Epidexipteryx

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Epidexipteryx
Temporal range: Middle or Late Jurassic, 164Ma
↓
Life restoration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Theropoda
Family: †Scansoriopterygidae
Genus: †Epidexipteryx
Zhang et al., 2008
Type species
†Epidexipteryx hui
Zhang et al., 2008

Epidexipteryx ("display feather") is a genus of small paravian dinosaur, known from one fossil specimen in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. Epidexipteryx represents the earliest known example of ornamental feathers in the fossil record.[1] The type specimen is catalog number IVPP V 15471. It has been reported to be a maniraptoran dinosaur from the Middle Jurassic or Upper Jurassic age Daohugou Beds of Inner Mongolia, China (about 160 or 168 mya).[2]

The specific name, Epidexipteryx hui ("Hu's display feather"), and its Chinese name Hushi Yaolong ("Hu Yaoming's dragon") were coined in memory of paleomammologist Hu Yaoming.[3]

History of publication

Due to a pre-publication error,[4] a manuscript of the Epidexipteryx hui description first appeared on a preprint Web portal in late September, 2008. The paper was officially published in the October 23rd, 2008, issue of the journal Nature.[2]

Taxonomy and systematics

The exact phylogenetic position of Epidexipteryx within Paraves is uncertain. The phylogenetic analysis conducted by the authors of its description recovered it as a member of the family Scansoriopterygidae and as a basal member of the clade Avialae;[2] this was confirmed by the subsequent analysis conducted by Hu et al. (2009).[5] A later analysis conducted by Agnolín and Novas (2011) confirmed it to be a scansoriopterygid, but recovered a different phylogenetic position of this family: Scansoriopterygidae was recovered in polytomy with the family Alvarezsauridae and the clade Eumaniraptora (containing the clades Avialae and Deinonychosauria).[6] Turner, Makovicky and Norell (2012) included Epidexipteryx but not Scansoriopteryx/Epidendrosaurus in their primary phylogenetic analysis, as a full-grown specimen is known only of the former taxon; regarding Scansoriopteryx/Epidendrosaurus, the authors were worried that including it in the primary analysis would be problematic, because it is only known from juvenile specimens, which "do not necessarily preserve all the adult morphology needed to accurately place a taxon phylogenetically" (Turner, Makovicky and Norell 2012, p. 89). Epidexipteryx was recovered as basal paravian that didn't belong to Eumaniraptora. The authors did note that its phylogenetic position is unstable; constraining Epidexipteryx hui as a basal avialan required two additional steps compared to the most parsimonious solution, while constraining it as a basal member of Oviraptorosauria required only one additional step. A separate exploratory analysis included Scansoriopteryx/Epidendrosaurus, which was recovered as a basal member of Avialae; the authors noted that it did not clade with Epidexipteryx, which stayed outside Eumaniraptora. Constraining the monophyly of Scansoriopterygidae required four additional steps and moved Epidexipteryx into Avialae.[7] A monophyletic Scansoriopterygidae was recovered by Godefroit et al. (2013); the authors found scansoriopterygids to be basalmost members of Paraves and the sister group to the clade containing Avialae and Deinonychosauria.[8] Agnolín and Novas (2013) recovered monophyletic Scansoriopterygidae as well, but found them to be non-paravian maniraptorans and the sister group to Oviraptorosauria.[9]

Description

It is known from a well preserved partial skeleton that includes four long feathers on the tail, composed of a central rachis and vanes. However, unlike in modern-style rectrices (tail feathers), the vanes were not branched into individual filaments but made up of a single ribbon-like sheet. Epidexipteryx also preserved a covering of simpler body feathers, composed of parallel barbs as in more primitive feathered dinosaurs. However, the body feathers of Epidexipteryx are unique in that some appear to arise from a "membranous structure"[2] at the base of each feather. It has been suggested that this may represent a stage in the evolution of the feather.[10]

Size of E. hui (green) compared to a human

In all, the skeleton of Epidexipteryx hui measures 25 centimeters (10 inches) in length (44.5 cm or 17.5 in including the incomplete tail feathers),[11] and the authors estimated a weight of 164 grams, smaller than most other basal avialans.[2]

The skull of Epidexipteryx is also unique in a number of features, and bears an overall similarity to the skull of Sapeornis, oviraptorosaurs and, to a lesser extent, therizinosauroids. It had teeth only in the front of the jaws, with unusually long front teeth angled forward, a feature only seen in Masiakasaurus among other theropods. The rest of the skeleton bore an overall similarity to the possibly closely related Scansoriopteryx, including a hip configuration unusual among other dinosaurs: the pubis was shorter than the ischium, and the ischium itself was expanded towards the tip. The tail of Epidexipteryx also bore unusual vertebrae towards the tip which resembled the feather-anchoring pygostyle of modern birds and some oviraptorosaurs.[2]

Epidexipteryx appears to have lacked remiges (wing feathers), and it likely could not fly. Zhang et al. suggest that unless Epidexipteryx evolved from flying ancestors and subsequently lost its wings, this may indicate that advanced display feathers on the tail may have predated flying or gliding flight.[2]

References

  1. ↑ Morgan, James (2008-10-22). "New feathered dinosaur discovered". BBC. Retrieved 2009-07-02. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Zhang, Fucheng; Zhou, Zhonghe; Xu, Xing; Wang, Xiaolin and Sullivan, Corwin. "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers". <http://www.nature.com/nature/journal/v455/n7216/full/nature07447.html> Nature 455, 1105-1108 (23 October 2008) | doi:10.1038/nature07447 PMID 18948955
  3. ↑ "Chinese scientists discovers new dinosaur species". People's Daily Online. 15:26, October 27, 2008. Retrieved November 4, 2008. 
  4. ↑ Dr. Thomas Holtz, Jr. "The mistaken scansoripterygid". Message to the Dinosaur Mailing List <http://dml.cmnh.org/2008Oct/msg00008.html> (October 1, 2008)
  5. ↑ Dongyu Hu, Lianhai Hou, Lijun Zhang and Xing Xu (2009). "A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus". Nature 461 (7264): 640–643. doi:10.1038/nature08322. PMID 19794491. 
  6. ↑ Agnolín, Federico L.; Novas, Fernando E. (2011). "Unenlagiid theropods: are they members of the Dromaeosauridae (Theropoda, Maniraptora)?". Anais da Academia Brasileira de Ciências 83 (1): 117–162. doi:10.1590/S0001-37652011000100008. 
  7. ↑ Alan Hamilton Turner, Peter J. Makovicky and Mark Norell (2012). "A review of dromaeosaurid systematics and paravian phylogeny". Bulletin of the American Museum of Natural History 371: 1–206. doi:10.1206/748.1. 
  8. ↑ Pascal Godefroit, Helena Demuynck, Gareth Dyke, Dongyu Hu, François Escuillié and Philippe Claeys (2013). "Reduced plumage and flight ability of a new Jurassic paravian theropod from China". Nature Communications 4: Article number 1394. doi:10.1038/ncomms2389. PMID 23340434. 
  9. ↑ Federico L. Agnolín and Fernando E. Novas (2013). "Avian ancestors. A review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, Anchiornis and Scansoriopterygidae". SpringerBriefs in Earth System Sciences: 1–96. doi:10.1007/978-94-007-5637-3. 
  10. ↑ http://scienceblogs.com/tetrapodzoology/2008/10/epidexipteryx_at_last.php
  11. ↑ Zhang, F., Zhou, Z., Xu, X., Wang, X. and Sullivan, C. (2008). "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers", Supplementary Information. Nature, 455: 46pp. doi:10.1038/nature07447 PMID 18948955

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