The possibility that dinosaurs are closely related to birds raised the possibility of feathers. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-bird dinosaur fossils were discovered with preserved feathers. About 40 genera of theropods are now known to be feathered.
Most of these fossils come from the Yixian formation in China. The fossil feathers of one specimen, Shuvuuia deserti, have been tested positive for beta-keratin in immunological tests.[1] This is the main protein in bird feathers.
After a century without clear evidence, well-preserved fossils of feathered dinosaurs were discovered during the 1990s, and more continue to be found. The fossils were preserved in a Lagerstätte — a sedimentary deposit exhibiting remarkable richness and completeness in its fossils — in Liaoning, China.
The most important discoveries at Liaoning have been a host of feathered dinosaur fossils, with a steady stream of new finds filling in the picture of the dinosaur-bird connection and adding more to theories of the evolutionary development of feathers and flight. Quill knobs were found an ulna of Velociraptor mongoliensis. These are associated with large, well-developed secondary feathers.[2]
Behavioural evidence, in the form of an oviraptorosaur on its nest, showed another link with birds. Its forearms were folded, like those of a bird.[3] Although no feathers were preserved, it is likely that these would have been present to keep eggs and juveniles warm.[4]
The feathered tail of a non-avialan (non-bird) theropod has been found preserved in mid-Cretaceous (∼99 mya) amber from Kachin State, Myanmar (Burma).[5] The BBC describe it as "perfectly preserved".[6] Lida Xing found it at an amber market in Myitkina, Myanmar. The amber was already polished for jewellery: the seller thought it was plant material. However, it was the tail of a feathered dinosaur about the size of a sparrow. The feathers were not flight feathers. Dr Paul Barrett, from London's Natural History Museum, called the specimen a "beautiful fossil", describing it as a "really rare occurrence of vertebrate material in amber".[6]
In 2011, samples of amber were discovered to contain preserved feathers from the Cretaceous period, with evidence that they were from both dinosaurs and birds. Initial analysis suggests that some of the feathers were used for insulation, and not flight.[7][8]
Many non-avialan dinosaurs are now known to have been feathered. Direct evidence of feathers exists for the following genera, listed in the order of when the evidence was first published.
The evidence consists of feather impressions, or convincing skeletal or chemical evidence. Skeletal evidence would be the presence of quill knobs (the anchor points for wing feathers on the forelimb) or a pygostyle (the fused vertebrae at the tail tip which often supports large feathers).
For comparison: Archaeopteryx (1861; avialan)[9][10] definitely had working flight feathers with off-centre rachis (stem). Otherwise, apart from the front limbs, it was a typical small carnivorous dinosaur.
Note, filamentous structures in some ornithischian dinosaurs (Psittacosaurus, Tianyulong) and pterosaurs may or may not be homologous with the feathers and protofeathers of theropods.[37][51]
↑Hopp, Thomas J. & Orsen, Mark J. 2004. In Philip J. Currie, Eva B. Koppelhus and Martin A. Shugar (eds) Feathered Dragons: studies on the transition from dinosaurs to birds. Chapter 11: Dinosaur brooding behavior and the origin of flight feathers. Indiana University Press. Bloomington IN. USA.
↑Lida Xing et al 2016. A feathered dinosaur tail with primitive plumage trapped in mid-Cretaceous amber. Current Biology. [1]
↑ 6.06.1Rincon, Paul 2016. 'Beautiful' dinosaur tail found preserved in amber. BBC News Science & Environment. [2]
↑von Meyer H. 1861. Archaeopteryx litographica (Vogel-Feder) und Pterodactylus von Solenhofen. Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde. 1861: 678–679, plate V [Article in German] Fulltext at Google Books.
↑Kurzanov S.M. 1987. Avimimidae and the problem of the origin of birds. Transactions of the Joint Soviet-Mongolian Paleontological Expedition, 31: 5-92. [in Russian]
↑Chiappe L.M. and Witmer L.M. 2002. Mesozoic Birds: above the heads of dinosaurs. Berkeley: University of California Press. ISBN0-520-20094-2
↑Ji Q., Ji S. (1996). "On discovery of the earliest bird fossil in China and the origin of birds". Chinese Geology. 10 (233): 30–33.
↑Ji, Q. and Ji, S. 1997. A Chinese archaeopterygian, Protarchaeopteryx gen. nov." Geological Science and Technology (Di Zhi Ke Ji), 238: 38-41. Translated By Will Downs Bilby Research Center Northern Arizona University January 2001
↑Ji, Q.; Ji, S. (1997). "Advances in Sinosauropteryx research". Chinese Geology. 7: 30–32.
↑Czerkas S.A. and Yuan C. 2002. An arboreal maniraptoran from northeast China. In Czerkas S.J. (ed) Feathered dinosaurs and the origin of flight, 63-95. The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A. PDF abridged version
↑Xu X., Wang X.-L. (2003). "A new maniraptoran from the early Cretaceous Yixian Formation of western Liaoning". Vertebrata PalAsiatica. 41 (3): 195–202.
↑Ji S.; et al. (2007). "A new giant compsognathid dinosaur with long filamentous integuments from Lower Cretaceous of Northeastern China". Acta Geologica Sinica. 81 (1): 8–15.
↑Zhang, Fucheng; et al. (2008). "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers". Nature. 455 (7216): 1105–1108. doi:10.1038/nature07447. PMID18948955. S2CID4362560.
↑He T.; Wang X.L; Zhou Z.H (2008). "A new genus and species of caudipterid dinosaur from the Lower Cretaceous Jiufotang Formation of western Liaoning, China". Vertebrata PalAsiatica. 46 (3): 178–189.
↑Gao, Cunling et al (2008) A new basal lineage Of early Cretaceous birds from China and its implications on the evolution of the avian tail. Palaeontology51, Part 4, pp. 775-791. doi:10.1111/j.1475-4983.2008.00793.x
↑En-Pu Gong; et al. (2012). "A new species of Microraptor from the Jehol Biota of northeastern China". Palaeoworld. 21 (2): 81–91. doi:10.1016/j.palwor.2012.05.003.
↑Ji Qiang; et al. (2012). "A new oviraptorosaur from the Yixian Formation of Jianchang, Western Liaoning Province, China". Regional Geology of China (12): 2102–2107.
↑Pascal Godefroit; et al. (2013). "A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds". Nature. 498 (7454): 359–362. doi:10.1038/nature12168. PMID23719374. S2CID4364892.
↑Yuong-Nam Lee; et al. (2014). "Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus". Nature. 515 (7526): 257–260. doi:10.1038/nature13874. PMID25337880. S2CID2986017.
↑Xu, X. et al 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature. [3]
↑Czerkas S.A., and Ji Q. 2002. A new rhamphorhynchoid with a headcrest and complex integumentary structures. Pp. 15-41 in: Czerkas, S.J. (Ed.). Feathered dinosaurs and the origin of flight. Blanding, Utah: The Dinosaur Museum. ISBN1-932075-01-1.