Editing Pterosaur (section)

====Pycnofibers====
[[File:Sordes pilosus.jpg|thumb|''Sordes'' preserved pycnofibers]]
Most or all pterosaurs had [[hair]]-like filaments known as pycnofibers on the head and torso.{{sfn|Witton|2013|p=51}} The term "pycnofiber", meaning "dense filament", was coined by palaeontologist [[Alexander Kellner]] and colleagues in 2009.<ref name=kellneretal2009>{{cite journal | last1 = Kellner | first1 = A.W.A. | last2 = Wang | first2 = X. | last3 = Tischlinger | first3 = H. | last4 = Campos | first4 = D. | last5 = Hone | first5 = D.W.E. | last6 = Meng | first6 = X. | year = 2009 | title = The soft tissue of ''Jeholopterus'' (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane | journal = Proceedings of the Royal Society B | volume = 277| issue = 1679| pages = 321–29| doi = 10.1098/rspb.2009.0846 | pmid = 19656798 | pmc=2842671}}</ref> Pycnofibers were unique structures similar to, but not [[homology (biology)|homologous]] (sharing a common origin) with, [[mammal]]ian hair, an example of [[convergent evolution]].<ref name=Unwin_Bakhurina_1994/> A fuzzy [[integument]] was first reported from a specimen of ''[[Scaphognathus crassirostris]]'' in 1831 by [[Georg August Goldfuss]],<ref>{{cite journal | last1 = Goldfuss | first1 = A | year = 1831 | title = Beiträge zur Erkentniss verschiedner Reptilien der Vorwelt | journal = Nova Acta Academiae Leopoldinae | volume = 15 | pages = 61–128 }}</ref> but had been widely doubted. Since the 1990s, pterosaur finds and [[histology|histological]] and ultraviolet examination of pterosaur specimens have provided incontrovertible proof: pterosaurs had pycnofiber coats. ''[[Sordes|Sordes pilosus]]'' (which translates as "hairy demon") and ''[[Jeholopterus|Jeholopterus ninchengensis]]'' show pycnofibers on the head and body.

The presence of pycnofibers strongly indicates that pterosaurs were [[endotherm]]ic (warm-blooded). They aided thermoregulation, as is common in warm-blooded animals who need insulation to prevent excessive heat-loss.{{sfn|Witton|2013|p=51}} Pycnofibers were flexible, short filaments, about five to seven millimetres long and rather simple in structure with a hollow central canal.{{sfn|Witton|2013|p=51}} Pterosaur pelts might have been comparable in density to many Mesozoic mammals.{{efn|See the [[Mammal expansion|expansion of ecological niches in the Mesozoic]]}}{{sfn|Witton|2013|p=51}}
[[File:Life_reconstruction_of_Sinomacrops_bondei.png|thumb|left|Specimens of [[anurognathid]] pterosaurs (''[[Sinomacrops]]'' pictured) were the first to indicate complex feather-like structures in pterosaurs]]
Pterosaur filaments could share a common origin with feathers, as speculated in 2002 by Czerkas and Ji.<ref name=CJ02/> In 2009, Kellner concluded that pycnofibers were structured similarly to theropod [[Evolution of the feather|proto-feathers]].<ref name="kellneretal2009" /> Others were unconvinced, considering the difference with the "quills" found on many of the bird-like [[maniraptoran]] specimens too fundamental.{{sfn|Witton|2013|p=51}}

A 2018 study of the remains of two small [[Jurassic]]-age pterosaurs from [[Inner Mongolia]], [[China]], found that pterosaurs had a wide array of pycnofiber shapes and structures, as opposed to the homogeneous structures that had generally been assumed to cover them. Some of these had frayed ends, very similar in structure to four different feather types known from birds or other dinosaurs but almost never known from pterosaurs prior to the study, suggesting homology.<ref name="Benton2019">{{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. |title=Pterosaur integumentary structures with complex feather-like branching |journal=Nature Ecology & Evolution |date=January 2019 |volume=3 |issue=1 |pages=24–30 |doi=10.1038/s41559-018-0728-7 |pmid=30568282 |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><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}}</ref> A response to this study was published in 2020, where it was suggested that the structures seen on the [[Anurognathidae|anurognathids]] were actually a result of the decomposition of aktinofibrils: a type of fibre used to strengthen and stiffen the wing.<ref>{{cite journal |last1=Unwin |first1=David M. |last2=Martill |first2=David M. |title=No protofeathers on pterosaurs |journal=Nature Ecology & Evolution |date=December 2020 |volume=4 |issue=12 |pages=1590–1591 |doi=10.1038/s41559-020-01308-9 |pmid=32989266 |bibcode=2020NatEE...4.1590U |s2cid=222168569 }}</ref> However, in a response to this, the authors of the 2018 paper point to the fact that the presence of the structures extend past the [[patagium]], and the presence of both aktinofibrils and filaments on ''[[Jeholopterus|Jeholopterus ningchengensis]]''<ref>{{Cite journal|last=Kellner |display-authors=et al |date=2009|title=The Soft Tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the Structure of the Pterosaur Wing Membrane|url= |journal= Proceedings of the Royal Society B: Biological Sciences|volume=277 |issue=1679 |pages=321–29|doi=10.1098/rspb.2009.0846 |pmid=19656798 |pmc=2842671 }}</ref> and ''[[Sordes|Sordes pilosus]]''.<ref>{{cite journal |last1=Unwin |first1=David M. |last2=Bakhurina |first2=Natasha N. |title=Sordes pilosus and the nature of the pterosaur flight apparatus |journal=Nature |date=September 1994 |volume=371 |issue=6492 |pages=62–64 |doi=10.1038/371062a0 |bibcode=1994Natur.371...62U |s2cid=4314989 }}</ref> The various forms of filament structure present on the anurognathids in the 2018 study would also require a form of decomposition that would cause the different 'filament' forms seen. They therefore conclude that the most parsimonious interpretation of the structures is that they are filamentous protofeathers.<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. |title=Reply to: No protofeathers on pterosaurs |journal=Nature Ecology & Evolution |date=December 2020 |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> But Liliana D'Alba points out that the description of the preserved integumentary structures on the two anurognathid specimens is still based upon gross morphology. She also points out that ''Pterorhynchus'' was described to have feathers to support the claim that feathers had a common origin with Ornithodirans but was argued against by several authors. The only method to assure if it was homologous to feathers is to use a scanning electron microscope.<ref>{{cite journal |last1=D’Alba |first1=Liliana |title=Pterosaur plumage |journal=Nature Ecology & Evolution |date=January 2019 |volume=3 |issue=1 |pages=12–13 |doi=10.1038/s41559-018-0767-0 |pmid=30568284 |s2cid=56480834 |doi-access=free }}</ref>

In 2022, a new fossil of ''[[Tupandactylus|Tupandactylus cf. imperator]]''<ref>{{Cite journal|last=Cincotta |display-authors=et al |date=2022|title=Pterosaur melanosomes support signalling functions for early feathers|url=|journal=Nature|volume=604 |issue= 7907|pages=684–688|doi=10.1038/s41586-022-04622-3 |pmid= 35444275|pmc= 9046085|bibcode=2022Natur.604..684C }}</ref> was found to have melanosomes in forms that signal an earlier-than-anticipated development of patterns found in extant feathers. The new specimen suggested that pterosaur integumentary melanosomes exhibited a more complex organization than those previously known from other pterosaurs. This indicates the presence of a unique form of melanosomes within pterosaur integument at the time, distinct from previously known contemporary integumentary structures and more similar to those reported from mammalian hair and avian feathers. The feather fossils obtained from this specimen also suggest the presence of Stage IIIa feathers, a new discovery that indicates more complex feather structures were present in pterosaurs. The study describing this specimen further clarifies the timeline of avian feather evolution and suggests that the feather-specific melanosome signaling found in extant birds are possibly homologous with those found in pterosaurs.