Editing Feather (section)

==Evolution==
{{Main|Origin of avian flight}}
{{multiple image
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 | image1    = Archaeopteryx (Feather).jpg
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 | caption1  = [[Late Jurassic]] fossil feather of an unidentified dinosaur, once thought to be ''[[Archaeopteryx]]''.<!--although this feather was given the name 'Archaeopteryx', in turns out to be non-avian. See Archaeopteryx article.-->
 | image2    = Rachis-dominated feathers Burmese amber NMNS.jpg
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 | caption2  = Rachis-dominated feathers inside mid-[[Cretaceous]] [[Burmese amber]]
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=== Functional considerations ===
The functional view on the evolution of feathers has traditionally focused on insulation, flight and display. Discoveries of non-flying Late Cretaceous feathered dinosaurs in China,<ref name="NYT-20161208">{{cite news |last=St. Fleur |first=Nicholas |title=That Thing With Feathers Trapped in Amber? It Was a Dinosaur Tail |url=https://www.nytimes.com/2016/12/08/science/dinosaur-feathers-amber.html |date=8 December 2016 |work=[[The New York Times]] |access-date=8 December 2016 |url-status=live |archive-url=https://web.archive.org/web/20161208224540/http://www.nytimes.com/2016/12/08/science/dinosaur-feathers-amber.html |archive-date=8 December 2016 }}</ref> however, suggest that flight could not have been the original primary function as the feathers simply would not have been capable of providing any form of lift.<ref name="sumida">{{Cite journal|author1=Sumida, SS|author2=CA Brochu|year=2000|title=Phylogenetic context for the origin of feathers|doi=10.1093/icb/40.4.486|journal=American Zoologist|volume=40|issue=4|pages=486–503|doi-access=free}}</ref><ref>{{Cite journal|author1=Dimond, C. C. |author2=R. J. Cabin |author3=J. S. Brooks |journal=BIOS|title=Feathers, Dinosaurs, and Behavioral Cues: Defining the Visual Display Hypothesis for the Adaptive Function of Feathers in Non-Avian Theropods | volume=82|year=2011|pages=58–63 | doi=10.1893/011.082.0302|issue=3|s2cid=98221211}}</ref> There have been suggestions that feathers may have had their original function in thermoregulation, waterproofing, or even as sinks for metabolic wastes such as sulphur.<ref>{{cite journal| title= Explanatory History of the Origin of Feathers|author=Bock, WJ|year=2000| journal= Am. Zool.|volume=40 |issue=4|pages=478–485 |doi=10.1093/icb/40.4.478|doi-access=free}}</ref> [[Yutyrannus|Recent discoveries]] are argued to support a thermoregulatory function, at least in smaller dinosaurs.<ref>{{Cite journal |date=4 April 2012 |author=Whitfield, John |title=Largest feathered dinosaur yet discovered in China |journal=Nature News Blog |url=http://blogs.nature.com/news/2012/04/largest-feathered-dinosaur-discovered-in-china.html |access-date=4 April 2012 |url-status=live |archive-url=https://web.archive.org/web/20120406145618/http://blogs.nature.com/news/2012/04/largest-feathered-dinosaur-discovered-in-china.html |archive-date=6 April 2012 }}</ref><ref name="yutyrannus">{{cite journal |author1=Xu X. |author2=Wang K. |author3=Zhang K. |author4=Ma Q. |author5=Xing L. |author6=Sullivan C. |author7=Hu D. |author8=Cheng S. |author9=Wang S. |year=2012 |title=A gigantic feathered dinosaur from the Lower Cretaceous of China |url=http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf |journal=Nature |volume=484 |issue=7392 |pages=92–95 |doi=10.1038/nature10906 |pmid=22481363 |bibcode=2012Natur.484...92X |s2cid=29689629 |display-authors=etal |archive-url=https://web.archive.org/web/20120417134949/http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf |archive-date=17 April 2012 }}</ref> Some researchers even argue that thermoregulation arose from bristles on the face that were used as tactile sensors.<ref>{{Cite journal|last1=Persons|first1=Walter S.|last2=Currie|first2=Philip J.|date=2015|title=Bristles before down: A new perspective on the functional origin of feathers|journal=Evolution|language=en|volume=69|issue=4|pages=857–862|doi=10.1111/evo.12634|issn=1558-5646|pmid=25756292|s2cid=24319963|doi-access=free}}</ref> While feathers have been suggested as having evolved from reptilian [[scale (zoology)|scales]], there are numerous objections to that idea, and more recent explanations have arisen from the paradigm of [[evolutionary developmental biology]].<ref name="Prum2003" /> Theories of the scale-based origins of feathers suggest that the planar scale structure was modified for development into feathers by splitting to form the webbing; however, that developmental process involves a tubular structure arising from a follicle and the tube splitting longitudinally to form the webbing.<ref name="Prum2002" /><ref name="Prum2003" /> The number of feathers per unit area of skin is higher in smaller birds than in larger birds, and this trend points to their important role in thermal insulation, since smaller birds lose more heat due to the relatively larger surface area in proportion to their body weight.<ref name="pettingill" /> The miniaturization of birds also played a role in the evolution of powered flight.<ref>{{Cite journal|author1=De Ricqles |author2=A. J. |author3=K. Padian |author4=J. R. Horner |author5=E. T. Lamm |author6=N. Myhrvold |year=2003|title=Osteohistology of confuciusornis sanctus (theropoda: Aves)|journal=Journal of Vertebrate Paleontology|volume=23|issue=2 |pages=373–386|doi=10.1671/0272-4634(2003)023[0373:oocsta]2.0.co;2 |s2cid=84936431 }}</ref> The coloration of feathers is believed to have evolved primarily in response to [[sexual selection]]. In fossil specimens of the [[Paraves|paravian]] ''[[Anchiornis huxleyi]]'' and the [[pterosaur]] ''[[Tupandactylus imperator]]'', the features are so well preserved that the [[melanosome]] (pigment cells) structure can be observed. By comparing the shape of the fossil melanosomes to melanosomes from extant birds, the color and pattern of the feathers on ''Anchiornis'' and ''Tupandactylus'' could be determined.<ref>{{cite journal|last1=Li|first1=Quanguo|last2=Gao|first2=Ke-Qin|last3=Vinther|first3=Jakob|last4=Shawkey|first4=Matthew|last5=Clarke|first5=Julia|last6=D'Alba|first6=Liliana|last7=Meng|first7=Qingjin|last8=Briggs|first8=Derek|last9=Prum|first9=Richard|title=Plumage Color Patterns of an Extinct Dinosaur|journal=Science|date=12 March 2010|volume=327|issue=5971|pages=1369–1372|doi=10.1126/science.1186290|pmid=20133521|bibcode = 2010Sci...327.1369L |s2cid=206525132|url=http://doc.rero.ch/record/210394/files/PAL_E4402.pdf}}</ref><ref>Cincotta, A., Nicolaï, M., Campos, H.B.N. et al. Pterosaur melanosomes support signalling functions for early feathers. Nature 604, 684–688 (2022). {{doi|10.1038/s41586-022-04622-3}}.</ref> ''Anchiornis'' was found to have black-and-white-patterned feathers on the forelimbs and hindlimbs, with a reddish-brown crest. This pattern is similar to the coloration of many extant bird species, which use plumage coloration for display and communication, including sexual selection and camouflage. It is likely that non-avian dinosaur species utilized plumage patterns for similar functions as modern birds before the origin of flight. In many cases, the physiological condition of the birds (especially males) is indicated by the quality of their feathers, and this is used (by the females) in [[mate choice]].<ref>{{Cite journal|author1=Saino, Nicola |author2=Riccardo Stradi|s2cid=4400888|year=1999|title=Carotenoid Plasma Concentration, Immune Profile, and Plumage Ornamentation of Male Barn Swallows|journal=American Naturalist|volume=154|issue=4|pages=441–448|doi=10.1086/303246|pmid=10523490}}</ref><ref>{{Cite journal|author1=Endler, John A. |author2=David A. Westcott |author3= Joah R. Madden |author4=Tim Robson |author5= Patrick Phillips  |name-list-style=amp |year=2005|title=Animal visual systems and the evolution of color patterns: Sensory processing illumiates signal evolution|journal=Evolution|volume=59|issue=8|pages=1795–1818|pmid=16329248|doi=10.1111/j.0014-3820.2005.tb01827.x|s2cid=25683790 |doi-access=free}}</ref> Additionally, when comparing different ''[[Ornithomimus|Ornithomimus edmontonicus]]'' specimens, older individuals were found to have a pennibrachium (a wing-like structure consisting of elongate feathers), while younger ones did not. This suggests that the pennibrachium was a secondary sex characteristic and likely had a sexual function.<ref>{{Cite journal|last1=Zelenitsky|first1=D. K.|last2=Therrien|first2=F.|last3=Erickson|first3=G. M.|last4=DeBuhr|first4=C. L.|last5=Kobayashi|first5=Y.|last6=Eberth|first6=D. A.|last7=Hadfield|first7=F.|date=2012-10-26|title=Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins|journal=Science|language=en|volume=338|issue=6106|pages=510–514|doi=10.1126/science.1225376|pmid=23112330|issn=0036-8075|bibcode=2012Sci...338..510Z|s2cid=2057698}}</ref>

=== Molecular evolution ===
Several [[gene]]s have been found to determine feather development. They will be key to understand the evolution of feathers. For instance, some genes convert scales into feathers or feather-like structures when expressed or induced in bird feet, such as the scale-feather converters [[SOX2|Sox2]], [[ZIC1|Zic1]], [[Gremlin (protein)|Grem1]], [[SPRY2|Spry2]], and [[SOX18|Sox18]].<ref>{{Cite journal|last1=Wu|first1=Ping|last2=Yan|first2=Jie|last3=Lai|first3=Yung-Chih|last4=Ng|first4=Chen Siang|last5=Li|first5=Ang|last6=Jiang|first6=Xueyuan|last7=Elsey|first7=Ruth M.|last8=Widelitz|first8=Randall|last9=Bajpai|first9=Ruchi|last10=Li|first10=Wen-Hsiung|last11=Chuong|first11=Cheng-Ming|date=2018-02-01|title=Multiple Regulatory Modules Are Required for Scale-to-Feather Conversion|journal=Molecular Biology and Evolution|volume=35|issue=2|pages=417–430|doi=10.1093/molbev/msx295|issn=1537-1719|pmc=5850302|pmid=29177513}}</ref>

Feathers and scales are made up of two distinct forms of [[keratin]], and it was long thought that each type of keratin was exclusive to each skin structure (feathers and scales). However, feather keratin is also present in the early stages of development of [[American alligator]] scales. This type of keratin, previously thought to be specific to feathers, is suppressed during embryological development of the alligator and so is not present in the scales of mature alligators. The presence of this [[Homology (biology)|homologous]] keratin in both birds and [[crocodilian]]s indicates that it was inherited from a common ancestor.<ref>{{Cite journal |last1=Alibardi |first1=L. |last2=Knapp |first2=L. W. |last3=Sawyer |first3=R. H. |date=June 2006 |title=Beta-keratin localization in developing alligator scales and feathers in relation to the development and evolution of feathers |url=https://www.researchgate.net/publication/6055177 |journal=Journal of Submicroscopic Cytology and Pathology |volume=38 |issue=2–3 |pages=175–192 |issn=1122-9497 |pmid=17784647}}</ref>

This may suggest that crocodilian scales, bird and dinosaur feathers, and pterosaur [[pycnofibre]]s are all developmental expressions of the same primitive archosaur skin structures; suggesting that feathers and pycnofibers could be homologous.<ref>{{cite journal |last1=Alibardi |first1=L |last2=Knapp |first2=LW |last3=Sawyer |first3=RH |year=2006 |title=Beta-keratin localization in developing alligator scales and feathers in relation to the development and evolution of feathers |url=https://www.researchgate.net/publication/6055177 |journal=Journal of Submicroscopic Cytology and Pathology |volume=38 |issue=2–3 |pages=175–92 |pmid=17784647}}</ref> Molecular dating methods in 2011 show that the subfamily of feather β-keratins found in extant birds started to diverge 143 million years ago, suggesting the pennaceous feathers of ''Anchiornis'' were not made of the feather β-keratins present in extant birds.<ref>{{Cite journal |last1=Greenwold |first1=Matthew J. |last2=Sawyer |first2=Roger H. |date=2011-12-15 |title=Linking the molecular evolution of avian beta (β) keratins to the evolution of feathers |url=https://d1wqtxts1xzle7.cloudfront.net/50801629/jez.b.2143620161209-26901-9mlb8t-with-cover-page-v2.pdf?Expires=1665801383&Signature=gJjg-n6ADk7cVZ2dpCUno4Q8X~l2ixG6T8NxcOwJxsDy1RgCxwvNv2UpiHylOeKMuq2TBU~~W0gxtieZHVMOjC1bQONwqdlg0xcNkKIvNXoGxrr7tRZ5J2DfxrJ-3JsT~Uns8SZ1ry8wBbv5V0Hz1etiFG4nPqs5Yx4b0D9xS2vVr~wIcqed8x84xspBlysJjavqztbFOLKPfGN7x9ez~L4sno3CogZU9bVpqD6Zq~w53esghZrWV5VQCw25je43qNFiWixHAi~aeFRpLP0IiiTFJc64XpHEiAMlu4Buh4ypOdP1z7Imnnc-bj3opJ1FSbM3VizRyqxdvDrNOMsEMw__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=Journal of Experimental Zoology Part B: Molecular and Developmental Evolution |language=en |volume=316B |issue=8 |pages=609–616 |doi=10.1002/jez.b.21436 |pmid=21898788 |bibcode=2011JEZB..316..609G |access-date=15 October 2022 |archive-date=15 October 2022 |archive-url=https://web.archive.org/web/20221015014225/https://d1wqtxts1xzle7.cloudfront.net/50801629/jez.b.2143620161209-26901-9mlb8t-with-cover-page-v2.pdf?Expires=1665801383&Signature=gJjg-n6ADk7cVZ2dpCUno4Q8X~l2ixG6T8NxcOwJxsDy1RgCxwvNv2UpiHylOeKMuq2TBU~~W0gxtieZHVMOjC1bQONwqdlg0xcNkKIvNXoGxrr7tRZ5J2DfxrJ-3JsT~Uns8SZ1ry8wBbv5V0Hz1etiFG4nPqs5Yx4b0D9xS2vVr~wIcqed8x84xspBlysJjavqztbFOLKPfGN7x9ez~L4sno3CogZU9bVpqD6Zq~w53esghZrWV5VQCw25je43qNFiWixHAi~aeFRpLP0IiiTFJc64XpHEiAMlu4Buh4ypOdP1z7Imnnc-bj3opJ1FSbM3VizRyqxdvDrNOMsEMw__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |url-status=dead }}</ref> However, a study of fossil feathers from the dinosaur Sinosauropteryx and other fossils revealed traces of beta-sheet proteins, using infrared spectroscopy and sulfur-X-ray spectroscopy. The presence of abundant alpha-proteins in some fossil feathers was shown to be an artefact of the fossilization process, as beta-protein structures are readily altered to alpha-helices during thermal degradation.<ref>{{cite journal |last1=Slater |first1=Tiffany S |last2=Edwards |first2=Nicholas P |last3=Webb |first3=Samuel M |last4=Zhang |first4=Fucheng |last5=McNamara |first5=Maria E |title=Preservation of corneous β-proteins in Mesozoic feathers |journal=Nature Ecology & Evolution |date=2023 |volume=7 |issue=10 |pages=1706–1713 |doi=10.1038/s41559-023-02177-8 |pmid=37735563 |bibcode=2023NatEE...7.1706S |osti=2327098 |s2cid=262125827 |url=https://www.nature.com/articles/s41559-023-02177-8}}</ref> In 2019, scientists found that genes for the production of feathers evolved at the base of archosauria, supporting that feathers were present at early ornithodirans and is consistent with the fossil record.<ref name=":0">{{Cite journal |last1=Benton |first1=Michael J. |last2=Dhouailly |first2=Danielle |last3=Jiang |first3=Baoyu |last4=McNamara |first4=Maria |date=2019-09-01 |title=The Early Origin of Feathers |url=https://cora.ucc.ie/bitstream/handle/10468/8068/10285.pdf?sequence=1 |journal=Trends in Ecology & Evolution |language=en |volume=34 |issue=9 |pages=856–869 |doi=10.1016/j.tree.2019.04.018 |pmid=31164250 |bibcode=2019TEcoE..34..856B |hdl=10468/8068 |s2cid=174811556 |issn=0169-5347}}</ref>

===Feathered dinosaurs===
{{Main|Feathered dinosaurs}}
[[File:Archaeopteryx lithographica (Berlin specimen).jpg|thumb|left|upright|''[[Archaeopteryx lithographica]]'' (Berlin specimen)]]
Several non-avian [[feathered dinosaurs|dinosaurs]] had feathers on their limbs that would not have functioned for flight.<ref name="NYT-20161208" /><ref name=Prum2003/> One theory suggests that feathers originally evolved on dinosaurs due to their [[Thermal insulation|insulation]] properties; then, small dinosaur species which grew longer feathers may have found them helpful in gliding, leading to the evolution of proto-birds like ''[[Archaeopteryx]]'' and ''[[Microraptor]] zhaoianus''. Another theory posits that the original adaptive advantage of early feathers was their pigmentation or iridescence, contributing to sexual preference in mate selection.<ref>
{{Cite journal|author1=Dimond, C. C. |author2=R. J. Cabin |author3=J. S. Brooks |journal=BIOS
|title=Feathers, Dinosaurs, and Behavioral Cues: Defining the Visual Display Hypothesis for the Adaptive Function of Feathers in Non-Avian Theropods|volume=82|year=2011|pages=58–63|doi=10.1893/011.082.0302|issue=3|s2cid=98221211
}}
</ref> Dinosaurs that had feathers or protofeathers include ''[[Pedopenna]] daohugouensis''<ref>
{{Cite journal|journal= Naturwissenschaften|title=A new maniraptoran dinosaur from China with long feathers on the metatarsus|volume=92|issue=4|pages=173–177|author1=Xu, Xing  |author2=Fucheng Zhang|doi=10.1007/s00114-004-0604-y|year= 2005|pmid= 15685441|bibcode=2005NW.....92..173X|s2cid=789908}}
</ref> and ''[[Dilong paradoxus]]'', a [[tyrannosauroid]] which is 60 to 70 million years older than ''[[Tyrannosaurus|Tyrannosaurus rex]].''<ref>
{{Cite journal|author=Xu, Xing|s2cid=1516713|title=Feathered dinosaurs from China and the evolution of major avian characters|journal=Integrative Zoology|volume=1|issue=1|pages=4–11|year=2006|doi=10.1111/j.1749-4877.2006.00004.x|pmid=21395983|doi-access=free}}</ref>

The majority of dinosaurs known to have had feathers or protofeathers are [[Theropoda|theropods]], however featherlike "filamentous integumentary structures" are also known from the [[ornithischian]] dinosaurs ''[[Tianyulong]]'' and ''[[Psittacosaurus]]''.<ref>{{Cite journal|author1=Zheng, X. T. |author2=H. L. You |author3= X. Xu |author4= Z. M. Dong |name-list-style=amp |journal=Nature|title=An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures|volume=458|year=2009|pages=333–336|doi=10.1038/nature07856|pmid=19295609|issue=7236|bibcode = 2009Natur.458..333Z |s2cid=4423110 }}</ref> The exact nature of these structures is still under study. However, it is believed that the stage-1 feathers (see [[Feather#Evolutionary stages|Evolutionary stages]] section below) such as those seen in these two ornithischians likely functioned in display.<ref name="xu&guo2009"/> In 2014, the ornithischian ''[[Kulindadromeus]]'' was reported as having structures resembling stage-3 feathers.<ref name="Godefroit2014" /> The likelihood of scales evolving on early dinosaur ancestors are high. However, this was by assuming that primitive pterosaurs were scaly.<ref>{{Cite journal|last1=Barrett|first1=Paul M.|last2=Evans|first2=David C.|last3=Campione|first3=Nicolás E.|date=2015-06-30|title=Evolution of dinosaur epidermal structures|journal=Biology Letters|volume=11|issue=6|page=20150229|doi=10.1098/rsbl.2015.0229|pmc=4528472|pmid=26041865}}</ref><ref name="youtube.com">{{Citation|title=Those feathers won't stick: maximum likelihood modelling supports scales as primitive for Dinosauria (The 66th Symposium on Vertebrate Palaeontology and Comparative Anatomy)|url=https://www.youtube.com/watch?v=2MOCbXPwshA| archive-url=https://ghostarchive.org/varchive/youtube/20211211/2MOCbXPwshA| archive-date=2021-12-11 | url-status=live|publication-date=November 9, 2018|language=en|access-date=2021-10-03}}{{cbignore}}</ref> A 2016 study analyzes the pulp morphology of the tail bristles of ''Psittacosaurus'' and finds they are similar to feathers but notes that they are also similar to the bristles on the head of the [[Congo peafowl]], the beard of the [[Turkey (bird)|turkey]], and the spine on the head of the [[horned screamer]].<ref>{{Cite journal |last1=Mayr |first1=Gerald |last2=Pittman |first2=Michael |last3=Saitta |first3=Evan |last4=Kaye |first4=Thomas G. |last5=Vinther |first5=Jakob |date=August 30, 2016 |editor-last=Benson |editor-first=Roger |title=Structure and homology of Psittacosaurus tail bristles |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12257 |journal=Palaeontology |language=en |volume=59 |issue=6 |pages=793–802 |doi=10.1111/pala.12257|bibcode=2016Palgy..59..793M |hdl=1983/029c668f-08b9-45f6-a0c5-30ce9256e593 |s2cid=89156313 |hdl-access=free }}</ref> A reestimation of maximum likelihoods by paleontologist [[Thomas R. Holtz Jr.|Thomas Holtz]] finds that filaments were more likely to be the ancestral state of dinosaurs.<ref>{{Cite web |last=Holtz |first=Thomas |date=2018-10-19 |title="Integumentary Status: It's Complicated': Phylogenetic, Sedimentary, and Biological Impediments to Resolving the Ancestral Integument of Mesozoic Dinosauria |url=https://vertpaleo.org/wp-content/uploads/2021/03/SVP-2018-program-book-V4-FINAL-with-covers-9-24-18.pdf |access-date=2022-07-16 |website=Society of Vertebrate Paleontology |language=en-US}}</ref>

In 2010, a [[Carcharodontosauridae|carcharodontosaurid]] named [[Concavenator|''Concavenator corcovatus'']] was found to have [[Flight feather#Remiges|remiges]] on the ulna suggesting it might have had quill-like structures on the ams.<ref>{{Cite journal|last1=Ortega|first1=Francisco|last2=Escaso|first2=Fernando|last3=Sanz|first3=José L.|date=September 9, 2010|title=A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain|url=https://www.nature.com/articles/nature09181|journal=Nature|language=en|volume=467|issue=7312|pages=203–206|doi=10.1038/nature09181|pmid=20829793|bibcode=2010Natur.467..203O|s2cid=4395795|issn=1476-4687}}</ref> However, Foth et al. 2014 disagress with the publication where they point out that the bumps on the ulna of ''Concavenator'' are on the [[Anatomical terms of location#Main terms|anterolateral]] which is unlike remiges which are in a [[Anatomical terms of location#Main terms|posterolateral]] on the ulna of some birds, they consider it more likely that these are attachments for interosseous ligaments.<ref>{{Cite journal|last1=Foth|first1=Christian|last2=Tischlinger|first2=Helmut|last3=Rauhut|first3=Oliver W.M.|date=2014-06-02|title=New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers|url=https://www.nature.com/articles/nature13467|journal=Nature|volume=511|issue=7507|pages=79–82|doi=10.1038/nature13467|pmid=24990749|bibcode=2014Natur.511...79F|s2cid=4464659}}</ref> This was refuted by Cuesta Fidalgo and her colleagues, they pointed out that these bumps on the ulna are posterolateral which is unlike that of interosseous ligaments.<ref>{{Cite journal |last1=Cuesta |first1=Elena |last2=Ortega |first2=Francisco |last3=Sanz |first3=José Luis |date=2018-07-04 |title=Appendicular osteology of Concavenator corcovatus (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of Spain |journal=Journal of Vertebrate Paleontology |volume=38 |issue=4 |pages=(1)–(24) |doi=10.1080/02724634.2018.1485153 |s2cid=91976402 |issn=0272-4634|url=https://figshare.com/articles/journal_contribution/7177802 }}</ref>

Since the 1990s, dozens of feathered dinosaurs have been discovered in the clade [[Maniraptora]], which includes the clade Avialae and the recent common ancestors of birds, [[Oviraptorosauria]] and [[Deinonychosauria]]. In 1998, the discovery of a feathered oviraptorosaurian, ''Caudipteryx zoui'', challenged the notion of feathers as a structure exclusive to Avialae.<ref>{{Cite journal|doi=10.1038/31635 |author=Ji, Q. |author2=P. J. Currie |author3=M. A. Norell |author4=S. A. Ji
|title=Two feathered dinosaurs from northeastern China |journal=Nature |volume=393 |year=1998 |pages=753–761
|issue=6687|bibcode = 1998Natur.393..753Q |s2cid=205001388
|url=http://doc.rero.ch/record/31829/files/PAL_E1436.pdf
}}
</ref> Buried in the Yixian Formation in Liaoning, China, ''C. zoui'' lived during the Early Cretaceous Period. Present on the forelimbs and tails, their integumentary structure has been accepted{{by whom|date=April 2014}} as pennaceous vaned feathers based on the rachis and herringbone pattern of the barbs. In the clade Deinonychosauria, the continued divergence of feathers is also apparent in the families [[Troodontidae]] and [[Dromaeosauridae]]. Branched feathers with rachis, barbs, and barbules were discovered in many members including ''Sinornithosaurus millenii'', a dromaeosaurid found in the Yixian formation (124.6 MYA).<ref>
{{Cite journal|doi=10.1038/35065589 |author1=Xu, X. |author2=H. H. Zhou |author3= R. O. Prum  |name-list-style=amp |title=Branched integumental structures in Sinornithosaurus and the origin of feathers |journal=Nature |volume=410
|issue=6825 |year=2001 |pages=200–204 |pmid=11242078 |bibcode=2001Natur.410..200X |s2cid=4426803 }}</ref>

Previously, a temporal paradox existed in the evolution of feathers—theropods with highly derived bird-like characteristics occurred at a later time than ''[[Archaeopteryx]]''—suggesting that the descendants of birds arose before the ancestor. However, the discovery of ''Anchiornis huxleyi'' in the Late Jurassic Tiaojishan Formation (160 MYA) in western Liaoning in 2009<ref>
{{Cite journal |author=Hu, D. Y. |author2=L. H. Hou |author3=L. J. Zhang |author4=X. Xu
|title=A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus |journal=Nature
|volume=461 |issue=7264 |year=2009 |pages=640–643 |pmid=19794491 |doi=10.1038/nature08322
|bibcode=2009Natur.461..640H|s2cid=205218015 }}
</ref><ref>
{{Cite journal|author1=Xu, X. |author2=Q. Zhao |author3= M. Norell |author4=C. Sullivan |author5= D. Hone |author6=G. Erickson |author7= X. L. Wang |title=A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin
|journal=Chinese Science Bulletin |volume=54 |year=2009 |pages=430–435 |doi=10.1007/s11434-009-0009-6|issue=3|bibcode=2009SciBu..54..430X |display-authors=etal|doi-access=free }}
</ref>
resolved this paradox. By predating ''Archaeopteryx'', ''Anchiornis'' proves the existence of a modernly feathered theropod ancestor, providing insight into the dinosaur-bird transition. The specimen shows distribution of large pennaceous feathers on the forelimbs and tail, implying that pennaceous feathers spread to the rest of the body at an earlier stage in theropod evolution.<ref>
{{Cite journal|author=Witmer, L. M. |title=Feathered dinosaurs in a tangle |journal=Nature |volume=461 |issue=7264
|year=2009 |pages=601–602 |pmid=19794481 |doi=10.1038/461601a|bibcode = 2009Natur.461..601W |s2cid=205049989 |doi-access=free }}
</ref> The development of pennaceous feathers did not replace earlier filamentous feathers. Filamentous feathers are preserved alongside modern-looking flight feathers – including some with modifications found in the feathers of extant diving birds – in 80 million year old amber from Alberta.<ref>
{{cite news | url=https://www.cbc.ca/news/science/dinosaur-feathers-found-in-alberta-amber-1.1086765 | work=CBC News | title=Dinosaur feathers found in Alberta amber | date=15 September 2011 | url-status=live | archive-url=https://web.archive.org/web/20110915200138/http://www.cbc.ca/news/canada/edmonton/story/2011/09/15/science-dinosaur-feathers.html | archive-date=15 September 2011 }}
</ref>

Two small wings trapped in amber dating to 100 mya show [[plumage]] existed in some bird predecessors. The wings most probably belonged to [[enantiornithes]], a diverse group of avian dinosaurs.<ref>{{Cite web|url=http://news.nationalgeographic.com/2016/06/dinosaur-bird-feather-burma-amber-myanmar-flying-paleontology-enantiornithes|title=Rare Dinosaur-Era Bird Wings Found Trapped in Amber|date=2016-06-28|access-date=2016-06-28|url-status=dead|archive-url=https://web.archive.org/web/20160628165734/http://news.nationalgeographic.com/2016/06/dinosaur-bird-feather-burma-amber-myanmar-flying-paleontology-enantiornithes/|archive-date=28 June 2016}}</ref><ref>{{Cite journal|last1=Xing|first1=Lida|last2=McKellar|first2=Ryan C.|last3=Wang|first3=Min|last4=Bai|first4=Ming|last5=O'Connor|first5=Jingmai K.|last6=Benton|first6=Michael J.|last7=Zhang|first7=Jianping|last8=Wang|first8=Yan|last9=Tseng|first9=Kuowei|date=2016-06-28|title=Mummified precocial bird wings in mid-Cretaceous Burmese amber|journal=Nature Communications|language=en|volume=7|page=12089|doi=10.1038/ncomms12089|pmid=27352215|pmc=4931330|bibcode=2016NatCo...712089X}}</ref>

A large [[Phylogenetics|phylogenetic]] analysis of early dinosaurs by Matthew Baron, [[David B. Norman]] and Paul Barrett (2017) found that [[Theropoda]] is actually more closely related to [[Ornithischia]], to which it formed the [[sister group]] within the [[clade]] [[Ornithoscelida]]. The study also suggested that if the feather-like structures of theropods and ornithischians are of common evolutionary origin then it would be possible that feathers were restricted to Ornithoscelida. If so, then the origin of feathers would have likely occurred as early as the [[Middle Triassic]],<ref name="Ornithoscelida">{{cite journal | last1 = Baron | first1 = M.G. | last2 = Norman | first2 = D.B. | last3 = Barrett | first3 = P.M. | year = 2017 | title = A new hypothesis of dinosaur relationships and early dinosaur evolution | journal = Nature | volume = 543 | issue = 7646| pages = 501–506 | doi = 10.1038/nature21700 | pmid = 28332513 | bibcode = 2017Natur.543..501B | s2cid = 205254710 }}</ref> though this has been disagreed upon.<ref>{{Cite journal |last1=Yang |first1=Zixiao |last2=Jiang |first2=Baoyu |last3=McNamara |first3=Maria E. |last4=Kearns |first4=Stuart L. |last5=Pittman |first5=Michael |last6=Kaye |first6=Thomas G. |last7=Orr |first7=Patrick J. |last8=Xu |first8=Xing |last9=Benton |first9=Michael J. |date=December 17, 2018 |title=Pterosaur integumentary structures with complex feather-like branching |url=https://cora.ucc.ie/bitstream/handle/10468/8311/8816_Yang_et_al_2019_NEE_Pterosaur_feathers.pdf?sequence=1&isAllowed=y |journal=Nature Ecology & Evolution |language=en |volume=3 |issue=1 |pages=24–30 |doi=10.1038/s41559-018-0728-7 |pmid=30568282 |bibcode=2018NatEE...3...24Y |hdl=1983/1f7893a1-924d-4cb3-a4bf-c4b1592356e9 |s2cid=56480710 |issn=2397-334X}}</ref><ref>{{Cite journal |last1=Langer |first1=Max C. |last2=Ezcurra |first2=Martín D. |last3=Rauhut |first3=Oliver W. M. |last4=Benton |first4=Michael J. |last5=Knoll |first5=Fabien |last6=McPhee |first6=Blair W. |last7=Novas |first7=Fernando E. |last8=Pol |first8=Diego |last9=Brusatte |first9=Stephen L. |date=November 2, 2017 |title=Untangling the dinosaur family tree |url=https://research-information.bris.ac.uk/ws/files/136903911/Langer_et_al._reply_to_Baron_et_al._mjb.pdf |journal=Nature |language=en |volume=551 |issue=7678 |pages=E1–E3 |doi=10.1038/nature24011 |pmid=29094688 |bibcode=2017Natur.551E...1L |hdl=1983/d088dae2-c7fa-4d41-9fa2-aeebbfcd2fa3 |s2cid=205260354 |issn=1476-4687}}</ref> The lack of feathers present in large sauropods and ankylosaurs could be that feathers were suppressed by genomic regulators.<ref>{{Cite journal |last1=Benton |first1=Michael J. |last2=Dhouailly |first2=Danielle |last3=Jiang |first3=Baoyu |last4=McNamara |first4=Maria |date=2019-09-01 |title=The Early Origin of Feathers |url=https://cora.ucc.ie/bitstream/handle/10468/8068/10285.pdf?sequence=1 |journal=Trends in Ecology & Evolution |language=en |volume=34 |issue=9 |pages=856–869 |doi=10.1016/j.tree.2019.04.018 |pmid=31164250 |bibcode=2019TEcoE..34..856B |hdl=10468/8068 |s2cid=174811556 |issn=0169-5347}}</ref>

===Evolutionary stages===
[[File:Feather stages diagram.svg|thumb|right|Diagram illustrating stages of evolution]]
Several studies of feather development in the embryos of modern birds, coupled with the distribution of feather types among various prehistoric bird precursors, have allowed scientists to attempt a reconstruction of the sequence in which feathers first evolved and developed into the types found on modern birds.

Feather evolution was broken down into the following stages by Xu and Guo in 2009:<ref name="xu&guo2009">{{cite journal | last1 = Xu | first1 = X. | last2 = Guo | first2 = Y. | year = 2009 | title = The origin and early evolution of feathers: insights from recent paleontological and neontological data |journal = Vertebrata PalAsiatica | volume = 47 | issue = 4| pages = 311–329 }}</ref>
# Single filament
# Multiple filaments joined at their base
# Multiple filaments joined at their base to a central filament
# Multiple filaments along the length of a central filament
# Multiple filaments arising from the edge of a membranous structure
# Pennaceous feather with vane of barbs and barbules and central rachis
# Pennaceous feather with an asymmetrical rachis
# Undifferentiated vane with central rachis

However, Foth (2011) showed that some of these purported stages (stages 2 and 5 in particular) are likely simply artifacts of preservation caused by the way fossil feathers are crushed and the feather remains or imprints are preserved. Foth re-interpreted stage 2 feathers as crushed or misidentified feathers of at least stage 3, and stage 5 feathers as crushed stage 6 feathers.<ref name="foth2011">{{cite journal | last1 = Foth | first1 = C | year = 2011 | title = On the identification of feather structures in stem-line representatives of birds: evidence from fossils and actuopalaeontology | journal = Paläontologische Zeitschrift | volume =  86| pages =  91–102| doi = 10.1007/s12542-011-0111-3 | s2cid = 86362907 }}</ref>

The following simplified diagram of dinosaur relationships follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among dinosaurs and prehistoric birds. The diagram follows one presented by Xu and Guo (2009)<ref name="xu&guo2009"/> modified with the findings of Foth (2011).<ref name="foth2011"/> The numbers accompanying each name refer to the presence of specific feather stages. Note that 's' indicates the known presence of scales on the body.
<div class="noprint">{{clade| style=font-size:80%;line-height:70%
|label1=[[Dinosauria]]
|1={{clade
   |label1=[[Ornithischia]]
   |1={{clade
         |1=[[Heterodontosauridae]] (1)
         |2={{clade
            |1=[[Thyreophora]] (s)
            |2={{clade
               |1=[[Kulindadromeus]] (s, 1, 3)<ref name="Godefroit2014">{{cite journal | last1 = Godefroit | first1 = P. | last2 = Sinitsa | first2 = S.M. | last3 = Dhouailly | first3 = D. | last4 = Bolotsky | first4 = Y.L. | last5 = Sizov | first5 = A.V. | last6 = McNamara | first6 = M.E. | last7 = Benton | first7 = M.J. | last8 = Spagna | first8 = P. | year = 2014 | title = A Jurassic ornithischian dinosaur from Siberia with both feathers and scales | url = http://palaeo.gly.bris.ac.uk/Benton/reprints/2014Kulinda.pdf | journal = Science | volume = 345 | issue = 6195 | pages = 451–455 | doi = 10.1126/science.1253351 | pmid = 25061209 | bibcode = 2014Sci...345..451G | s2cid = 206556907 | access-date = 2016-07-27 | archive-url = https://web.archive.org/web/20190209232112/http://palaeo.gly.bris.ac.uk/Benton/reprints/2014Kulinda.pdf | archive-date = 2019-02-09 | url-status = dead | hdl = 1983/a7ae6dfb-55bf-4ca4-bd8b-a5ea5f323103 | hdl-access = free }}</ref>
               |2={{clade
                  |1=[[Ornithopoda]] (s)
                  |2={{clade
                     |1=[[Psittacosauridae]] (s, 1)
                     |2=[[Ceratopsidae]] (s)
                  }}
               }}
            }}
         }}
      }}
   |label2=[[Saurischia]]
   |2={{clade
      |1=[[Sauropodomorpha]] (s)
      |2={{clade
            |1={{clade
               |1=''[[Aucasaurus]]'' (s)
               |2=''[[Carnotaurus]]'' (s)
               |3=''[[Ceratosaurus]]'' (s)
               }}
            |label2=[[Coelurosauria]]
            |2={{clade
                 |1={{clade
                          |1=''[[Dilong (dinosaur)|Dilong]]'' (3?)
                          |2=Other [[Tyrannosauroidea|tyrannosauroids]] (s, 1)
                     }}
                 |2={{clade
                    |1={{clade
                       |1=''[[Juravenator]]'' (s, 3?)
                       |2=''[[Sinosauropteryx]]'' (3+)
                       }}
                     |label2=[[Maniraptora]]
                     |2={{clade
                           |1=[[Therizinosaur]]ia (1, 3+)
                           |2={{clade
                              |1=[[Alvarezsauridae]] (3?)
                              |2={{clade
                                 |1=[[Oviraptorosauria]] (4, 6)
                                 |label2=[[Paraves]]
                                 |2={{clade
                                 |1={{clade
                                    |1=[[Troodontidae]] (3+, 6)
                                        |2={{clade
                                           |1=Other dromaeosaurids
                                           |2={{clade
                                                 |1=''[[Sinornithosaurus]]'' (3+, 6)
                                                 |2=''[[Microraptor]]'' (3+, 6, 7)
                                              }}
                                           }}
                                        }}
                                       |2={{clade
                                          |1=[[Scansoriopterygidae]] (3+, 6, 8)
                                          |2={{clade
                                             |1=[[Archaeopterygidae]] (3+, 6, 7)
                                             |2={{clade
                                                |1=''[[Jeholornis]]'' (6, 7)
                                                |2={{clade
                                                      |1=''[[Confuciusornis]]'' (4, 6, 7, 8)
                                                      |2={{clade
                                                         |1=[[Enantiornithes]] (4, 6, 7, 8)
                                                         |2=[[Neornithes]] (4, 6, 7, 8)
                        }}
                     }}
                  }}
               }}
            }}
         }}
      }}
   }}
}}
}}
}}
}}
}}
}}
}}
</div>

=== In pterosaurs ===

[[Pterosaur]]s were long known to have filamentous fur-like structures covering their body known as [[pycnofibres]], which were generally considered distinct from the "true feathers" of birds and their dinosaur kin. However, a 2018 study of two small, well-preserved pterosaur fossils from the [[Jurassic]] of [[Inner Mongolia]], [[China]] indicated that pterosaurs were covered in an array of differently-structured pycnofibres (rather than just filamentous ones), with several of these structures displaying diagnostic features of feathers, such as non-veined grouped filaments and bilaterally branched filaments, both of which were originally thought to be exclusive to birds and other maniraptoran dinosaurs. Given these findings, it is possible that feathers have deep evolutionary origins in ancestral [[archosaur]]s, though there is also a possibility that these structures independently evolved to resemble bird feathers via [[convergent evolution]].<ref>{{Cite journal|last1=Unwin|first1=David M.|last2=Martill|first2=David M.|date=December 2020|title=No protofeathers on pterosaurs|url=https://www.nature.com/articles/s41559-020-01308-9|journal=Nature Ecology & Evolution|language=en|volume=4|issue=12|pages=1590–1591|doi=10.1038/s41559-020-01308-9|pmid=32989266|bibcode=2020NatEE...4.1590U |s2cid=222168569|issn=2397-334X}}</ref> Mike Benton, the study's senior author, lent credence to the former theory, stating "We couldn't find any anatomical evidence that the four pycnofiber types are in any way different from the feathers of birds and dinosaurs. Therefore, because they are the same, they must share an evolutionary origin, and that was about 250 million years ago, long before the origin of birds."<ref>{{Cite journal|last1=Yang|first1=Zixiao|last2=Jiang|first2=Baoyu|last3=McNamara|first3=Maria E.|last4=Kearns|first4=Stuart L.|last5=Pittman|first5=Michael|last6=Kaye|first6=Thomas G.|last7=Orr|first7=Patrick J.|last8=Xu|first8=Xing|last9=Benton|first9=Michael J.|date=January 2019|title=Pterosaur integumentary structures with complex feather-like branching|journal=Nature Ecology & Evolution|language=en|volume=3|issue=1|pages=24–30|doi=10.1038/s41559-018-0728-7|pmid=30568282|bibcode=2018NatEE...3...24Y |issn=2397-334X|hdl=1983/1f7893a1-924d-4cb3-a4bf-c4b1592356e9|s2cid=56480710|url=https://research-information.bris.ac.uk/ws/files/184677374/Main_Text_revised_mjb.pdf|hdl-access=free}}</ref><ref>{{Cite web|url=http://www.sci-news.com/paleontology/pterosaur-feathers-06733.html|title=Pterosaurs Had Four Types of Feathers, New Study Shows {{!}} Paleontology {{!}} Sci-News.com|website=Breaking Science News {{!}} Sci-News.com|date=18 December 2018 |language=en-US|access-date=2018-12-19}}</ref><ref name="NYT-20181217">{{cite news |last=St. Fleur |first=Nicholas |title=Feathers and Fur Fly Over Pterosaur Fossil Finding – An analysis of two fossils would push back the origins of feathers by about 70 million years, but more specimens may be needed for confirmation. |url=https://www.nytimes.com/2018/12/17/science/pterosaur-feathers-fur.html |date=17 December 2018 |work=[[The New York Times]] |access-date=19 December 2018 }}</ref><ref>{{Cite news|url=https://www.bbc.com/news/science-environment-46572782|title=Fur flies over new pterosaur fossils|last=Briggs|first=Helen|date=2018-12-17|work=BBC News|access-date=2018-12-19|language=en-GB}}</ref> But the integumentary structures of the [[anurognathid]] specimens is still based gross morphology as Liliana D'Alba pointed out. The pycnofibres of the two anurognathid specimens might not be homologous with the filamentous appendages on dinosaurs.<ref>{{Cite journal|last=D'Alba|first=Liliana|date=2019|title=Pterosaur plumage|journal=Nature Ecology & Evolution|language=en|volume=3|issue=1|pages=12–13|doi=10.1038/s41559-018-0767-0|pmid=30568284|s2cid=56480834|issn=2397-334X|doi-access=free}}</ref> Paul M. Barrett suspects that during the integumentary evolution of pterosaurs, pterosaurs primitively lost scales and pycnofibers started to appear.<ref name="youtube.com"/> 

''Cascocauda'' was almost entirely covered in an extensive coat of pycnofibres, which appear to have come in two types. The first are simple, curved filaments that range in length from 3.5–12.8 mm long. These filaments cover most of the animal, including the head, neck, body, limbs and tail. The second type consists of tufts of filaments joined near the base, similar to the branching [[down feathers]] of birds and other [[coelurosaurian]] dinosaurs, around 2.5–8.0 mm long and only cover the wing membranes. Studies of sampled pycnofibres revealed the presence of microbodies within the filaments, resembling the [[melanosome]] pigments identified in other fossil integuments, specifically phaeomelanosomes. Furthermore, [[Infrared spectroscopy|infrared spectral analysis]] of these pycnofibres show similar [[absorption spectra]] to red [[human hair]]. These pycnofibres likely provided both insulation and may have helped streamline the body and wings during flight.<ref name="pycnos">{{Cite journal|author1=Zixiao Yang |author2=Baoyu Jiang |author3=Maria E. McNamara |author4=Stuart L. Kearns |author5=Michael Pittman |author6=Thomas G. Kaye |author7=Patrick J. Orr |author8=Xing Xu |author9=Michael J. Benton |year=2019 |title=Pterosaur integumentary structures with complex feather-like branching |journal=Nature Ecology & Evolution |volume=3 |issue=1 |pages=24–30 |doi=10.1038/s41559-018-0728-7 |pmid=30568282 |bibcode=2018NatEE...3...24Y |hdl=1983/1f7893a1-924d-4cb3-a4bf-c4b1592356e9 |s2cid=56480710 |url=https://research-information.bris.ac.uk/en/publications/1f7893a1-924d-4cb3-a4bf-c4b1592356e9 |hdl-access=free }}</ref>
The identity of these branching structures as pycnofibres or feathers was challenged by Unwin & Martill (2020), who interpreted them as bunched-up and degraded aktinofibrils–stiffening fibres found in the wing membrane of pterosaurs–and attributed the melanosomes and keratin to skin rather than filaments.<ref>{{Cite journal |last1=Unwin |first1=D. M. |last2=Martill |first2=D. M. |year=2020 |title=No protofeathers on pterosaurs |journal=Nature Ecology & Evolution |volume=4 |issue= 12|pages= 1590–1591|doi=10.1038/s41559-020-01308-9 |pmid=32989266 |bibcode=2020NatEE...4.1590U |s2cid=222168569}}</ref> These claims were refuted by Yang and colleagues, who argue that Unwin and Martill's interpretations are inconsistent with the specimen's preservation. Namely, they argue that the consistent structure, regular spacing, and extension of the filaments beyond the wing membrane support their identification as pycnofibres. Further, they argue that the restriction of melanosomes and keratin to the fibres, as occurs in fossil dinosaur feathers, supports the case they are filaments and is not consistent with contamination from preserved skin.<ref>{{Cite journal |last1=Yang |first1=Z. |last2=Jiang |first2=B. |last3=McNamara |first3=M. E. |last4=Kearns |first4=S. L. |last5=Pittman |first5=M. |last6=Kaye |first6=T. G. |last7=Orr |first7=P. J. |last8=Xu |first8=X. |last9=Benton |first9=M. J. |year=2020 |title=Reply to: No protofeathers on pterosaurs |journal=Nature Ecology & Evolution |volume=4 |issue=12 |pages=1592–1593 |doi=10.1038/s41559-020-01309-8 |pmid=32989267 |bibcode=2020NatEE...4.1592Y |s2cid=222163211|hdl=10468/11874 |hdl-access=free }}</ref> Protofeathers likely evolved in early archosaurs, not long after the P-T extinction event during the time metabolic rates of early archosaurs and synapsids were increasing, postures becoming erect, and sustained activity.<ref name=":0" />