Aurornis

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Aurornis
Temporal range: Late Jurassic, 160Ma
Life restoration
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Avialae
Genus:Aurornis
Godefroit et al., 2013
Type species
Aurornis xui
Godefroit et al., 2013
 
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Aurornis
Temporal range: Late Jurassic, 160Ma
Life restoration
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Avialae
Genus:Aurornis
Godefroit et al., 2013
Type species
Aurornis xui
Godefroit et al., 2013

Aurornis is an extinct genus of dinosaurs from the Jurassic period of China. The genus Aurornis contains a single known species, Aurornis xui /aʊərˈɒrnɪs ˈʃ./.[1] Aurornis xui may be the most basal ("primitive") avialan dinosaurs known to date, and it is one of the earliest avialan found to date. The fossil evidence for the animal pre-dates that of the famous Archaeopteryx lithographica, often considered the earliest bird species, by about 10 million years.[1][2]

Aurornis xui was first described and named by Pascal Godefroit, Andrea Cau, Hu Dong-Yu, François Escuillié, Wu Wenhao and Gareth Dyke in 2013. The generic name is derived from the Latin word aurora, meaning "daybreak" or "dawn", and the Ancient Greek ὄρνις (órnis) meaning "bird". The specific name, A. xui, honors Xu Xing.[1]

Description[edit]

Aurornis was roughly the size of a modern pheasant – 50 cm (20 in) in length from beak to tail tip. It had claws and a long tail. Its leg bones are similar to those of Archaeopteryx, but overall its bone structure is more primitive.[2] The absence of larger feathers suggests A. xui was unable to fly. Aurornis lived roughly 160 million years ago, roughly 10 million years prior to Archaeopteryx, which often has been described as the first bird.[2]

Discovery[edit]

Aurornis was described from a sedimentary rock fossil in 2013. The fossil was purchased from a local dealer who said it had been unearthed in Yaoluguo in western Liaoning, China. Subsequent analysis confirmed it came from the Tiaojishan Formation, which has been dated to the late Jurassic period (Oxfordian stage), approximately 160 million years ago.[1][3][4] The fossil features traces of downy feathers along the animal's tail, chest, and neck. It was only partially prepared at the time of purchase with the feathers not showing, and bore no signs of forgery.[2]

On 7th June 2013, however, Science Magazine published an article which noted that Pascal Godefroit, the paleontologist who led the team that described Aurornis, reported that he is uncertain if the fossil material came from Liaoning province’'s 160-million-year-old Tiaojishan Formation, as the information provided by the fossil dealer indicated, or from the province’'s 125-million-year-old Yixian Formation, which is known to have produced several ancient bird fossils.[5] The failure to secure rigorous provenance information casts doubt on the claim that Aurornis is 160 million years old and predates Archaeopteryx. Godefroit's team will attempt to confirm the specimen’'s provenance, and its age, by conducting mineralogical and botanical analysis on the shale slab and then publishing their findings.

Classification[edit]

A phylogenetic analysis of Aurornis published in 2013 found that it belongs in the bird lineage, in a more basal position than Archaeopteryx.[2] The analysis was based on "almost 1,500 [anatomical] characteristics."[6]

The classification of A. xui as a bird is somewhat contentious, however, due to the various differing definitions of the word "bird". Recent discoveries "[emphasize] how grey the dividing line is between birds and [non-avian] dinosaurs", says Paul Barrett of the Natural History Museum in London. "There's such a gradation in features between them that it's very difficult to tell them apart ... [Aurornis xui] is certainly an older member of the bird lineage than Archaeopteryx, and it's fair to call it a very primitive bird. But what you call a bird comes down to what you call a bird, and a lot of definitions depend on Archaeopteryx."[2] Bird evolution specialist Lawrence Witmer called the new analysis compelling, but said it remains difficult to distinguish birds from birdlike dinosaurs: "All of these little feathered species running and flapping around ... were all very similar."[7]

American paleontologist Luis Chiappe said that A. xui's forelimb is too short to be a true bird. It "is very birdlike, but it is not yet a bird," he concluded.[8]

References[edit]

  1. ^ a b c d Godefroit, Pascal; Cau, Andrea; Hu, Dong-Yu; Escuillié, François; Wu, Wenhao; Dyke, Gareth (2013). "A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds". Nature. in press. doi:10.1038/nature12168.  edit
  2. ^ a b c d e f Ian Sample (May 29, 2013). "Early bird called Dawn beat Archaeopteryx to worm by 10m years". The Guardian. Retrieved May 29, 2013. 
  3. ^ Hu, D.; Hou, L.; Zhang, L. & Xu, X. (2009). "A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus". Nature 461 (7264): 640–643. Bibcode:2009Natur.461..640H. doi:10.1038/nature08322. PMID 19794491. 
  4. ^ Liu Y.-Q.; Kuang H.-W.; Jiang X.-J.; Peng N.; Xu H.; Sun H.-Y. (2012). "Timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the Jehol Biota". Palaeogeography, Palaeoclimatology, Palaeoecology. 323–325: 1–12. doi:10.1016/j.palaeo.2012.01.017. 
  5. ^ Michael Balter (2013) Authenticity of China's Fabulous Fossils Gets New Scrutiny. Science 340 (6137): 1153-1154 doi:10.1126/science.340.6137.1153
  6. ^ Jonathan Amos (May 29, 2013). "Archaeopteryx restored in fossil reshuffle". BBC. Retrieved May 29, 2013. 
  7. ^ "Dinosaur or bird? New study restores famed fossil to 'bird' branch". Fox News. Associated Press. May 29, 2013. Retrieved May 29, 2013. 
  8. ^ Rachel Ehrenberg (May 29, 2013). "Fossil muddies the origin of birds". Science News. Retrieved May 29, 2013. 

External links[edit]