigantic turtle.

<i>Xingxiulong</i> Extinct genus of reptiles

Xingxiulong is a genus of bipedal sauropodiform from the Early Jurassic of China. It contains a single species, X. chengi, described by Wang et al. in 2017 from three specimens, two adults and an immature individual, that collectively constitute a mostly complete skeleton. Adults of the genus measured 4–5 metres (13–16 ft) long and 1–1.5 metres tall. Phylogenetic analysis suggests that Xingxiulong is most closely related to its contemporary Jingshanosaurus, although an alternative position outside of both the Sauropodiformes and Massospondylidae is also plausible.

References

  1. 1 2 3 Xu, X.; Zhao, X.; Clark, J. M. (2001). "A new therizinosaur from the Lower Jurassic lower Lufeng Formation of Yunnan, China". Journal of Vertebrate Paleontology. 21 (3): 477−483. doi:10.1671/0272-4634(2001)021[0477:ANTFTL]2.0.CO;2. JSTOR   20061976. S2CID   131298010.
  2. Kirkland, J. I.; Wolfe, D. G. (2001). "First definitive therizinosaurid (Dinosauria; Theropoda) from North America". Journal of Vertebrate Paleontology. 21 (3): 410−414. doi:10.1671/0272-4634(2001)021[0410:fdtdtf]2.0.co;2. JSTOR   20061971. S2CID   85705529.
  3. Barrett, P. M. (2009). "The affinities of the enigmatic dinosaur Eshanosaurus deguchiianus from the Early Jurassic of Yunnan Province, People's Republic of China". Palaeontology. 52 (4): 681−688. doi:10.1111/j.1475-4983.2009.00887.x.

Further reading