Editing Feather (section)

=== 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>