Editing Pterosaur (section)

==Description==
[[File:Pterodactylus_BMMS7_life.png|thumb|left|Life reconstruction of ''[[Pterodactylus]]'']]
The anatomy of pterosaurs was highly modified from their reptilian ancestors by the adaptation to flight. Pterosaur [[skeleton|bones]] were hollow and air-filled, like those of [[bird]]s. This provided a higher [[muscle]] attachment surface for a given skeletal weight. The bone walls were often paper-thin. They had a large and keeled [[breastbone]] for flight muscles and an enlarged [[brain]] able to coordinate complex flying behaviour.<ref name="Witmer_et_al_2003">{{cite journal |vauthors=Witmer LM, Chatterjee S, Franzosa J, Rowe T |title=Neuroanatomy of flying reptiles and implications for flight, posture and behaviour |journal=Nature |volume=425 |issue=6961 |pages=950–53 |year=2003 |pmid=14586467 |doi=10.1038/nature02048 |bibcode=2003Natur.425..950W |s2cid=4431861 |url=http://doc.rero.ch/record/15277/files/PAL_E2576.pdf }}</ref> Pterosaur skeletons often show considerable fusion. In the skull, the [[suture (anatomy)|suture]]s between elements disappeared. In some later pterosaurs, the backbone over the shoulders fused into a structure known as a [[notarium]], which served to stiffen the torso during flight, and provide a stable support for the [[scapula|shoulder blade]]. Likewise, the sacral vertebrae could form a single [[synsacrum]] while the pelvic bones fused also.

Basal pterosaurs include the clades Dimorphodontidae (''[[Dimorphodon]]''), Campylognathididae (''[[Eudimorphodon]]'', ''[[Campylognathoides|Campyognathoides]]''), and Rhamphorhynchidae (''[[Rhamphorhynchus]]'', ''[[Scaphognathus]]'').

Pterodactyloids include the clades Ornithocheiroidea (''[[Istiodactylus]]'', ''[[Ornithocheirus]]'', ''[[Pteranodon]]''), Ctenochasmatoidea (''[[Ctenochasma]]'', ''[[Pterodactylus]]''), Dsungaripteroidea (''[[Germanodactylus]]'', ''[[Dsungaripterus]]''), and Azhdarchoidea (''[[Tapejara (pterosaur)|Tapejara]]'', ''[[Tupuxuara]]'', ''[[Quetzalcoatlus]]'').

The two groups overlapped in time, but the earliest pterosaurs in the fossil record are basal pterosaurs, and the latest pterosaurs are pterodactyloids.<ref>{{Cite web|url=https://pterosaur.net/origins.php|title=Pterosaur.net :: Origins and Relationships|website=pterosaur.net|access-date=2020-02-01}}</ref>

The position of the clade Anurognathidae (''[[Anurognathus]], [[Jeholopterus]], [[Vesperopterylus]]'') is debated.<ref>{{cite journal |last1=Andres |first1=Brian |last2=Clark |first2=James M. |last3=Xing |first3=Xu |title=A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs |journal=Journal of Vertebrate Paleontology |date=29 January 2010 |volume=30 |issue=1 |pages=163–187 |doi=10.1080/02724630903409220 |bibcode=2010JVPal..30..163A |s2cid=53688256 |url=http://doc.rero.ch/record/31614/files/PAL_E956.pdf }}</ref> Anurognathids were highly specialized. Small flyers with shortened jaws and a wide gape, some had large eyes suggesting [[nocturnal]] or [[Crepuscular animal|crepuscular]] habits, mouth bristles, and feet adapted for clinging. Parallel adaptations are seen in birds and bats that prey on insects in flight.

===Size===
{{Main|Pterosaur size}}
[[File:Size disparity of late Maastrichtian pterosaurs and birds.svg|thumb|Size disparity of late Maastrichtian Pterosaurs compared to birds and humans|250px]]
Pterosaurs had a wide range of sizes, though they were generally large. The smallest species had a wingspan no less than {{convert|25|cm|in|0|abbr=off}}.<ref name=wangetal2008>{{cite journal | last1 = Wang | first1 = X. | last2 = Kellner | first2 = A.W.A. | last3 = Zhou | first3 = Z. | last4 = Campos | first4 = D.A. | year = 2008 | title = Discovery of a rare arboreal forest-dwelling flying reptile (Pterosauria, Pterodactyloidea) from China | journal = Proceedings of the National Academy of Sciences | volume = 105 | issue = 6| pages = 1983–87 | doi = 10.1073/pnas.0707728105 | pmid=18268340 | pmc=2538868 | bibcode = 2008PNAS..105.1983W| doi-access = free }}</ref> The most sizeable forms represent the largest known animals ever to fly, with wingspans of up to {{convert|10|–|11|m|ft|abbr=off|0}}.<ref name=witton2010>{{cite journal| last1 = Witton | first1 = Mark P. | last2 = Martill | first2 = David M. | last3 = Loveridge | first3 = Robert F. | year = 2010 | title = Clipping the Wings of Giant Pterosaurs: Comments on Wingspan Estimations and Diversity | journal = Acta Geoscientica Sinica | volume = 31 | pages = 79–81}}</ref>

Standing, such giants could reach the height of a modern [[giraffe]]. Traditionally, it was assumed that pterosaurs were extremely light relative to their size. Later, it was understood that this would imply unrealistically low densities of their soft tissues. Some modern estimates therefore extrapolate a weight of up to {{convert|250|kg|lb|abbr=off}} for the largest species.{{sfn|Witton|2013|p=58}}

===Skull, teeth, and crests===
[[File:Ctenochasmatoid_skulls.jpg|thumb|left|Diagram showing specialized skulls and teeth of various [[ctenochasmatid]] pterosaurs]]
Compared to the other vertebrate flying groups, the birds and bats, pterosaur skulls were typically quite large.{{sfn|Witton|2013|p=23}} Most pterosaur skulls had elongated jaws.{{sfn|Witton|2013|p=23}} Their skull bones tend to be fused in adult individuals.{{sfn|Witton|2013|p=23}} Early pterosaurs often had [[heterodont]] teeth, varying in build, and some still had teeth in the palate. In later groups the teeth mostly became conical.<ref name=DU06b/> Front teeth were often longer, forming a "prey grab" in transversely expanded jaw tips, but size and position were very variable among species.{{sfn|Witton|2013|p=27}} With the derived [[Pterodactyloidea]], the skulls became even more elongated, sometimes surpassing the combined neck and torso in length. This was caused by a stretching and fusion of the front snout bone, the [[premaxilla]], with the upper jawbone, the [[maxilla]]. Unlike most [[archosaur]]s, the nasal and [[Antorbital fenestra|antorbital opening]]s of pterodactyloid pterosaurs merged into a single large opening, called the ''nasoantorbital fenestra''.{{sfn|Wellnhofer|1991|p=47}} This feature likely evolved to lighten the skull for flight.<ref name=DU06b/> In contrast, the bones behind the eye socket contracted and rotated, strongly inclining the rear skull and bringing the jaw joint forward.{{sfn|Witton|2013|p=26}} The [[braincase]] was relatively large for reptiles.{{sfn|Witton|2013|p=24}}
[[File:Nyctosaurus_gracilis_skull_-_Pterosaurs_Flight_in_the_Age_of_Dinosaurs.jpg|thumb|The toothless skull of ''[[Nyctosaurus]]'', bearing an enormous head crest]]
In some cases, fossilized [[keratin]]ous beak tissue has been preserved, though in toothed forms, the beak is small and restricted to the jaw tips and does not involve the teeth.<ref name="frey&martill1998">{{cite journal |vauthors=Frey E, Martill DM |title=Soft tissue preservation in a specimen of ''Pterodactylus kochi'' (Wagner) from the Upper Jurassic of Germany |journal=Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen |volume=210|issue=3 |pages=421–41 |year=1998|doi=10.1127/njgpa/210/1998/421}}</ref> Some advanced beaked forms were toothless, such as the [[Pteranodontidae]] and [[Azhdarchidae]], and had larger, more extensive, and more bird-like beaks.<ref name=DU06b/> Some groups had specialised tooth forms. The [[Istiodactylidae]] had recurved teeth for eating meat. [[Ctenochasmatidae]] used combs of numerous needle-like teeth for filter feeding; ''[[Pterodaustro]]'' could have over a thousand bristle-like teeth. [[Dsungaripteridae]] covered their teeth with jawbone tissue for a crushing function. If teeth were present, they were placed in separate tooth sockets.{{sfn|Wellnhofer|1991|p=47}} Replacement teeth were generated behind, not below, the older teeth.{{sfn|Witton|2013|p=27}}
[[File:Tapejarines mmartyniuk.png|thumb|left|[[Tapejaridae|Tapejarids]] are some of the many pterosaurs with prominent crests. Reconstruction from top to bottom: ''[[Tapejara (pterosaur)|Tapejara wellnhoferi]]'', ''[[Tupandactylus|Tupandactylus navigans]]'', ''[[Tupandactylus imperator]]'' (drawn to scale)]]
The public image of pterosaurs is defined by their elaborate head crests.{{sfn|Wellnhofer|1991|p=48}} This was influenced by the distinctive backward-pointing crest of the well-known ''[[Pteranodon]]''. The main positions of such crests are the front of the snout, as an outgrowth of the premaxillae, or the rear of the skull as an extension of the [[parietal bone]]s in which case it is called a "supraoccipital crest".{{sfn|Witton|2013|p=24}} Front and rear crests can be present simultaneously and might be fused into a single larger structure, the most expansive of which is shown by the [[Tapejaridae]]. ''[[Nyctosaurus]]'' sported a bizarre antler-like crest. The crests were only a few millimetres thin transversely. The bony crest base would typically be extended by keratinous or other soft tissue.{{sfn|Witton|2013|p=24}}

Since the 1990s, new discoveries and a more thorough study of old specimens have shown that crests are far more widespread among pterosaurs than previously assumed. That they were extended by or composed completely of keratin, which does not fossilize easily, had misled earlier research.<ref name="naish&martill2003"/> For ''[[Pterorhynchus]]'' and ''[[Pterodactylus]]'', the true extent of these crests has only been uncovered using [[ultraviolet]] photography.<ref name="frey&martill1998"/><ref name=CJ02>Czerkas, S.A., and Ji, Q. (2002). A new rhamphorhynchoid with a headcrest and complex integumentary structures. In: Czerkas, S.J. (Ed.). ''Feathered Dinosaurs and the Origin of Flight''. The Dinosaur Museum: Blanding, Utah, 15–41. {{ISBN|1-932075-01-1}}.</ref> While fossil crests used to be restricted to the more advanced Pterodactyloidea, ''Pterorhynchus'' and ''[[Austriadactylus]]'' show that even some early pterosaurs possessed them.<ref name="naish&martill2003"/>

Like the upper jaws, the paired lower jaws of pterosaurs were very elongated.{{sfn|Wellnhofer|1991|p=49}} In advanced forms, they tended to be shorter than the upper cranium because the jaw joint was in a more forward position. The front lower jaw bones, the dentaries or ''ossa dentalia'', were at the tip tightly fused into a central symphysis. This made the lower jaws function as a single connected whole, the [[mandible]]. The symphysis was often very thin transversely and long, accounting for a considerable part of the jaw length, up to 60%.{{sfn|Witton|2013|p=26}} If a crest was present on the snout, the symphysis could feature a matching mandible crest, jutting out to below.{{sfn|Witton|2013|p=26}} Toothed species also bore teeth in their dentaries. The mandible opened and closed in a simple vertical or "orthal" up-and-down movement.

===Vertebral column===
[[File:Arambourgiania philadelphiae.JPG|thumb|Elongate neck vertebra of the [[azhdarchid]] pterosaur ''[[Arambourgiania]]'']]
The [[vertebral column]] of pterosaurs numbered between thirty-four and seventy [[vertebrae]]. The vertebrae in front of the tail were "procoelous": the cotyle (front of the [[vertebral body]]) was concave and into it fitted a convex extension at the rear of the preceding vertebra, the [[condyle]]. Advanced pterosaurs are unique in possessing special processes projecting adjacent to their condyle and cotyle, the [[exapophyses]],<ref name="Bennett94">{{cite journal|author=S. Christopher Bennett|year=1994|title=Taxonomy and systematics of the Late Cretaceous pterosaur ''Pteranodon'' (Pterosauria, Pterodactyloidea)|url=https://www.biodiversitylibrary.org/page/4467188#page/5/mode/1up|journal=Occasional Papers of the Natural History Museum of the University of Kansas|volume=169|pages=1–70}}</ref> and the cotyle also may possess a small prong on its midline called a hypapophysis.{{sfn|Witton|2013|p=28}}
[[File:Anhanguera santanae - Pterosaurs Flight in the Age of Dinosaurs.jpg|left|thumb|The neck of ''Anhanguera'' was longer than the torso]]
The necks of pterosaurs were relatively long and straight. In pterodactyloids, the neck is typically longer than the torso.{{sfn|Wellnhofer|1991|p=50}} This length is not caused by an increase of the number of vertebrae, which is invariably seven. Some researchers include two transitional "cervicodorsals" which brings the number to nine.{{sfn|Wellnhofer|1991|p=50}} Instead, the vertebrae themselves became more elongated, up to eight times longer than wide. Nevertheless, the cervicals were wider than high, implying a better vertical than horizontal neck mobility. Pterodactyloids have lost all neck ribs.{{sfn|Witton|2013|p=28}} Pterosaur necks were probably rather thick and well-muscled,{{sfn|Witton|2013|p=45}} especially vertically.{{sfn|Witton|2013|p=46}}

The torso was relatively short and egg-shaped. The vertebrae in the back of pterosaurs originally might have numbered eighteen. With advanced species a growing number of these tended to be incorporated into the [[sacrum]]. Such species also often show a fusion of the front dorsal vertebrae into a rigid whole which is called the [[notarium]] after a comparable structure in birds. This was an adaptation to withstand the forces caused by flapping the wings.{{sfn|Wellnhofer|1991|p=50}} The notarium included three to seven vertebrae, depending on the species involved but also on individual age. These vertebrae could be connected by tendons or a fusion of their [[neural spine]]s into a "supraneural plate". Their ribs also would be tightly fused into the notarium.{{sfn|Witton|2013|p=30}} In general, the ribs are double headed.{{sfn|Witton|2013|p=31}} The sacrum consisted of three to ten sacral vertebrae. They too, could be connected via a supraneural plate that, however, would not contact the notarium.{{sfn|Witton|2013|p=30}}

The tails of pterosaurs were always rather slender. This means that the [[caudofemoralis]] retractor muscle which in most basal [[Archosauria]] provides the main propulsive force for the hindlimb, was relatively unimportant.{{sfn|Witton|2013|p=46}} The tail vertebrae were amphicoelous, the vertebral bodies on both ends being concave. Early species had long tails, containing up to fifty caudal vertebrae, the middle ones stiffened by elongated articulation processes, the [[zygapophyses]], and [[Chevron (anatomy)|chevron]]s.{{sfn|Wellnhofer|1991|p=51}} Such tails acted as rudders, sometimes ending at the rear in a vertical diamond-shaped or oval vane.{{sfn|Wellnhofer|1991|p=52}} In pterodactyloids, the tails were much reduced and never stiffened,{{sfn|Wellnhofer|1991|p=52}} with some species counting as few as ten vertebrae.{{sfn|Witton|2013|p=30}}

===Shoulder girdle===
[[File:UCMP Pteranodon dorsal body.JPG|thumb|The shoulder girdle connected to the notarium]]
The [[shoulder girdle]] was a strong structure that transferred the forces of flapping flight to the [[thorax]]. It was probably covered by thick muscle layers.{{sfn|Witton|2013|p=44}} The upper bone, the [[shoulder blade]], was a straight bar. It was connected to a lower bone, the [[coracoid]] that is relatively long in pterosaurs. In advanced species, their combined whole, the scapulocoracoid, was almost vertically oriented. The shoulder blade in that case fitted into a recess in the side of the notarium, while the coracoid likewise connected to the breastbone. This way, both sides together made for a rigid closed loop, able to withstand considerable forces.{{sfn|Witton|2013|p=31}} A peculiarity was that the breastbone connections of the coracoids often were asymmetrical, with one coracoid attached in front of the other. In advanced species the shoulder joint had moved from the shoulder blade to the coracoid.{{sfn|Witton|2013|p=32}} The joint was saddle-shaped and allowed considerable movement to the wing.{{sfn|Witton|2013|p=31}} It faced sideways and somewhat upwards.{{sfn|Wellnhofer|1991|p=52}}

The breastbone, formed by fused paired ''sterna'', was wide. It had only a shallow keel. Via sternal ribs, it was at its sides attached to the dorsal ribs.{{sfn|Wellnhofer|1991|p=51}} At its rear, a row of belly ribs or [[gastralia]] was present, covering the entire belly.{{sfn|Wellnhofer|1991|p=52}} To the front, a long point, the ''cristospina'', jutted obliquely upwards. The rear edge of the breastbone was the deepest point of the thorax.{{sfn|Witton|2013|p=32}} Clavicles or interclavicles were completely absent.{{sfn|Wellnhofer|1991|p=52}}

===Wings===
[[File:Pterosaur wing configurations.jpg|thumb|left|Various configurations proposed for the wings of pterosaurs]]
Pterosaur wings were formed by bones and membranes of skin and other tissues. The primary membranes attached to the extremely long fourth [[finger]] of each [[arm]] and extended along the sides of the body. Where they ended has been very controversial but since the 1990s a dozen specimens with preserved soft tissue have been found that seem to show they attached to the ankles. The exact curvature of the trailing edge, however, is still equivocal.{{sfn|Witton|2013|p=54}}
[[File:Cast of Rhamphorhynchus muensteri 02 - Pterosaurs Flight in the Age of Dinosaurs.jpg|thumb|Some specimens, such as this ''[[Rhamphorhynchus]]'',  preserve the membrane structure]]
While historically thought of as simple leathery structures composed of skin, research has since shown that the wing membranes of pterosaurs were highly complex dynamic structures suited to an active style of flight.{{sfn|Witton|2013|p=53}} The outer wings (from the tip to the elbow) were strengthened by closely spaced fibers called ''[[actinofibrils]]''.<ref>{{cite journal |author=Bennett SC |title=Pterosaur flight: the role of actinofibrils in wing function |journal=Historical Biology |volume=14 |issue=4 |pages=255–84 |year=2000 |doi=10.1080/10292380009380572|bibcode=2000HBio...14..255B |s2cid=85185457 }}</ref> The actinofibrils themselves consisted of three distinct layers in the wing, forming a crisscross pattern when superimposed on one another. The function of the actinofibrils is unknown, as is the exact material from which they were made. Depending on their exact composition (keratin, muscle, elastic structures, etc.), they may have been stiffening or strengthening agents in the outer part of the wing.<ref name=kellneretal2009/> The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.<ref name="naish&martill2003">{{cite journal |vauthors=Naish D, Martill DM |title=Pterosaurs – a successful invasion of prehistoric skies |journal=Biologist |volume=50 |issue=5 |pages=213–16 |year=2003}}</ref> The combination of actinofibrils and muscle layers may have allowed the animal to adjust the wing slackness and [[Camber (aerodynamics)|camber]].{{sfn|Witton|2013|p=53}}

As shown by cavities in the wing bones of larger species and soft tissue preserved in at least one specimen, some pterosaurs extended their system of respiratory [[air sacs]] into the wing membrane.<ref name=claessensetal2009>{{cite journal |vauthors=Claessens LP, O'Connor PM, Unwin DM |title=Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism |journal=PLOS ONE |volume=4 |issue=2 |pages=e4497 |year=2009 |pmid=19223979 |pmc=2637988 |doi=10.1371/journal.pone.0004497 |editor1-last=Sereno |editor1-first=Paul |bibcode=2009PLoSO...4.4497C|doi-access=free }}</ref>

====Parts of the wing====
[[File:Pterosaur wing surfaces (labeled).png|thumb|left|Two pterosaurs (''[[Scaphognathus]]'' and ''[[Balaenognathus]]'') in dorsal view, with wing parts labeled<br><br />('''bp''': brachiopatagium, '''cp''': cruropatagium, '''pp''': propatagium)]]
The pterosaur wing membrane is divided into three basic units.{{sfn|Witton|2013|p=52}} The first, called the ''propatagium'' ("fore membrane"), was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight. The ''[[patagium|brachiopatagium]]'' ("arm membrane") was the primary component of the wing, stretching from the highly elongated fourth finger of the hand to the hindlimbs. Finally, at least some pterosaur groups had a membrane that stretched between the legs, possibly connecting to or incorporating the tail, called the '''uropatagium''';{{sfn|Witton|2013|p=52}} the extent of this membrane is not certain, as studies on ''[[Sordes]]'' seem to suggest that it simply connected the legs but did not involve the tail (rendering it a '''cruropatagium'''). A common interpretation is that [[Rhamphorhynchoidea|non-pterodactyloid]] pterosaurs had a broader uro/cruropatagium stretched between their long fifth toes, with pterodactyloids, lacking such toes, only having membranes running along the legs.{{sfn|Witton|2013|p=55}}
[[File:SordesDB.jpg|thumb|right|''[[Sordes]]'', as depicted here, evidences the possibility that pterosaurs had a ''cruro''patagium – a membrane connecting the legs that, unlike the [[Bat|chiropteran]] ''uro''patagium, leaves the tail free]]
There has been considerable argument among paleontologists about whether the main wing membranes (brachiopatagia) attached to the hindlimbs, and if so, where. Fossils of the rhamphorhynchoid ''[[Sordes]]'',<ref name=Unwin_Bakhurina_1994>{{cite journal |vauthors=Unwin DM, Bakhurina NN |title=''Sordes pilosus'' and the nature of the pterosaur flight apparatus |journal=Nature |volume=371 |issue= 6492|pages=62–64 |year=1994 |doi=10.1038/371062a0|bibcode=1994Natur.371...62U |s2cid=4314989 }}</ref> the [[anurognathid]] ''[[Jeholopterus]]'',<ref>{{cite journal |vauthors=Wang X, Zhou Z, Zhang F, Xu X |title=A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and "hairs" from Inner Mongolia, northeast China |journal=Chinese Science Bulletin |volume=47 |page=3 |year=2002 |doi=10.1360/02tb9054 |issue=3 |doi-broken-date=4 December 2024 |bibcode=2002ChSBu..47..226W|s2cid=86641794 }}</ref> and a pterodactyloid from the [[Santana Formation]] seem to demonstrate that the wing membrane did attach to the hindlimbs, at least in some species.<ref>{{cite journal|year=2003|title= New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion |journal=Geological Society, London, Special Publications|doi=10.1144/GSL.SP.2003.217.01.14|last1=Frey|first1=E.|last2=Tischlinger|first2=H.|last3=Buchy|first3=M.-C.|last4=Martill|first4=D. M.|volume=217|issue= 1 |pages=233–66|bibcode= 2003GSLSP.217..233F |s2cid= 130462931 }}</ref> However, modern [[bat]]s and [[flying squirrel]]s show considerable variation in the extent of their wing membranes and it is possible that, like these groups, different species of pterosaur had different wing designs. Indeed, analysis of pterosaur limb proportions shows that there was considerable variation, possibly reflecting a variety of wing-plans.<ref>{{cite journal |vauthors=Dyke GJ, Nudds RL, Rayner JM |title=Limb disparity and wing shape in pterosaurs |journal=J. Evol. Biol. |volume=19 |issue=4 |pages=1339–42 |date=July 2006 |pmid=16780534 |doi=10.1111/j.1420-9101.2006.01096.x|s2cid=30516133 |doi-access=free }}</ref>

The bony elements of the arm formed a mechanism to support and extend the wing. Near the body, the [[humerus]] or upper arm bone is short but powerfully built.{{sfn|Wellnhofer|1991|p=53}} It sports a large deltopectoral crest, to which the major flight muscles are attached.{{sfn|Wellnhofer|1991|p=53}} Despite the considerable forces exerted on it, the humerus is hollow or pneumatised inside, reinforced by bone struts.{{sfn|Witton|2013|p=32}} The long bones of the lower arm, the [[ulna]] and [[Radius (bone)|radius]], are much longer than the humerus.{{sfn|Witton|2013|p=33}} They were probably incapable of [[pronation]].

A bone unique to pterosaurs,{{sfn|Witton|2013|p=34}} known as the pteroid, connected to the wrist and helped to support the forward membrane (the propatagium) between the wrist and shoulder. Evidence of webbing between the three free fingers of the pterosaur forelimb suggests that this forward membrane may have been more extensive than the simple pteroid-to-shoulder connection traditionally depicted in life restorations.<ref name="naish&martill2003"/> The position of the pteroid bone itself has been controversial. Some scientists, notably Matthew Wilkinson, have argued that the pteroid pointed forward, extending the forward membrane and allowing it to function as an adjustable [[Flap (aeronautics)|flap]].<ref name="Wilkinson MT, Unwin DM, Ellington CP 2006 119–26">{{cite journal |vauthors=Wilkinson MT, Unwin DM, Ellington CP |title=High lift function of the pteroid bone and forewing of pterosaurs |journal=[[Proceedings of the Royal Society B]] |volume=273 |issue=1582 |pages=119–26 |year=2006 |pmid=16519243 |pmc=1560000 |doi=10.1098/rspb.2005.3278}}</ref> This view was contradicted in a 2007 paper by Chris Bennett, who showed that the pteroid did not articulate as previously thought and could not have pointed forward, but rather was directed inward toward the body as traditionally interpreted.<ref>{{cite journal |author=Bennett SC |title=Articulation and Function of the Pteroid Bone of Pterosaurs |journal=Journal of Vertebrate Paleontology |volume=27 |issue=4 |pages=881–91 |year=2007 |doi=10.1671/0272-4634(2007)27[881:AAFOTP]2.0.CO;2|s2cid=86326537 |url=http://doc.rero.ch/record/15676/files/PAL_E854.pdf }}</ref>  Specimens of ''[[Changchengopterus|Changchengopterus pani]]'' and ''[[Darwinopterus|Darwinopterus linglongtaensis]]'' show the pteroid in articulation with the proximal syncarpal, suggesting that the pteroid articulated with the 'saddle' of the radiale (proximal syncarpal) and that both the pteroid and preaxial carpal were migrated centralia.<ref name=zhouschoch>{{cite journal | first1= Chang-Fu | last1 = Zhou | first2 = Rainer R. | last2 = Schoch | year = 2011 | title = New material of the non-pterodactyloid pterosaur Changchengopterus pani Lü, 2009 from the Late Jurassic Tiaojishan Formation of western Liaoning | journal = Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen | volume = 260 | issue = 3 | pages = 265–75 | doi = 10.1127/0077-7749/2011/0131}}</ref><ref name=wangetal2010>{{cite journal | first1 = Xiao-Lin | last1 = Wang | first2 = Alexander W. A. | last2 = Kellner | first3 = Shun-Xing | last3 = Jiang | first4 = Xin | last4 = Cheng | first5 = Xi | last5 = Meng | first6 = Taissa | last6 = Rodrigues | year = 2010 | title = New long-tailed pterosaurs (Wukongopteridae) from western Liaoning, China | journal = Anais da Academia Brasileira de Ciências | volume = 82 | issue = 4 | pages = 1045–62 | doi=10.1590/s0001-37652010000400024| doi-access = free | pmid = 21152776 }}</ref>
[[File:Pteranodon_amnh_martyniuk.jpg|thumb|left|Some advanced pterosaurs such as ''[[Pteranodon]]'' had highly elongate wings]]
The pterosaur wrist consists of two inner (proximal, at the side of the long bones of the arm) and four outer (distal, at the side of the hand) carpals (wrist bones), excluding the pteroid bone, which may itself be a modified distal carpal. The proximal carpals are fused together into a "syncarpal" in mature specimens, while three of the distal carpals fuse to form a distal syncarpal. The remaining distal carpal, referred to here as the medial carpal, but which has also been termed the distal lateral, or pre-axial carpal, articulates on a vertically elongate biconvex facet on the anterior surface of the distal syncarpal. The medial carpal bears a deep concave fovea that opens anteriorly, ventrally and somewhat medially, within which the pteroid articulates, according to Wilkinson.<ref name=wilkinsonetal2006>{{cite journal |author1=Wilkinson M.T. |author2=Unwin D.M. |author3=Ellington C.P. | year = 2006 | title = High lift function of the pteroid bone and forewing of pterosaurs | journal = [[Proceedings of the Royal Society B]] | volume = 273 | issue = 1582| pages = 119–26 | doi = 10.1098/rspb.2005.3278 | pmid=16519243 | pmc = 1560000}}</ref>

In derived pterodactyloids like [[pteranodontia]]ns and [[azhdarchoid]]s, metacarpals I-III are small and do not connect to the carpus, instead hanging in contact with the fourth metacarpal.{{sfn|Witton|2013|p=35}} With these derived species, the fourth metacarpal has been enormously elongated, typically equalling or exceeding the length of the long bones of the lower arm.{{sfn|Wellnhofer|1991|p=55}} The fifth metacarpal had been lost.{{sfn|Wellnhofer|1991|p=53}} In all species, the first to third fingers are much smaller than the fourth, the "wingfinger", and contain two, three and four phalanges respectively.{{sfn|Witton|2013|p=35}} The smaller fingers are clawed, with the ungual size varying among species. In [[nyctosaurid]]s the forelimb digits besides the wingfinger have been lost altogether. The wingfinger accounts for about half or more of the total wing length.{{sfn|Witton|2013|p=35}} It normally consists of four phalanges. Their relative lengths tend to vary among species, which has often been used to distinguish related forms.{{sfn|Witton|2013|p=35}} The fourth phalanx is usually the shortest. It lacks a claw and has been lost completely by nyctosaurids. It is curved to behind, resulting in a rounded wing tip, which reduces [[induced drag]]. The wingfinger is also bent somewhat downwards.{{sfn|Wellnhofer|1991|p=55}}

When standing, pterosaurs probably rested on their metacarpals, with the outer wing folded to behind. In this position, the "anterior" sides of the metacarpals were rotated to the rear. This would point the smaller fingers obliquely to behind. According to Bennett, this would imply that the wingfinger, able to describe the largest arc of any wing element, up to 175°, was not folded by flexion but by an extreme extension. The wing was automatically folded when the elbow was bowed.{{sfn|Witton|2013|p=46}}{{sfn|Wellnhofer|1991|pp=53–54}}

A laser-simulated fluorescence scan on ''[[Pterodactylus]]'' also identified a membranous "fairing" (area conjunctioning the wing with the body at the neck), as opposed to the feathered or fur-composed "fairing" seen in birds and bats respectively.<ref>{{Cite journal|doi = 10.1073/pnas.2107631118|issn=0027-8424 |title = Pterosaurs evolved a muscular wing–body junction providing multifaceted flight performance benefits: Advanced aerodynamic smoothing, sophisticated wing root control, and wing force generation|year = 2021|last1 = Pittman|first1 = Michael|last2 = Barlow|first2 = Luke A.|last3 = Kaye|first3 = Thomas G.|last4 = Habib|first4 = Michael B.|journal = Proceedings of the National Academy of Sciences|volume = 118|issue = 44|pages = e2107631118|pmid = 34663691|pmc = 8612209|bibcode = 2021PNAS..11807631P|s2cid = 239028043|doi-access=free }}</ref>

===Pelvis===
[[File:Anhanguera-santanae sacrum.jpg|thumb|An [[anhanguerid]] pelvis seen from above, with the right side rotated towards the viewer]]
The [[pelvis]] of pterosaurs was of moderate size compared to the body as a whole. Often the three pelvic bones were fused.{{sfn|Wellnhofer|1991|p=55}} The [[Ilium (bone)|ilium]] was long and low, its front and rear blades projecting horizontally beyond the edges of the lower pelvic bones. Despite this length, the rod-like form of these processes indicates that the hindlimb muscles attached to them were limited in strength.{{sfn|Witton|2013|p=46}} The, in side view narrow, [[pubic bone]] fused with the broad [[ischium]] into an ischiopubic blade. Sometimes, the blades of both sides were also fused, closing the pelvis from below and forming the pelvic canal. The [[hip joint]] was not perforated and allowed considerable mobility to the leg.{{sfn|Witton|2013|p=35}} It was directed obliquely upwards, preventing a perfectly vertical position of the leg.{{sfn|Wellnhofer|1991|p=55}}

The front of the pubic bones articulated with a unique structure, the paired prepubic bones. Together these formed a cusp covering the rear belly, between the pelvis and the belly ribs. The vertical mobility of this element suggests a function in breathing, compensating the relative rigidity of the chest cavity.{{sfn|Witton|2013|p=35}}

===Hindlimbs===
[[File:Dsungaripterus_weii_01.jpg|thumb|left|Some pterosaurs such as ''[[Dsungaripterus]]'' had developed hindlimbs, and were likely highly capable walkers and runners]]
The hindlimbs of pterosaurs were strongly built, yet relative to their wingspans smaller than those of birds. They were long in comparison to the torso length.{{sfn|Wellnhofer|1991|p=56}} The thighbone was rather straight, with the head making only a small angle with the shaft.{{sfn|Witton|2013|p=35}} This implies that the legs were not held vertically below the body but were somewhat sprawling.{{sfn|Wellnhofer|1991|p=56}} The shinbone was often fused with the upper ankle bones into a tibiotarsus that was longer than the thighbone.{{sfn|Wellnhofer|1991|p=56}} It could attain a vertical position when walking.{{sfn|Wellnhofer|1991|p=56}} The calf bone tended to be slender, especially at its lower end that in advanced forms did not reach the ankle, sometimes reducing total length to a third. Typically, it was fused to the shinbone.{{sfn|Witton|2013|p=35}} The ankle was a simple, "mesotarsal", hinge.{{sfn|Wellnhofer|1991|p=56}} The, rather long and slender,{{sfn|Wellnhofer|1991|p=57}} [[metatarsus]] was always splayed to some degree.{{sfn|Witton|2013|p=36}} The foot was plantigrade, meaning that during the walking cycle the sole of the metatarsus was pressed onto the soil.{{sfn|Wellnhofer|1991|p=57}}

There was a clear difference between early pterosaurs and advanced species regarding the form of the fifth digit. Originally, the fifth [[metatarsal]] was robust and not very shortened. It was connected to the ankle in a higher position than the other metatarsals.{{sfn|Wellnhofer|1991|p=57}} It bore a long, and often curved, mobile clawless fifth toe consisting of two phalanges.{{sfn|Witton|2013|p=36}} The function of this element has been enigmatic. It used to be thought that the animals slept upside-down like bats, hanging from branches and using the fifth toes as hooks. Another hypothesis held that they stretched the brachiopatagia, but in articulated fossils the fifth digits are always flexed towards the tail.{{sfn|Wellnhofer|1991|p=57}} Later it became popular to assume that these toes extended an uropatagium or cruropatagium between them. As the fifth toes were on the outside of the feet, such a configuration would only have been possible if these rotated their fronts outwards in flight.{{sfn|Wellnhofer|1991|p=57}} Such a rotation could be caused by an [[Abduction (anatomy)|abduction]] of the thighbone, meaning that the legs would be spread. This would also turn the feet into a vertical position.{{sfn|Wellnhofer|1991|p=57}} They then could act as rudders to control yaw. Some specimens show membranes between the toes,<ref name="witton&naish2008"/> allowing them to function as flight control surfaces. The uropatagium or cruropatagium would control pitch. When walking the toes could flex upwards to lift the membrane from the ground. In Pterodactyloidea, the fifth metatarsal was much reduced and the fifth toe, if present, little more than a stub.{{sfn|Witton|2013|p=37}} This suggests that their membranes were split, increasing flight maneuverability.{{sfn|Witton|2013|p=55}}

The first to fourth toes were long. They had two, three, four and five phalanges respectively.{{sfn|Wellnhofer|1991|p=56}} Often the third toe was longest; sometimes the fourth. Flat joints indicate a limited mobility. These toes were clawed but the claws were smaller than the hand claws.{{sfn|Witton|2013|p=36}}

===Soft tissues===
The rare conditions that allowed for the fossilisation of pterosaur remains, sometimes also preserved soft tissues. Modern [[synchrotron]] or ultraviolet light photography has revealed many traces not visible to the naked eye.{{sfn|Witton|2013|p=39}} These are often imprecisely called "impressions" but mostly consist of [[petrification]]s, natural casts and transformations of the original material. They may include horn crests, beaks or claw sheaths as well as the various flight membranes. Exceptionally, muscles were preserved.{{sfn|Witton|2013|p=43}} Skin patches show small round non-overlapping scales on the soles of the feet, the ankles and the ends of the [[metatarsal bones|metatarsals]].{{sfn|Witton|2013|p=47}} They covered pads cushioning the impact of walking. Scales are unknown from other parts of the body.{{sfn|Witton|2013|p=48}}

====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.