Although growing evidence of the relationship of non-avian dinosaurs to birds raised the possibility of feathered dinosaurs over the twentieth century, it was not until the mid-1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers. Since then, feathers or feather-like integument have been discovered on dozens of genera of dinosaurs via both direct and indirect fossil evidence. The fossil feathers of one specimen of the alvarezsaurid Shuvuuia deserti have tested positive for beta-keratin, the main protein in bird feathers. Although the vast majority of feather discoveries have been for coeleurosaurian theropods, the discoveries of integument on a megalosauroid theropod and on at least three ornithschians raise the likelihood that proto-feathers were present in basal dinosaurs, and perhaps even a more ancestral animal, in light of the pycnofibers of pterosaurs.
History of research
Shortly after the 1859 publication of Charles Darwin's On the Origin of Species, British biologist Thomas Henry Huxley proposed that birds were descendants of dinosaurs. He compared the skeletal structure of Compsognathus, a small theropod dinosaur, and the 'first bird' Archaeopteryx lithographica (both of which were found in the Upper Jurassic Bavarian limestone of Solnhofen). He showed that, apart from its hands and feathers, Archaeopteryx was quite similar to Compsognathus. Thus Archaeopteryx represents a transitional fossil. In 1868 he published On the Animals which are most nearly intermediate between Birds and Reptiles, making the case. The leading dinosaur expert of the time, Richard Owen, disagreed, claiming Archaeopteryx as the first bird outside dinosaur lineage. For the next century, claims that birds were dinosaur descendants faded, with more popular bird-ancestry hypotheses including 'crocodylomorph' and 'thecodont' ancestors, rather than dinosaurs or other archosaurs.
In 1964, John Ostrom described Deinonychus antirrhopus, a theropod whose skeletal resemblance to birds seemed unmistakable. Ostrom became a leading proponent of the theory that birds are direct descendants of dinosaurs. Further comparisons of bird and dinosaur skeletons, as well as cladistic analysis strengthened the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include the neck, the pubis, the wrists (semi-lunate carpal), the 'arms' and pectoral girdle, the shoulder blade, the clavicle and the breast bone. In all, over a hundred distinct anatomical features are shared by birds and theropod dinosaurs.
Other researchers drew on these shared features and other aspects of dinosaur biology and began to suggest that at least some theropod dinosaurs were feathered. The first restoration of a feathered dinosaur was Sarah Landry's depiction of a feathered "Syntarsus" (now renamed Megapnosaurus or considered a synonym of Coelophysis), in Robert T. Bakker's 1975 publication Dinosaur Renaissance. Gregory S. Paul was probably the first paleoartist to depict maniraptoran dinosaurs with feathers and protofeathers, starting in the late 1970s.
By the 1990s, most paleontologists considered birds to be surviving dinosaurs and referred to 'non-avialan dinosaurs' (all extinct), to distinguish them from birds (Avialae). Before the discovery of feathered dinosaurs, the evidence was limited to Huxley and Ostrom's comparative anatomy. Some mainstream ornithologists, including Smithsonian Institution curator Storrs L. Olson, disputed the links, specifically citing the lack of fossil evidence for feathered dinosaurs.
After a century of hypotheses without conclusive 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 area had repeatedly been smothered in volcanic ash produced by eruptions in Inner Mongolia 124 million years ago, during the Early Cretaceous epoch. The fine-grained ash preserved the living organisms that it buried in fine detail. The area was teeming with life, with millions of leaves, angiosperms (the oldest known), insects, fish, frogs, salamanders, mammals, turtles, and lizards discovered to date.
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. Turner et al. (2007) reported quill knobs from an ulna of Velociraptor mongoliensis, and these are strongly correlated with large and well-developed secondary feathers.
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. Although no feathers were preserved, it is likely that these would have been present to insulate eggs and juveniles.
Not all of the Chinese fossil discoveries proved valid however. In 1999, a supposed fossil of an apparently feathered dinosaur named "Archaeoraptor liaoningensis", found in Liaoning Province, northeastern China, turned out to be a forgery. Comparing the photograph of the specimen with another find, Chinese paleontologist Xu Xing came to the conclusion that it was composed of two portions of different fossil animals. His claim made National Geographic review their research and they too came to the same conclusion. The bottom portion of the "Archaeoraptor" composite came from a legitimate feathered dromaeosaurid now known as Microraptor, and the upper portion from a previously-known primitive bird called Yanornis.
Analysis of the ichthyosaur SMF 457 shows that during the degradation of collagen fibers, mineralization progresses from the inner part of the fiber bundle to the outer, resulting in lighter and darker regions similar to that found in Sinosauropteryx.
In 2011, samples of amber were discovered to contain preserved feathers from 75 to 80 million years ago during the Cretaceous era, 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. More complex feathers were revealed to have variations in coloration similar to modern birds, while simpler protofeathers were predominantly dark. Only 11 specimens are currently known. The specimens are too rare to be broken open to study their melanosomes, but there are plans for using non-destructive high-resolution X-ray imaging.
List of dinosaur species preserved with evidence of feathers
A number of non-avialan dinosaurs are now known to have been feathered. Direct evidence of feathers exists for the following species, listed in the order currently accepted evidence was first published. In all examples, the evidence described consists of feather impressions, except those genera inferred to have had feathers based on skeletal or chemical evidence, such as 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).
- Avimimus portentosus (inferred 1987: quill knobs)
- Pelecanimimus polydon? (1994)
- Sinosauropteryx prima (1996)
- Protarchaeopteryx robusta (1997)
- GMV 2124 (1997)
- Caudipteryx zoui (1998)
- Shuvuuia deserti (1999)
- Sinornithosaurus millenii (1999)
- Beipiaosaurus inexpectus (1999)
- Caudipteryx dongi (2000)
- Caudipteryx sp. (2000)
- Microraptor zhaoianus (2000)
- Nomingia gobiensis (inferred 2000: pygostyle)
- Psittacosaurus sp.? (2002)
- Yixianosaurus longimanus (2003)
- Dilong paradoxus (2004)
- Jinfengopteryx elegans (2005)
- Juravenator starki (2006)
- Sinocalliopteryx gigas (2007)
- Velociraptor mongoliensis (inferred 2007: quill knobs)
- Similicaudipteryx yixianensis (inferred 2008: pygostyle; confirmed 2010)
- Tianyulong confuciusi? (2009)
- Yutyrannus huali (2012)
- Microraptor hanqingi (2012)
- Sciurumimus albersdoerferi (2012)
- Ornithomimus edmontonicus (2012)
- Ningyuansaurus wangi (2012)
- Jianchangosaurus yixianensis (2013)
- Citipati osmolskae (inferred 2013: pygostyle)
- Conchoraptor gracilis (inferred 2013: pygostyle)
- Changyuraptor yangi (2014)
- Kulindadromeus zabaikalicus? (2014)
- Note that the filamentous structures in some ornithischian dinosaurs (Psittacosaurus, Tianyulong and Kulindadromeus) and the pycnofibres found in some pterosaurs may or may not be homologous with the feathers of theropods.
Primitive feather types
Integumentary structures that gave rise to the feathers of birds are seen in the dorsal spines of reptiles and fish. A similar stage in their evolution to the complex coats of birds and mammals can be observed in living reptiles such as iguanas and Gonocephalus agamids. Feather structures are thought to have proceeded from simple hollow filaments through several stages of increasing complexity, ending with the large, deeply rooted, feathers with strong pens (rachis), barbs and barbules that birds display today.
According to Prum's (1999) proposed model, at stage I, the follicle originates with a cylindrical epidermal depression around the base of the feather papilla. The first feather resulted when undifferentiated tubular follicle collar developed out of the old keratinocytes being pushed out. At stage II, the inner, basilar layer of the follicle collar differentiated into longitudinal barb ridges with unbranched keratin filaments, while the thin peripheral layer of the collar became the deciduous sheath, forming a tuft of unbranched barbs with a basal calamus. Stage III consists of two developmental novelties, IIIa and IIIb, as either could have occurred first. Stage IIIa involves helical displacement of barb ridges arising within the collar. The barb ridges on the anterior midline of the follicle fuse together, forming the rachis. The creation of a posterior barb locus follows, giving an indeterminate number of barbs. This resulted in a feather with a symmetrical, primarily branched structure with a rachis and unbranched barbs. In stage IIIb, barbules paired within the peripheral barbule plates of the barb ridges, create branched barbs with rami and barbules. This resulting feather is one with a tuft of branched barbs without a rachis. At stage IV, differentiated distal and proximal barbules produce a closed, pennaceous vane. A closed vane develops when pennulae on the distal barbules form a hooked shape to attach to the simpler proximal barbules of the adjacent barb. Stage V developmental novelties gave rise to additional structural diversity in the closed pennaceous feather. Here, asymmetrical flight feathers, bipinnate plumulaceous feathers, filoplumes, powder down, and bristles evolved.
Some evidence suggests that the original function of simple feathers was insulation. In particular, preserved patches of skin in large, derived, tyrannosauroids show scutes, while those in smaller, more primitive, forms show feathers. This may indicate that the larger forms had complex skins, with both scutes and filaments, or that tyrannosauroids may be like rhinos and elephants, having filaments at birth and then losing them as they developed to maturity. An adult Tyrannosaurus rex weighed about as much as an African Elephant. If large tyrannosauroids were endothermic, they would have needed to radiate heat efficiently, and feathers would have interfered with this.
There is now an increasing body of evidence that supports the display hypothesis, which states that early feathers were colored and increased reproductive success. Coloration could have provided the original adaptation of feathers, implying that all later functions of feathers, such as thermoregulation and flight, were co-opted. This hypothesis has been supported by the discovery of pigmented feathers in multiple species. Additionally, some specimens have iridescent feathers. Pigmented and iridescent feathers may have provided greater attractiveness to mates, providing enhanced reproductive success when compared to non-colored feathers. Current research shows that it is plausible that theropods would have had the visual acuity necessary to see the displays. In a study by Stevens (2006), the binocular field of view for Velociraptor has been estimated to be 55 to 60 degrees, which is about that of modern owls. Visual acuity for Tyrannosaurus has been predicted to be anywhere from about that of humans to 13 times that of humans. However, as both Velociraptor and Tyrannosaurus have a rather extended evolutionary relationship with the more basal theropods, it is unclear how much of this visual acuity data can be extrapolated.
The fact that precursors of feathers appeared and then were co-opted for insulation is already present in Gould and Vrba, 1982. The reason why such precursors appeared could be explained by a theory which is based on metabolic issue. Feathers are made of protein and contain substantial amounts of certain amino acids, especially cysteine. The protein complex at the base of the composition of the feather is keratin, which has disulfide bonds between amino acids that confer unique properties of stability and elasticity. The metabolism of amino acids containing sulfur proved to be toxic to the organism. If the sulfur amino acids are not catabolized at the final products of urea or uric acid but used for the synthesis of keratin instead, the release of hydrogen sulfide is extremely reduced or avoided. For an organism whose metabolism works at high internal temperatures of 40 °C or greater can be extremely important to prevent the excess production of hydrogen sulfide. This hypothesis could be consistent with the need for high metabolic rate of theropod dinosaurs.
It is not known with certainty at what point in archosaur phylogeny the earliest simple “protofeathers” arose, or whether they arose once or independently multiple times. Filamentous structures are clearly present in pterosaurs, and long, hollow quills have been reported in specimens of the ornithischian dinosaurs Psittacosaurus and Tianyulong. In 2009, Xu et al. noted that the hollow, unbranched, stiff integumentary structures found on a specimen of Beipiaosaurus were strikingly similar to the integumentary structures of Psittacosaurus and pterosaurs. They suggested that all of these structures may have been inherited from a common ancestor much earlier in the evolution of archosaurs, possibly in an ornithodire from the Middle Triassic or earlier. More recently, findings in Russia of the basal neornithischian Kulindadromeus report that although the lower leg and tail seemed to be scaled, "varied integumentary structures were found directly associated with skeletal elements, supporting the hypothesis that simple filamentous feathers, as well as compound feather-like structures comparable to those in theropods, were widespread amongst the whole dinosaur clade."
Display feathers are also known from dinosaurs that are very primitive members of the bird lineage, or Avialae. The most primitive example is Epidexipteryx, which had a short tail with extremely long, ribbon-like feathers. Oddly enough, the fossil does not preserve wing feathers, suggesting that Epidexipteryx was either secondarily flightless, or that display feathers evolved before flight feathers in the bird lineage. Plumaceous feathers are found in nearly all lineages of Theropoda common in the northern hemisphere, and pennaceous feathers are attested as far down the tree as the Ornithomimosauria. The fact that only adult Ornithomimus had wing-like structures suggests that pennaceous feathers evolved for mating displays.
Phylogeny and the inference of feathers in other dinosaurs
Fossil feather impressions are extremely rare and they require exceptional preservation conditions to form. Therefore only a few feathered dinosaur genera have been identified. However, these cover nearly all of the major groups of the theropods, though as of 2013 no feathered ceratosaurian has been discovered. (Ceratosaurians are mostly of the Southern Hemisphere, where no appropriately preserved fossil beds are known.) All fossil feather specimens have been found to show certain similarities. Due to these similarities and through developmental research, almost all scientists agree that feathers could only have evolved once in dinosaurs. Feathers would then have been passed down to all later, more derived species, unless some lineages lost feathers secondarily. If a dinosaur falls at a point on an evolutionary tree within the known feather-bearing lineages, then its ancestors had feathers, and it is quite possible that it did as well. This technique, called phylogenetic bracketing, can also be used to infer the type of feathers a species may have had, since the developmental history of feathers is now reasonably well-known. All feathered species had filamentaceous or plumaceous (downy) feathers, with pennaceous feathers found among the more bird-like groups. The following cladogram is adapted from Godefroit et al., 2013.
- Schweitzer, M.H.; Watt, J.A.; Avci, R.; Knapp, L.; Chiappe, L.; Norell, M.; Marshall, M. (1999). "Beta-keratin specific immunological reactivity in feather-like structures of the Cretaceous Alvarezsaurid,Shuvuuia deserti". Journal of Experimental Zoology 285 (2): 146–57. doi:10.1002/(SICI)1097-010X(19990815)285:2<146::AID-JEZ7>3.0.CO;2-A. PMID 10440726.
- Huxley, T.H. (1868). "On the animals which are most nearly intermediate between birds and reptiles". Annals and Magazine of Natural History. 4th 2: 66–75.
- Foster, Michael; Lankester, E. Ray 1898–1903. The scientific memoirs of Thomas Henry Huxley. 4 vols and supplement. London: Macmillan.
- Paul, Gregory S. (2000). "A Quick History of Dinosaur Art". In Paul, Gregory S. (ed.). The Scientific American Book of Dinosaurs. New York: St. Martin's Press. pp. 107–112. ISBN 0-312-26226-4.
- Turner, A.H.; Makovicky, P.J.; Norell, M.A. (2007). "Feather quill knobs in the dinosaur Velociraptor" (pdf). Science 317 (5845): 1721. Bibcode:2007Sci...317.1721T. doi:10.1126/science.1145076. PMID 17885130.
- Norell M.A., Clark J.M., Chiappe L.M., Dashzeveg D.; Clark; Chiappe; Dashzeveg (1995). "A nesting dinosaur". Nature 378 (6559): 774–776. Bibcode:1995Natur.378..774N. doi:10.1038/378774a0.
- Hopp, Thomas J., Orsen, Mark J. (2004) "Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. Chapter 11. Dinosaur Brooding Behavior and the Origin of Flight Feathers" Currie, Koppelhaus, Shugar, Wright. Indiana University Press. Bloomington, IN. USA.
- "Transcript: The Dinosaur that Fooled the World". BBC. Retrieved 22 December 2006.
- Feduccia, A; Lingham-Soliar, T; Hinchliffe, JR (2005). "Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence". Journal of Morphology 266 (2): 125–166. doi:10.1002/jmor.10382. PMID 16217748.
- Emily Chung (12 September 2011). "Dinosaur feathers found in Alberta amber". CBC. Retrieved 16 September 2011.
- Brian Switek (15 September 2011). "Amber inclusions showcase prehistoric feathers". Nature News. doi:10.1038/news.2011.539. Retrieved 22 September 2011.
- 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, 536 pp. ISBN 0-520-20094-2
- Perez-Moreno B. P., Sanz J. L., Buscalioni A. D., Moratalla J. J., Ortega F., Raskin-Gutman D.; Luis Sanz; Buscalioni; Moratalla; Ortega; Rasskin-Gutman (1994). "A unique multitoothed ornithomimosaur from the Lower Cretaceous of Spain". Nature 370 (6488): 363–367. Bibcode:1994Natur.370..363P. doi:10.1038/370363a0.
- 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.
- Currie, Philip J.; Qiang, Ji; Norell, Mark A.; Shu-An, Ji (1998). "Two feathered dinosaurs from northeastern China". Nature 393 (6687): 753–761. Bibcode:1998Natur.393..753Q. doi:10.1038/31635.
- Wu, Xiao-Chun; Xu, Xing; Wang, Xiao-Lin (1999). "A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China". Nature 401 (6750): 262–266. Bibcode:1999Natur.401..262X. doi:10.1038/45769.
- Xu, Xing; Tang, Zhi-lu; Wang, Xiao-lin (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature 399 (6734): 350–354. Bibcode:1999Natur.399..350X. doi:10.1038/20670.
- Zhou, Z.; Wang, X. (2000). "A new species of Caudipteryx from the Yixian Formation of Liaoning, northeast China" (PDF). Vertebrata Palasiatica 38 (2): 113–130.
- Zhou, Z.; Wang, X.; Zhang, F.; Xu, X. (2000). "Important features of Caudipteryx - Evidence from two nearly complete new specimens" (PDF). Vertebrata Palasiatica 38 (4): 241–254.
- Xu, Xing; Zhou, Zhonghe; Wang, Xiaolin (2000). "The smallest known non-avian theropod dinosaur" (PDF). Nature 408 (6813): 705–708. doi:10.1038/35047056. PMID 11130069.
- Barsbold R., Osmólska H., Watabe M., Currie P.J., Tsogtbaatar K. (2000). "New Oviraptorosaur (Dinosauria, Theropoda) From Mongolia: The First Dinosaur With A Pygostyle" (PDF). Acta Palaeontologica Polonica 45 (2): 97–106.
- Mayr, Gerald; Peters, Stefan; Plodowski, Gerhard; Vogel, Olaf (2002). "Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus". Naturwissenschaften 89 (8): 361–365. Bibcode:2002NW.....89..361M. doi:10.1007/s00114-002-0339-6. PMID 12435037.
- Xu X., Wang X.-L. (2003). "A new maniraptoran from the Early Cretaceous Yixian Formation of western Liaoning". Vertebrata PalAsiatica 41 (3): 195–202.
- Xu, X., Norell, M. A., Kuang, X., Wang, X., Zhao, Q., Jia, C. (2004). "Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids". Nature 431 (7009): 680–684. Bibcode:2004Natur.431..680X. doi:10.1038/nature02855. PMID 15470426.
- Ji Q., Ji S., Lu J., You H., Chen W., Liu Y., Liu Y. (2005). "First avialan bird from China (Jinfengopteryx elegans gen. et sp. nov.)". Geological Bulletin of China 24 (3): 197–205.
- Turner, Alan H.; Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; and Norell, Mark (2007). "A basal dromaeosaurid and size evolution preceding avian flight" (pdf). Science 317 (5843): 1378–1381. Bibcode:2007Sci...317.1378T. doi:10.1126/science.1144066. PMID 17823350.
- Goehlich U.B., Tischlinger H., Chiappe L.M. (2006). "Juraventaor starki (Reptilia, Theropoda) ein nuer Raubdinosaurier aus dem Oberjura der Suedlichen Frankenalb (Sueddeutschland): Skelettanatomie und Wiechteilbefunde". Archaeopteryx 24: 1–26.
- Chiappe, Luis M.; Göhlich, Ursula B. (2010). "Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 258 (3): 257–296. doi:10.1127/0077-7749/2010/0125.
- Ji S., Ji Q., Lu J., Yuan C. (2007). "A new giant compsognathid dinosaur with long filamentous integuments from Lower Cretaceous of Northeastern China". Acta Geologica Sinica 81 (1): 8–15.
- 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.
- Xu, Xing; Zheng, Xiaoting; You, Hailu (2010). "Exceptional dinosaur fossils show ontogenetic development of early feathers". Nature 464 (7293): 1338–1341. Bibcode:2010Natur.464.1338X. doi:10.1038/nature08965. PMID 20428169.
- Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures". Nature 458 (7236): 333–336. Bibcode:2009Natur.458..333Z. doi:10.1038/nature07856. PMID 19295609.
- Xu, Xing; Wang, Kebai; Zhang, Ke; Ma, Qingyu; Xing, Lida; Sullivan, Corwin; Hu, Dongyu; Cheng, Shuqing et al. (2012). "A gigantic feathered dinosaur from the Lower Cretaceous of China". Nature 484 (7392): 92–95. Bibcode:2012Natur.484...92X. doi:10.1038/nature10906. PMID 22481363.
- En-Pu Gong, Larry D. Martin, David A. Burnham, Amanda R. Falk and Lian-Hai Hou (2012). "A new species of Microraptor from the Jehol Biota of northeastern China". Palaeoworld. in press (2): 81. doi:10.1016/j.palwor.2012.05.003.
- Rauhut, O. W. M.; Foth, C.; Tischlinger, H.; Norell, M. A. (2012). "Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany". Proceedings of the National Academy of Sciences 109 (29): 11746–11751. doi:10.1073/pnas.1203238109. PMC 3406838. PMID 22753486.
- Darla K. Zelenitsky, François Therrien, Gregory M. Erickson, Christopher L. DeBuhr, Yoshitsugu Kobayashi, David A. Eberth and Frank Hadfield (2012). "Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins". Science 338 (6106): 510–514. Bibcode:2012Sci...338..510Z. doi:10.1126/science.1225376. PMID 23112330.
- Ji Qiang, Lü Jun-Chang, Wei Xue-Fang, Wang Xu-Ri (2012). "A new oviraptorosaur from the Yixian Formation of Jianchang, Western Liaoning Province, China". Regional Geology of China (12): 2102–2107.
- Hanyong Pu, Yoshitsugu Kobayashi, Junchang Lü, Li Xu, Yanhua Wu, Huali Chang, Jiming Zhang, Songhai Jia (2013). "An unusual basal therizinosaur dinosaur with an ornithischian dental arrangement from northeastern China". PLoS ONE 8 (5): Article number e63423. Bibcode:2013PLoSO...863423P. doi:10.1371/journal.pone.0063423.
- W. Scott Persons, IV, Philip J. Currie, and Mark A. Norell (2013). "Oviraptorosaur tail forms and functions". Acta Palaeontologica Polonica. doi:10.4202/app.2012.0093.
- Gang Han, Luis M. Chiappe,Shu-An Ji, Michael Habib, Alan H. Turner, Anusuya Chinsamy, Xueling Liu, Lizhuo Han (2014). "A new raptorial dinosaur with exceptionally long feathering provides insights into dromaeosaurid flight performance". Nature Communications 5: Article number 4382. doi:10.1038/ncomms5382.
- Pascal Godefroit, Sofia M. Sinitsa, Danielle Dhouailly, Yuri L. Bolotsky, Alexander V. Sizov, Maria E. McNamara, Michael J. Benton, Paul Spagna (2014). "A Jurassic ornithischian dinosaur from Siberia with both feathers and scales". Science 25 (345): 451–455. doi:10.1126/science.1253351.
- 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. ISBN 1-932075-01-1.
- Prum, R. & Brush A.H. (2002). "The evolutionary origin and diversification of feathers". The Quarterly Review of Biology 77 (3): 261–295. doi:10.1086/341993. PMID 12365352.
- Prum, R (1999). "Development and evolutionary origin of feathers". Journal of Experimental Zoology 285 (4): 291–306. doi:10.1002/(SICI)1097-010X(19991215)285:4<291::AID-JEZ1>3.0.CO;2-9. PMID 10578107.
- Norell, M. Xu, X. (2005) "The Varieties of Tyrannosaurs" Natural History Magazine May 2005.
- Dimond, C. C.,R. J. Cabin and J. S. Brooks (2011). "Feathers, Dinosaurs, and Behavioral Cues: Defining the Visual Display Hypothesis for the Adaptive Function of Feathers in Non-Avian Theropods". BIOS 82 (3): 58–63. doi:10.1893/011.082.0302.
- Sumida, S. S. and C. A. Brochu (2000). "Phylogenetic Context for the Origin of Feathers". American Zoologist 40 (4): 485–503. doi:10.1093/icb/40.4.486.
- Lingham-Soliar, T. (2011). "The evolution of the feather: Sinosauropteryx, a colourful tail". Journal of Ornithology 152 (3): 567–577. doi:10.1007/s10336-010-0620-y.
- Vinther, J., D. E. G. Briggs, R. O. Prum and V. Saranathan (2008). "The colour of fossil feathers". Biology Letters 4 (5): 522–525. doi:10.1098/rsbl.2008.0302. PMC 2610093. PMID 18611841.
- Zhang, F. C., S. L. Kearns, P. J. Orr, M. J. Benton, Z. H. Zhou, D. Johnson, X. Xu X. L. Wang (2010). "Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds". Nature 463 (7284): 1075–1078. Bibcode:2010Natur.463.1075Z. doi:10.1038/nature08740. PMID 20107440.
- Li, Q. G.,K. Q. Gao,Q. J. Meng,M. D. Shawkey,L. D'Alba,R. Pei,M. Ellison,M. A. Norell and J. Vinther (2012). "Reconstruction of Microraptor and the Evolution of Iridescent Plumage". Science 335 (6073): 1215–1219. Bibcode:2012Sci...335.1215L. doi:10.1126/science.1213780. PMID 22403389.
- Stevens, K.A. (20006). Journal of Vertebrate Paleontology 26. pp. 11746–11751.
- Gould, Stephen J. and Vrba, Elisabeth S. (1982). "Exaptation: a missing term in the science of form". Paleobiology 8 (1): 4–15.
- Reichholf, J. H. (1996). "Die Feder, die Mauser und der Urspring der Vögel. Ein neure Sicht zur Evolution der Vögel". Archaeopteryx 1427 (38).
- Bock, W. J. (2000). "Explanatory History of the Origin of Feathers". Amer. Zool. 40 (4): 478–485. doi:10.1093/icb/40.4.478.
- Xu, X.; Zheng, X.; You, H. (2009). "A new feather type in a nonavian theropod and the early evolution of feathers". Proceedings of the National Academy of Sciences 106 (3): 832–4. Bibcode:2009PNAS..106..832X. doi:10.1073/pnas.0810055106. PMC 2630069. PMID 19139401.
- Zhang, Fucheng; Zhou, Zhonghe; Xu, Xing; Wang, Xiaolin; Sullivan, Corwin (2008). "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers". Nature 455 (7216): 1105–8. Bibcode:2008Natur.455.1105Z. doi:10.1038/nature07447. PMID 18948955.
- Zelenitsky, D. K.; Therrien, F.; Erickson, G. M.; Debuhr, C. L.; Kobayashi, Y.; Eberth, D. A.; Hadfield, F. (2012). "Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins". Science 338 (6106): 510–514. doi:10.1126/science.1225376. PMID 23112330.
- 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. PMID 23719374.
- DinoBuzz, dinosaur-bird controversy explained, by UC Berkeley.