Editing Feather (section)

=== 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" />