Pterosaurs[b][c] are an extinctclade of flying reptiles in theorderPterosauria. They existed during most of theMesozoic: from the LateTriassic to the end of theCretaceous (228 million to 66 million years ago).[8] Pterosaurs are the earliestvertebrates known to have evolvedpowered flight. Their wings were formed by a membrane of skin, muscle, and othertissues stretching from the ankles to a dramatically lengthened fourth finger.[9]
There were two major types of pterosaurs. Basal pterosaurs (also called 'non-pterodactyloid pterosaurs' or 'rhamphorhynchoids') were smaller animals with fully toothed jaws and, typically, long tails. Their wide wing membranes probably included and connected the hind legs. On the ground, they would have had an awkward sprawling posture, but the anatomy of their joints and strong claws would have made them effective climbers, and some may have even lived in trees. Basal pterosaurs wereinsectivores orpredators of small vertebrates. Later pterosaurs (pterodactyloids) evolved many sizes, shapes, and lifestyles. Pterodactyloids had narrower wings with free hind limbs, highly reduced tails, and long necks with large heads. On the ground, they walked well on all four limbs with an upright posture, standingplantigrade on the hind feet and folding the wing finger upward to walk on the three-fingered "hand". They could take off from the ground, and fossil trackways show that at least some species were able to run, wade, and/or swim.[10] Their jaws had horny beaks, and some groups lacked teeth. Some groups developed elaborate head crests withsexual dimorphism.
Pterosaurs sported coats of hair-like filaments known aspycnofibers, which covered their bodies and parts of their wings. Pycnofibers grew in several forms, from simple filaments to branching downfeathers. These may behomologous to the down feathers found on bothavian and some non-aviandinosaurs, suggesting that early feathers evolved in the common ancestor of pterosaurs and dinosaurs, possibly as insulation.[11] They were warm-blooded (endothermic), active animals. Therespiratory system had efficient unidirectional "flow-through" breathing usingair sacs, which hollowed out their bones to an extreme extent. Pterosaurs spanned a wide range ofadult sizes, from the very smallanurognathids to the largest known flying creatures, includingQuetzalcoatlus andHatzegopteryx,[12][13][14] which reached wingspans of at least nine metres. The combination ofendothermy, a good oxygen supply and strong muscles made pterosaurs powerful and capable flyers.
Pterosaurs are often referred to by popular media or the general public as "flying dinosaurs", but dinosaurs are defined as the descendants of thelast common ancestor of theSaurischia andOrnithischia, which excludes the pterosaurs.[15] Pterosaurs are nonetheless more closely related to birds and other dinosaurs than to crocodiles or any other living reptile, though they are not bird ancestors. Pterosaurs are also colloquially referred to aspterodactyls, particularly in fiction and journalism.[16] However, technically,pterodactyl may refer to members of the genusPterodactylus, and more broadly to members of the suborderPterodactyloidea of the pterosaurs.[17]
Pterosaurs had a variety of lifestyles. Traditionally seen as fish-eaters, the group is now understood to have also included hunters of land animals, insectivores, fruit eaters and even predators of other pterosaurs. They reproduced byeggs, some fossils of which have been discovered.[18]
The anatomy of pterosaurs was highly modified from their reptilian ancestors by the adaptation to flight. Pterosaurbones were hollow and air-filled, like those ofbirds. This provided a highermuscle attachment surface for a given skeletal weight. The bone walls were often paper-thin. They had a large and keeledbreastbone for flight muscles and an enlargedbrain able to coordinate complex flying behaviour.[19] Pterosaur skeletons often show considerable fusion. In the skull, thesutures between elements disappeared. In some later pterosaurs, the backbone over the shoulders fused into a structure known as anotarium, which served to stiffen the torso during flight, and provide a stable support for theshoulder blade. Likewise, the sacral vertebrae could form a singlesynsacrum while the pelvic bones fused also.
The two groups overlapped in time, but the earliest pterosaurs in the fossil record are basal pterosaurs, and the latest pterosaurs are pterodactyloids.[20]
The position of the clade Anurognathidae (Anurognathus,Jeholopterus,Vesperopterylus) is debated.[21] Anurognathids were highly specialized. Small flyers with shortened jaws and a wide gape, some had large eyes suggestingnocturnal orcrepuscular habits, mouth bristles, and feet adapted for clinging. Parallel adaptations are seen in birds and bats that prey on insects in flight.
Size disparity of late Maastrichtian Pterosaurs compared to birds and humans
Pterosaurs had a wide range of sizes, though they were generally large. The smallest species had a wingspan no less than 25 centimetres (10 inches).[12] The most sizeable forms represent the largest known animals ever to fly, with wingspans of up to 10–11 metres (33–36 feet).[22]
Standing, such giants could reach the height of a moderngiraffe. 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 250 kilograms (550 pounds) for the largest species.[23]
Diagram showing specialized skulls and teeth of variousctenochasmatid pterosaurs
Compared to the other vertebrate flying groups, the birds and bats, pterosaur skulls were typically quite large.[24] Most pterosaur skulls had elongated jaws.[24] Their skull bones tend to be fused in adult individuals.[24] Early pterosaurs often hadheterodont teeth, varying in build, and some still had teeth in the palate. In later groups the teeth mostly became conical.[25] Front teeth were often longer, forming a "prey grab" in transversely expanded jaw tips, but size and position were very variable among species.[26] With the derivedPterodactyloidea, 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, thepremaxilla, with the upper jawbone, themaxilla. Unlike mostarchosaurs, the nasal andantorbital openings of pterodactyloid pterosaurs merged into a single large opening, called thenasoantorbital fenestra.[27] This feature likely evolved to lighten the skull for flight.[25] In contrast, the bones behind the eye socket contracted and rotated, strongly inclining the rear skull and bringing the jaw joint forward.[28] Thebraincase was relatively large for reptiles.[29]
The toothless skull ofNyctosaurus, bearing an enormous head crest
In some cases, fossilizedkeratinous 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.[30] Some advanced beaked forms were toothless, such as thePteranodontidae andAzhdarchidae, and had larger, more extensive, and more bird-like beaks.[25] Some groups had specialised tooth forms. TheIstiodactylidae 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.[27] Replacement teeth were generated behind, not below, the older teeth.[26]
The public image of pterosaurs is defined by their elaborate head crests.[31] This was influenced by the distinctive backward-pointing crest of the well-knownPteranodon. 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 theparietal bones in which case it is called a "supraoccipital crest".[29] 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 theTapejaridae.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.[29]
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.[32] ForPterorhynchus andPterodactylus, the true extent of these crests has only been uncovered usingultraviolet photography.[30][33] While fossil crests used to be restricted to the more advanced Pterodactyloidea,Pterorhynchus andAustriadactylus show that even some early pterosaurs possessed them.[32]
Like the upper jaws, the paired lower jaws of pterosaurs were very elongated.[34] 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 orossa dentalia, were at the tip tightly fused into a central symphysis. This made the lower jaws function as a single connected whole, themandible. The symphysis was often very thin transversely and long, accounting for a considerable part of the jaw length, up to 60%.[28] If a crest was present on the snout, the symphysis could feature a matching mandible crest, jutting out to below.[28] Toothed species also bore teeth in their dentaries. The mandible opened and closed in a simple vertical or "orthal" up-and-down movement.
Thevertebral column of pterosaurs numbered between thirty-four and seventyvertebrae. The vertebrae in front of the tail were "procoelous": the cotyle (front of thevertebral body) was concave and into it fitted a convex extension at the rear of the preceding vertebra, thecondyle. Advanced pterosaurs are unique in possessing special processes projecting adjacent to their condyle and cotyle, theexapophyses,[35] and the cotyle also may possess a small prong on its midline called a hypapophysis.[36]
The neck ofAnhanguera was longer than the torso
The necks of pterosaurs were relatively long and straight. In pterodactyloids, the neck is typically longer than the torso.[37] 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.[37] 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.[36] Pterosaur necks were probably rather thick and well-muscled,[38] especially vertically.[39]
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 thesacrum. Such species also often show a fusion of the front dorsal vertebrae into a rigid whole which is called thenotarium after a comparable structure in birds. This was an adaptation to withstand the forces caused by flapping the wings.[37] 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 theirneural spines into a "supraneural plate". Their ribs also would be tightly fused into the notarium.[40] In general, the ribs are double headed.[41] 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.[40]
The tails of pterosaurs were always rather slender. This means that thecaudofemoralis retractor muscle which in most basalArchosauria provides the main propulsive force for the hindlimb, was relatively unimportant.[39] 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, thezygapophyses, andchevrons.[42] Such tails acted as rudders, sometimes ending at the rear in a vertical diamond-shaped or oval vane.[43] In pterodactyloids, the tails were much reduced and never stiffened,[43] with some species counting as few as ten vertebrae.[40]
Theshoulder girdle was a strong structure that transferred the forces of flapping flight to thethorax. It was probably covered by thick muscle layers.[44] The upper bone, theshoulder blade, was a straight bar. It was connected to a lower bone, thecoracoid 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.[41] 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.[45] The joint was saddle-shaped and allowed considerable movement to the wing.[41] It faced sideways and somewhat upwards.[43]
The breastbone, formed by fused pairedsterna, was wide. It had only a shallow keel. Via sternal ribs, it was at its sides attached to the dorsal ribs.[42] At its rear, a row of belly ribs orgastralia was present, covering the entire belly.[43] To the front, a long point, thecristospina, jutted obliquely upwards. The rear edge of the breastbone was the deepest point of the thorax.[45] Clavicles or interclavicles were completely absent.[43]
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 fourthfinger of eacharm 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.[46]
Some specimens, such as thisRhamphorhynchus, 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.[47] The outer wings (from the tip to the elbow) were strengthened by closely spaced fibers calledactinofibrils.[48] 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.[49] The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.[32] The combination of actinofibrils and muscle layers may have allowed the animal to adjust the wing slackness andcamber.[47]
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 respiratoryair sacs into the wing membrane.[50]
The pterosaur wing membrane is divided into three basic units.[51] The first, called thepropatagium ("fore membrane"), was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight. Thebrachiopatagium ("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 theuropatagium;[51] the extent of this membrane is not certain, as studies onSordes seem to suggest that it simply connected the legs but did not involve the tail (rendering it acruropatagium). A common interpretation is thatnon-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.[52]
Sordes, as depicted here, evidences the possibility that pterosaurs had acruropatagium – a membrane connecting the legs that, unlike thechiropteranuropatagium, 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 rhamphorhynchoidSordes,[53] theanurognathidJeholopterus,[54] and a pterodactyloid from theSantana Formation seem to demonstrate that the wing membrane did attach to the hindlimbs, at least in some species.[55] However, modernbats andflying squirrels 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.[56]
The bony elements of the arm formed a mechanism to support and extend the wing. Near the body, thehumerus or upper arm bone is short but powerfully built.[57] It sports a large deltopectoral crest, to which the major flight muscles are attached.[57] Despite the considerable forces exerted on it, the humerus is hollow or pneumatised inside, reinforced by bone struts.[45] The long bones of the lower arm, theulna andradius, are much longer than the humerus.[58] They were probably incapable ofpronation.
A bone unique to pterosaurs,[59] 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.[32] 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 adjustableflap.[60] 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.[61] Specimens ofChangchengopterus pani andDarwinopterus 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.[62][63]
Some advanced pterosaurs such asPteranodon 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.[64]
In derived pterodactyloids likepteranodontians andazhdarchoids, metacarpals I-III are small and do not connect to the carpus, instead hanging in contact with the fourth metacarpal.[65] 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.[66] The fifth metacarpal had been lost.[57] In all species, the first to third fingers are much smaller than the fourth, the "wingfinger", and contain two, three and four phalanges respectively.[65] The smaller fingers are clawed, with the ungual size varying among species. Innyctosaurids the forelimb digits besides the wingfinger have been lost altogether. The wingfinger accounts for about half or more of the total wing length.[65] It normally consists of four phalanges. Their relative lengths tend to vary among species, which has often been used to distinguish related forms.[65] 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 reducesinduced drag. The wingfinger is also bent somewhat downwards.[66]
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.[39][67]
A laser-simulated fluorescence scan onPterodactylus 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.[68]
Ananhanguerid pelvis seen from above, with the right side rotated towards the viewer
Thepelvis of pterosaurs was of moderate size compared to the body as a whole. Often the three pelvic bones were fused.[66] Theilium 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.[39] The, in side view narrow,pubic bone fused with the broadischium into an ischiopubic blade. Sometimes, the blades of both sides were also fused, closing the pelvis from below and forming the pelvic canal. Thehip joint was not perforated and allowed considerable mobility to the leg.[65] It was directed obliquely upwards, preventing a perfectly vertical position of the leg.[66]
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.[65]
Some pterosaurs such asDsungaripterus 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.[69] The thighbone was rather straight, with the head making only a small angle with the shaft.[65] This implies that the legs were not held vertically below the body but were somewhat sprawling.[69] The shinbone was often fused with the upper ankle bones into a tibiotarsus that was longer than the thighbone.[69] It could attain a vertical position when walking.[69] 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.[65] The ankle was a simple, "mesotarsal", hinge.[69] The, rather long and slender,[70]metatarsus was always splayed to some degree.[71] The foot was plantigrade, meaning that during the walking cycle the sole of the metatarsus was pressed onto the soil.[70]
There was a clear difference between early pterosaurs and advanced species regarding the form of the fifth digit. Originally, the fifthmetatarsal was robust and not very shortened. It was connected to the ankle in a higher position than the other metatarsals.[70] It bore a long, and often curved, mobile clawless fifth toe consisting of two phalanges.[71] 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.[70] 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.[70] Such a rotation could be caused by anabduction of the thighbone, meaning that the legs would be spread. This would also turn the feet into a vertical position.[70] They then could act as rudders to control yaw. Some specimens show membranes between the toes,[72] 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.[73] This suggests that their membranes were split, increasing flight maneuverability.[52]
The first to fourth toes were long. They had two, three, four and five phalanges respectively.[69] 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.[71]
The rare conditions that allowed for the fossilisation of pterosaur remains, sometimes also preserved soft tissues. Modernsynchrotron or ultraviolet light photography has revealed many traces not visible to the naked eye.[74] These are often imprecisely called "impressions" but mostly consist ofpetrifications, 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.[75] Skin patches show small round non-overlapping scales on the soles of the feet, the ankles and the ends of themetatarsals.[76] They covered pads cushioning the impact of walking. Scales are unknown from other parts of the body.[77]
Most or all pterosaurs hadhair-like filaments known as pycnofibers on the head and torso.[78] The term "pycnofiber", meaning "dense filament", was coined by palaeontologistAlexander Kellner and colleagues in 2009.[49] Pycnofibers were unique structures similar to, but nothomologous (sharing a common origin) with,mammalian hair, an example ofconvergent evolution.[53] A fuzzyintegument was first reported from a specimen ofScaphognathus crassirostris in 1831 byGeorg August Goldfuss,[79] but had been widely doubted. Since the 1990s, pterosaur finds andhistological and ultraviolet examination of pterosaur specimens have provided incontrovertible proof: pterosaurs had pycnofiber coats.Sordes pilosus (which translates as "hairy demon") andJeholopterus ninchengensis show pycnofibers on the head and body.
The presence of pycnofibers strongly indicates that pterosaurs wereendothermic (warm-blooded). They aided thermoregulation, as is common in warm-blooded animals who need insulation to prevent excessive heat-loss.[78] Pycnofibers were flexible, short filaments, about five to seven millimetres long and rather simple in structure with a hollow central canal.[78] Pterosaur pelts might have been comparable in density to many Mesozoic mammals.[d][78]
Specimens ofanurognathid 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.[33] In 2009, Kellner concluded that pycnofibers were structured similarly to theropodproto-feathers.[49] Others were unconvinced, considering the difference with the "quills" found on many of the bird-likemaniraptoran specimens too fundamental.[78]
A 2018 study of the remains of two smallJurassic-age pterosaurs fromInner 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.[80][81] A response to this study was published in 2020, where it was suggested that the structures seen on theanurognathids were actually a result of the decomposition of aktinofibrils: a type of fibre used to strengthen and stiffen the wing.[82] However, in a response to this, the authors of the 2018 paper point to the fact that the presence of the structures extend past thepatagium, and the presence of both aktinofibrils and filaments onJeholopterus ningchengensis[83] andSordes pilosus.[84] 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.[85] 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 thatPterorhynchus 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.[86]
In 2022, a new fossil ofTupandactylus cf. imperator[87] 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.
Pterosaurfossils are very rare, due to their light bone construction. Complete skeletons can generally only be found in geological layers with exceptional preservation conditions, the so-calledLagerstätten. The pieces from one suchLagerstätte, theLate JurassicSolnhofen Limestone inBavaria,[88] became much sought after by rich collectors.[89] In 1784, Italian naturalistCosimo Alessandro Collini was the first scientist to describe a pterosaur fossil.[90] At that time the concepts of evolution and extinction were imperfectly developed. The bizarre build of the pterosaur was shocking, as it could not clearly be assigned to any existing animal group.[91] The discovery of pterosaurs would thus play an important role in the progress of modern paleontology and geology.[92] Scientific opinion at the time was that if such creatures were still alive, only the sea was a credible habitat; Collini suggested it might be a swimming animal that used its long front limbs as paddles.[93] A few scientists continued to support the aquatic interpretation even until 1830, when German zoologistJohann Georg Wagler suggested thatPterodactylus used its wings as flippers and was affiliated withIchthyosauria andPlesiosauria.[94]
Newman's marsupial pterosaurs
In 1800,Johann Hermann first suggested that it represented a flying creature in a letter toGeorges Cuvier. Cuvier agreed in 1801, understanding it was an extinct flying reptile.[95] In 1809, he coined the namePtéro-Dactyle, "wing-finger".[96] This was in 1815 Latinised toPterodactylus.[97] At first most species were assigned to this genus and ultimately "pterodactyl" was popularly and incorrectly applied to all members of Pterosauria.[16] Today, paleontologists limit the term to the genusPterodactylus or members of thePterodactyloidea.[17]
In 1812 and 1817,Samuel Thomas von Soemmerring redescribed the original specimen and an additional one.[98] He saw them as affiliated to birds and bats. Although he was mistaken in this, his "bat model" would be influential during the 19th century.[99] In 1843,Edward Newman thought pterosaurs were flyingmarsupials.[100] Ironically, as the "bat model" depicted pterosaurs as warm-blooded and furred, it would turn out to be more correct in certain aspects than Cuvier's "reptile model" in the long run. In 1834,Johann Jakob Kaup coined the term Pterosauria.[101]
Historical reconstruction ofDimorphodon as a biped by Seeley
In 1828,Mary Anning found in England the first pterosaur genus outside Germany,[102] named asDimorphodon byRichard Owen, also the first non-pterodactyloid pterosaur known.[103] Later in the century, theEarly CretaceousCambridge Greensand produced thousands of pterosaur fossils, that however, were of poor quality, consisting mostly of strongly eroded fragments.[104] Nevertheless, based on these, numerous genera and species would be named.[92] Many were described byHarry Govier Seeley, at the time the main English expert on the subject, who also wrote the first pterosaur book,Ornithosauria,[105] and in 1901 the first popular book,[92]Dragons of the Air. Seeley thought that pterosaurs were warm-blooded and dynamic creatures, closely related to birds.[106] Earlier, the evolutionistSt. George Jackson Mivart had suggested pterosaurs were the direct ancestors of birds.[107] Owen opposed the views of both men, seeing pterosaurs as cold-blooded "true" reptiles.[108]
In the US,Othniel Charles Marsh in 1870 discoveredPteranodon in theNiobrara Chalk, then the largest known pterosaur,[108] the first toothless one and the first from America.[109] These layers too rendered thousands of fossils,[109] also including relatively complete skeletons that were three-dimensionally preserved instead of being strongly compressed as with the Solnhofen specimens. This led to a much better understanding of many anatomical details,[109] such as the hollow nature of the bones.
Meanwhile, finds from the Solnhofen had continued, accounting for the majority of complete high-quality specimens discovered.[110] They allowed to identify most new basal taxa, such asRhamphorhynchus,Scaphognathus andDorygnathus.[110] This material gave birth to a German school of pterosaur research, which saw flying reptiles as the warm-blooded, furry and active Mesozoic counterparts of modern bats and birds.[111] In 1882, Marsh andKarl Alfred Zittel published studies about the wing membranes of specimens ofRhamphorhynchus.[112][113] German studies continued well into the 1930s, describing new species such asAnurognathus. In 1927,Ferdinand Broili discovered hair follicles in pterosaur skin,[114] andpaleoneurologistTilly Edinger determined that the brains of pterosaurs more resembled those of birds than modern cold-blooded reptiles.[115]
In contrast, English and American paleontologists by the middle of the twentieth century largely lost interest in pterosaurs. They saw them as failed evolutionary experiments, cold-blooded and scaly, that hardly could fly, the larger species only able to glide, being forced to climb trees or throw themselves from cliffs to achieve a take-off. In 1914, for the first-time pterosaur aerodynamics were quantitatively analysed, byErnest Hanbury Hankin andDavid Meredith Seares Watson, but they interpretedPteranodon as a pure glider.[116] Little research was done on the group during the 1940s and 1950s.[92]
This drawing ofZhejiangopterus by John Conway exemplifies the "new look" of pterosaurs
The situation for dinosaurs was comparable. From the 1960s onwards, adinosaur renaissance took place, a quick increase in the number of studies and critical ideas, influenced by the discovery of additional fossils ofDeinonychus, whose spectacular traits refuted what had become entrenched orthodoxy. In 1970, likewise the description of the furry pterosaurSordes began whatRobert Bakker named a renaissance of pterosaurs.[117]Kevin Padian especially propagated the new views, publishing a series of studies depicting pterosaurs as warm-blooded, active and running animals.[118][119][120] This coincided with a revival of the German school through the work ofPeter Wellnhofer, who in 1970s laid the foundations of modern pterosaur science.[88] In 1978, he published the first pterosaur textbook,[121] theHandbuch der Paläoherptologie, Teil 19: Pterosauria,[122] and in 1991 the second ever popular science pterosaur book,[121] theEncyclopedia of Pterosaurs.[123]
This development accelerated through the exploitation of two newLagerstätten.[121] During the 1970s, the Early CretaceousSantana Formation in Brazil began to produce chalk nodules that, though often limited in size and the completeness of the fossils they contained, perfectly preserved three-dimensional pterosaur skeletal parts.[121] German and Dutch institutes bought such nodules from fossil poachers and prepared them in Europe, allowing their scientists to describe many new species and revealing a whole new fauna. Soon, Brazilian researchers, among themAlexander Kellner, intercepted the trade and named even more species.
Even more productive was the Early Cretaceous ChineseJehol Biota ofLiaoning that since the 1990s has brought forth hundreds of exquisitely preserved two-dimensional fossils, often showing soft tissue remains. Chinese researchers such asLü Junchang have again named many new taxa. As discoveries also increased in other parts of the world, a sudden surge in the total of named genera took place. By 2009, when they had increased to about ninety, this growth showed no sign of levelling-off.[124] In 2013, M.P. Witton indicated that the number of discovered pterosaur species had risen to 130.[125] Over ninety percent of known taxa has been named during the "renaissance". Many of these were from groups the existence of which had been unknown.[121] Advances in computing power enabled researchers to determine their complex relationships through thequantitative method ofcladistics. New and old fossils yielded much more information when subjected to modern ultraviolet light or roentgen photography, orCAT-scans.[126] Insights from other fields of biology were applied to the data obtained.[126] All this resulted in a substantial progress in pterosaur research, rendering older accounts in popular science books completely outdated.
In 2017 a fossil from a 170-million-year-old pterosaur, later named as the speciesDearc sgiathanach in 2022, was discovered on theIsle of Skye inScotland. TheNational Museum of Scotland claims that it is the largest of its kind ever discovered from theJurassic period, and it has been described as the world's best-preserved skeleton of a pterosaur.[127]
Because pterosauranatomy has been so heavily modified for flight, and immediatetransitional fossil predecessors have not so far been described, the ancestry of pterosaurs is not fully understood.[128] The oldest known pterosaurs were already fully adapted to a flying lifestyle. Since Seeley, it was recognised that pterosaurs were likely to have had their origin in the "archosaurs", what today would be called theArchosauromorpha. In the 1980s, early cladistic analyses found that they wereAvemetatarsalians (archosaurs closer todinosaurs than tocrocodilians). As this would make them also rather close relatives of the dinosaurs, these results were seen by Kevin Padian as confirming his interpretation of pterosaurs as bipedal warm-blooded animals. Because these early analyses were based on a limited number of taxa and characters, their results were inherently uncertain.[129]
Several influential researchers who rejected Padian's conclusions offered alternative hypotheses.David Unwin proposed an ancestry among the basal Archosauromorpha, specifically long-necked forms ("protorosaurs") such astanystropheids. A placement amongbasal archosauriforms likeEuparkeria was also suggested.[25] Basal archosauromorps such as these seemed to be good candidates for close pterosaur relatives due to their long-limbed anatomy; especially notable isSharovipteryx, which possessed skin membranes on its hindlimbs likely used for gliding.[129] A 1999 study byMichael Benton reinforced that pterosaurs were avemetatarsalians closely related toScleromochlus, and named the group Ornithodira to encompass pterosaurs and dinosaurs.[130] In 1996, research S. Christopher Bennett published an analysis finding pterosaurs to be protorosaurs or closely related to them after removing characteristics of the hindlimb from his analysis, to test the possibility of locomotion-basedconvergent evolution between pterosaurs anddinosaurs.[131] A 2007 reply by Dave Hone and Michael Benton could not reproduce this result, finding pterosaurs to be closely related to dinosaurs even without hindlimb characters. They concluded that, although more basal pterosauromorphs are needed to clarify their relationships, current evidence indicates that pterosaurs are avemetatarsalians, as either the sister group ofScleromochlus or a branch between the latter andLagosuchus.[132]
A 2011 archosaur-focused phylogenetic analysis bySterling Nesbitt benefited from far more data and found strong support for pterosaurs being avemetatarsalians, thoughScleromochlus was not included due to its poor preservation.[133] A 2016 archosauromorph-focused study byMartin Ezcurra included various proposed pterosaur relatives, yet also found pterosaurs to be closer to dinosaurs and unrelated to more basal taxa.[134] Working from his 1996 analysis, Bennett published a 2020 study onScleromochlus which argued that bothScleromochlus and pterosaurs were non-archosaur archosauromorphs, albeit not particularly closely related to each other.[135] By contrast, a later 2020 study proposed thatlagerpetidarchosaurs were the sister clade to pterosauria.[136] This was based on newly described fossilskulls andforelimbs showing variousanatomical similarities with pterosaurs and reconstructions of lagerpetidbrains andsensory systems based onCT scans also showingneuroanatomical similarities with pterosaurs.[137][138] The results of the latter study were subsequently supported by an independent analysis of early pterosauromorph interrelationships.[139]
A related problem is the origin of pterosaur flight.[140] Like with birds, hypotheses can be ordered into two main varieties: "ground up" or "tree down". Climbing a tree would cause height and gravity to provide both the energy and a strongselection pressure for incipient flight.[clarification needed]Rupert Wild in 1983 proposed a hypothetical "propterosaurus": a lizard-like arboreal animal developing a membrane between its limbs, first to safely parachute and then, gradually elongating the fourth finger, to glide.[141] However, subsequent cladistic results did not fit this model well. Neither protorosaurs nor ornithodirans are biologically equivalent to lizards. Furthermore, the transition between gliding and flapping flight is not well-understood. More recent studies on basal pterosaur hindlimb morphology seem to vindicate a connection toScleromochlus. Like this archosaur, basal pterosaur lineages have plantigrade hindlimbs that show adaptations for saltation.[142]
At least one study found that the early TriassicichnofossilProrotodactylus is anatomically similar to that of early pterosaurs.[136]
It was once thought that competition with earlybird species might have resulted in theextinction of many of the pterosaurs.[143] It was thought that by the end of the Cretaceous, only large species of pterosaurs were present (no longer true; see below). The smaller species were thought to have become extinct, their niche filled by birds.[144] However, pterosaur decline (if actually present) seems unrelated to bird diversity, as ecological overlap between the two groups appears to be minimal.[145] In fact, at least some avian niches were reclaimed by pterosaurs prior to theCretaceous–Paleogene extinction event.[146] It seems that the K-Pg extinction event at the end of the Cretaceous, which wiped out all non-avian dinosaurs and many other animals, was the direct cause of the extinction of the pterosaurs.
Small-sized pterosaur species apparently were present in theCsehbánya Formation, indicating a higher diversity of Late Cretaceous pterosaurs than previously accounted for.[147] The recent findings of a smallcat-sized adult azhdarchid further indicate that small pterosaurs from the Late Cretaceous might actually have simply been rarely preserved in the fossil record, helped by the fact that there is a strong bias against terrestrial small sized vertebrates such as juveniledinosaurs, and that their diversity might actually have been much larger than previously thought.[148]
A 2021 study showcases that niches previously occupied by small pterosaurs were increasingly occupied by the juvenile stages of larger species in the Late Cretaceous. Rather than being outcompeted by birds, pterosaurs essentially specialized a trend already occurring in previous eras of the Mesozoic.[149]
Fossil ofEudimorphodon, one of the most primitive pterosaurs
Inphylogenetic taxonomy, theclade Pterosauria has usually been defined as node-based and anchored to several extensively studied taxa as well as those thought to be primitive. One 2003 study defined Pterosauria as "The most recent common ancestor of the Anurognathidae,Preondactylus andQuetzalcoatlus and all their descendants."[150] However, these types of definition would inevitably leave any related species that are slightly more primitive out of the Pterosauria. To remedy this, a new definition was proposed that would anchor the name not to any particular species but to an anatomical feature, the presence of an enlarged fourth finger that supports a wing membrane.[151] This "apomorophy-based" definition was adopted by thePhyloCode in 2020 as "[T]he clade characterized by the apomorphy fourth manual digit hypertrophied to support a wing membrane, as inherited byPterodactylus (originallyOrnithocephalus)antiquus (Sömmerring 1812)".[152] A broader clade,Pterosauromorpha, has been defined as allornithodirans more closely related to pterosaurs than todinosaurs.[153]
The internalclassification of pterosaurs has historically been difficult, because there were many gaps in thefossil record. Starting from the 21st century, new discoveries are now filling in these gaps and giving a better picture of the evolution of pterosaurs. Traditionally, they were organized into twosuborders: theRhamphorhynchoidea, a "primitive" group of long-tailed pterosaurs, and thePterodactyloidea, "advanced" pterosaurs with short tails.[25] However, this traditional division has been largely abandoned. Rhamphorhynchoidea is aparaphyletic (unnatural) group, since the pterodactyloids evolved directly from them and not from a common ancestor, so, with the increasing use ofcladistics, it has fallen out of favor among most scientists.[125][154]
The precise relationships between pterosaurs is still unsettled. Many studies of pterosaur relationships in the past have included limited data and were highly contradictory. However, newer studies using larger data sets are beginning to make things clearer. Thecladogram (family tree) below follows aphylogenetic analysis presented by Longrich, Martill and Andres in 2018, with clade names after Andreset al. (2014).[1][146]
Diagrams showing breathing motion (top two) and internal air sac system (bottom two)
The mechanics of pterosaur flight are not completely understood or modeled at this time.[155][156][needs update]
Katsufumi Sato, a Japanese scientist, did calculations using modern birds and concluded that it was impossible for a pterosaur to stay aloft.[155] In the bookPosture, Locomotion, and Paleoecology of Pterosaurs it is theorized that they were able to fly due to the oxygen-rich, dense atmosphere of theLate Cretaceous period.[157] However, both Sato and the authors ofPosture, Locomotion, and Paleoecology of Pterosaurs based their research on the now-outdated theories of pterosaurs being seabird-like, and the size limit does not apply to terrestrial pterosaurs, such asazhdarchids andtapejarids. Furthermore,Darren Naish concluded that atmospheric differences between the present and the Mesozoic were not needed for the giant size of pterosaurs.[158]
Another issue that has been difficult to understand is how theytook off. Earlier suggestions were that pterosaurs were largely cold-blooded gliding animals, deriving warmth from the environment like modern lizards, rather than burning calories. In this case, it was unclear how the larger ones of enormous size, with an inefficient cold-blooded metabolism, could manage a bird-like takeoff strategy, using only the hind limbs to generate thrust for getting airborne. Later research shows them instead as being warm-blooded and having powerful flight muscles, and using the flight muscles for walking as quadrupeds.[159]Mark Witton of theUniversity of Portsmouth and Mike Habib ofJohns Hopkins University suggested that pterosaurs used a vaulting mechanism to obtain flight.[160] The tremendous power of their winged forelimbs would enable them to take off with ease.[159] Once aloft, pterosaurs could reach speeds of up to 120 km/h (75 mph) and travel thousands of kilometres.[160]
In 1985, the Smithsonian Institution commissioned aeronautical engineerPaul MacCready to build a half-scale working model ofQuetzalcoatlus northropi. The replica was launched with a ground-based winch. It flew several times in 1986 and was filmed as part of the Smithsonian's IMAX filmOn the Wing.[161][162]
A 2009 study showed that pterosaurs had a lung-and-air-sac system and a precisely controlled skeletal breathing pump, which supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The presence of asubcutaneous air sac system in at least some pterodactyloids would have further reduced the density of the living animal.[50] Like modern crocodilians, pterosaurs appeared to have had ahepatic piston, seeing as their shoulder-pectoral girdles were too inflexible to move the sternum as in birds, and they possessed stronggastralia.[164] Thus, their respiratory system had characteristics comparable to both modern archosaur clades.
An X-ray study of pterosaurbrain cavities revealed that the animals (Rhamphorhynchus muensteri andAnhanguera santanae) had massive flocculi. Theflocculus is a brain region that integrates signals from joints, muscles, skin and balance organs.[19] The pterosaurs' flocculi occupied 7.5% of the animals' total brain mass, more than in any other vertebrate. Birds have unusually large flocculi compared with other animals, but these only occupy between 1 and 2% of total brain mass.[19]
The flocculus sends out neural signals that produce small, automatic movements in the eye muscles. These keep the image on an animal's retina steady. Pterosaurs may have had such a large flocculus because of their large wing size, which would mean that there was a great deal more sensory information to process.[19] The low relative mass of the flocculi in birds is also a result of birds having a much larger brain overall; though this has been considered an indication that pterosaurs lived in a structurally simpler environment or had less complex behaviour compared to birds,[165] recent studies of crocodilians and other reptiles show that it is common forsauropsids to achieve high intelligence levels with small brains.[166] Studies on the endocast ofAllkaruen show that brain evolution inpterodactyloids was a modular process.[167]
Thefossil trackways show that pterosaurs likeHatzegopteryx were quadrupeds, and some rather efficient terrestrial predators.
Pterosaurs' hip sockets are oriented facing slightly upwards, and the head of thefemur (thigh bone) is only moderately inward facing, suggesting that pterosaurs had an erect stance. It would have been possible to lift the thigh into a horizontal position during flight, as gliding lizards do.
There was considerable debate whether pterosaurs ambulated asquadrupeds or asbipeds. In the 1980s, paleontologistKevin Padian suggested that smaller pterosaurs with longer hindlimbs, such asDimorphodon, might have walked or even run bipedally, in addition to flying, likeroad runners.[120] However, a large number of pterosaurtrackways were later found with a distinctive four-toed hind foot and three-toed front foot; these are the unmistakable prints of pterosaurs walking on all fours.[168][169]
Fossil footprints show that pterosaurs stood with the entire foot in contact with the ground (plantigrade), in a manner similar to many mammals likehumans andbears. Footprints fromazhdarchids and several unidentified species show that pterosaurs walked with an erect posture with their four limbs held almost vertically beneath the body, an energy-efficient stance used by most modern birds and mammals, rather than the sprawled limbs of modern reptiles.[72][159] Indeed, erect-limbs may be omnipresent in pterosaurs.[142]
Though traditionally depicted as ungainly and awkward when on the ground, the anatomy of some pterosaurs (particularly pterodactyloids) suggests that they were competent walkers and runners.[170] Early pterosaurs have long been considered particularly cumbersome locomotors due to the presence of largecruropatagia, but they too appear to have been generally efficient on the ground.[142]
The forelimb bones ofazhdarchids andornithocheirids were unusually long compared to other pterosaurs, and, in azhdarchids, the bones of the arm and hand (metacarpals) were particularly elongated. Furthermore, as a whole, azhdarchid front limbs were proportioned similarly to fast-runningungulate mammals. Their hind limbs, on the other hand, were not built for speed, but they were long compared with most pterosaurs, and allowed for a long stride length. While azhdarchid pterosaurs probably could not run, they would have been relatively fast and energy efficient.[72]
The relative size of the hands and feet in pterosaurs (by comparison with modern animals such as birds) may indicate the type of lifestyle pterosaurs led on the ground. Azhdarchid pterosaurs had relatively small feet compared to their body size and leg length, with foot length only about 25–30% the length of the lower leg. This suggests that azhdarchids were better adapted to walking on dry, relatively solid ground.Pteranodon had slightly larger feet (47% the length of thetibia), while filter-feeding pterosaurs like thectenochasmatoids had very large feet (69% of tibial length inPterodactylus, 84% inPterodaustro), adapted to walking in soft muddy soil, similar to modern wading birds.[72] Though clearly forelimb-based launchers, basal pterosaurs have hindlimbs well adapted for hopping, suggesting a connection with archosaurs such asScleromochlus.[142]
Tracks made by ctenochasmatoids indicate that these pterosaurs swam using their hindlimbs. In general, these have large hindfeet and long torsos, indicating that they were probably more adapted for swimming than other pterosaurs.[171] Pteranodontians conversely have several speciations in their humeri interpreted to have been suggestive of a water-based version of the typical quadrupedal launch, and several likeboreopterids must have foraged while swimming, as they seem incapable offrigatebird-like aerial hawking.[171] These adaptations are also seen in terrestrial pterosaurs likeazhdarchids, which presumably still needed to launch from water in case they found themselves in it. ThenyctosauridAlcione may display adaptations for wing-propelled diving like moderngannets andtropicbirds.[146]
Modern interpretations of the diet ofDimorphodon have challenged traditional ideas of all pterosaurs being piscivorous
Traditionally, almost all pterosaurs were seen as surface-feeding piscivores or fish-eaters, a view that still dominates popular science. Today, many pterosaurs groups are thought to have been terrestrial carnivores, omnivores or insectivores.
Early-on it was recognised that the smallAnurognathidae were nocturnal, aerial insectivores. With highly flexible joints on the wing finger, a broad, triangular wing shape, large eyes and short tail, these pterosaurs were likely analogous tonightjars or extant insectivorous bats, being capable of high manoeuvrability at relatively low speeds.[172]
Interpretations of the habits of basal groups have changed profoundly.Dimorphodon, envisioned as apuffin analogue in the past, is indicated by its jaw structure, gait, and poor flight capabilities, as a terrestrial/semiarboreal predator of small mammals,squamates, and large insects.[173] Its robust dentition causedCampylognathoides to be seen as a generalist or a terrestrial predator of small vertebrates, but the highly robust humerus and high-aspect wing morphology, suggest it may have been capable of grabbing prey on the wing;[174] a later study indicates it wasteuthophagous based on squid findings within its gut.[175] The small insectivorousCarniadactylus and the largerEudimorphodon were highly aerial animals and fast, agile flyers with long robust wings.Eudimorphodon has been found with fish remains in its stomach, but its dentition suggests an opportunistic diet. Slender-wingedAustriadactylus andCaviramus were likely terrestrial/semiarboreal generalists.Caviramus likely had a strong bite force, indicating an adaptation towards hard food items that might have been chewed in view of the tooth wear.[176]
SomeRhamphorhynchidae, such asRhamphorhynchus itself orDorygnathus, were fish-eaters with long, slender wings, needle-like dentition and long, thin jaws.Sericipterus,Scaphognathus andHarpactognathus had more robust jaws and teeth (which were ziphodont, dagger-shaped, in Sericipterus), and shorter, broader wings. These were either terrestrial/aerial predators of vertebrates[177] orcorvid-like generalists.[178]Wukongopteridae likeDarwinopterus were first considered aerial predators. Lacking a robust jaw structure or powerful flying muscles, they are now seen as arboreal or semiterrestrial insectivores.Darwinopterus robustidens, in particular, seems to have been a beetle specialist.[179]
Among pterodactyloids, a greater variation in diet is present.Pteranodontia contained many piscivorous taxa, such as theOrnithocheirae,Boreopteridae,Pteranodontidae and Nyctosauridae.Niche partitioning caused ornithocheirans and the later nyctosaurids to be aerial dip-feeders like today'sfrigatebirds (with the exception of the plunge-diving adaptedAlcione elainus), while boreopterids were freshwater diving animals similar tocormorants, and pteranodonts pelagic plunge-divers akin toboobies andgannets. An analysis ofLonchodraco found clusters offoramina at the tip of its beak; birds with similarly numerous foramina have sensitive beaks used to feel for food, soLonchodraco may have used its beak to feel for fish or invertebrates in shallow water.[180] Theistiodactylids were likely primarily scavengers.[181]Archaeopterodactyloidea obtained food in coastal or freshwater habitats.Germanodactylus andPterodactylus were piscivores, while theCtenochasmatidae were suspension feeders, using their numerous fine teeth to filter small organisms from shallow water.Pterodaustro was adapted forflamingo-like filter-feeding.[182]
In contrast,Azhdarchoidea mostly were terrestrial pterosaurs.Tapejaridae were arboreal omnivores, supplementing seeds and fruits with small insects and vertebrates.[171][183]Dsungaripteridae were specialist molluscivores, using their powerful jaws to crush the shells of molluscs and crustaceans.Thalassodromidae were likely terrestrial carnivores.Thalassodromeus itself was named after a fishing method known as "skim-feeding", later understood to be biomechanically impossible. Perhaps it pursued relatively large prey, in view of its reinforced jaw joints and relatively high bite force.[184]Azhdarchidae are now understood to be terrestrial predators akin to groundhornbills or somestorks, eating any prey item they could swallow whole.[185]Hatzegopteryx was a robustly built predator of relatively large prey, including medium-sized dinosaurs.[186][187]Alanqa may have been a specialist molluscivore.[188]
A 2021 study reconstructed the adductor musculature of skulls frompterodactyloids, estimating the bite force and potential dietary habits of nine selected species.[189] The study corroborated the view ofpteranodontids,nyctosaurids andanhanuerids aspiscivores based on them being relatively weak but fast biters, and suggest thatTropeognathus mesembrinus was specialised in consuming relatively large prey compared toAnhanguera.Dsungaripterus was corroborated as adurophage, withThalassodromeus proposed to share this feeding habit based on high estimatedbite force quotients (BFQ) and absolute bite force values.[189]Tapejara wellnhoferi was corroborated as a specialised consumer of hard plant material with a relatively high BFQ and high mechanical advantage, andCaupedactylus ybaka andTupuxuara leonardii were proposed to be ground-feeding generalists with intermediate bite force values and less specialised jaws.[189]
Pterosaurs are known to have been eaten bytheropods. In the 1 July 2004 edition ofNature, paleontologistÉric Buffetaut discusses an Early Cretaceous fossil of three cervicalvertebrae of a pterosaur with the broken tooth of aspinosaur, most likelyIrritator, embedded in it. The vertebrae are known not to have been eaten and exposed to digestion, as the joints are still articulated.[190] Fossils ofPteranodon have been found with tooth marks from sharks such asSqualicorax,[191] and a fossil with tooth marks from theToolebuc formation has been interpreted as being attacked or scavenged by anichthyosaur (most likelyPlatypterygius).
Fossilpterodactyloid juvenile from the Solnhofen Limestone
While very little is known about pterosaur reproduction, it is believed that, similar to all dinosaurs, all pterosaurs reproduced by laying eggs, though such findings are very rare. The first known pterosaur eggs were found in the quarries of Liaoning, the same place that yielded feathered dinosaurs, and in Loma del Pterodaustro (Lagarcito Formation,Argentina). The eggs fromLiaoning were squashed flat with no signs of cracking, so evidently the eggs had leathery shells, as in modern lizards.[192] The egg from theLagarcito Formation was laid by aPterodaustro,[193][194] a pterosaur known by abundant material.[195] This was supported by the description of an additional pterosaur egg belonging to the genusDarwinopterus, described in 2011, which also had a leathery shell and, also like modern reptiles but unlike birds, was fairly small compared to the size of the mother.[196] In 2014 five unflattened eggs from the speciesHamipterus tianshanensis were found in an Early Cretaceous deposit in northwest China. Examination of the shells by scanning electron microscopy showed the presence of a thin calcareous eggshell layer with a membrane underneath.[197] A study of pterosaur eggshell structure and chemistry published in 2007 indicated that it is likely pterosaurs buried their eggs, like moderncrocodiles andturtles. Egg-burying would have been beneficial to the early evolution of pterosaurs, as it allows for more weight-reducing adaptations, but this method of reproduction would also have put limits on the variety of environments pterosaurs could live in and may have disadvantaged them when they began to face ecological competition frombirds.[198]
ADarwinopterus specimen showcases that at least some pterosaurs had a pair of functionalovaries, as opposed to the single functional ovary in birds, dismissing the reduction of functional ovaries as a requirement for powered flight.[199]
Growth series ofRhamphorhynchus specimens showing changes throughout life
Wing membranes preserved in pterosaur embryos are well developed, suggesting that pterosaurs were ready to fly soon after birth.[200] However,tomography scans of fossilisedHamipterus eggs suggests that the young pterosaurs had well-developed thigh bones for walking, but weak chests for flight.[201] It is unknown if this holds true for other pterosaurs. Fossils of pterosaurs only a few days to a week old (called "flaplings") have been found, representing several pterosaur families, including pterodactylids, rhamphorhinchids, ctenochasmatids and azhdarchids.[25] All preserve bones that show a relatively high degree of hardening (ossification) for their age, and wing proportions similar to adults. In fact, many pterosaur flaplings have been considered adults and placed in separate species in the past. Additionally, flaplings are normally found in the same sediments as adults and juveniles of the same species, such as thePterodactylus andRhamphorhynchus flaplings found in theSolnhofen limestone of Germany, andPterodaustro flaplings from Argentina. All are found in deep aquatic environment far from shore.[202]
Some pterosaurs may have reproduced incolonies similar to those of modern seabirds
For the majority of pterosaur species, it is not known whether they practiced any form of parental care, but their ability to fly as soon as they emerged from the egg and the numerous flaplings found in environments far from nests and alongside adults has led most researchers, including Christopher Bennett and David Unwin, to conclude that the young were dependent on their parents for a relatively short period of time, during a period of rapid growth while the wings grew long enough to fly, and then left the nest to fend for themselves, possibly within days of hatching.[25][203] Alternatively, they may have used stored yolk products for nourishment during their first few days of life, as in modern reptiles, rather than depend on parents for food.[202] FossilisedHamipterus nests were shown preserving many male and female pterosaurs together with their eggs in a manner to a similar to that of modernseabirdcolonies.[197][204] Due to how underdeveloped the chests of the hatchlings were for flying, it was suggested thatHamipterus may have practiced some form of parental care.[201] However, this study has since been criticised.[205] Most evidence currently leans towards pterosaur hatchlings beingsuperprecocial, similar to that ofmegapode birds, which fly after hatching without the need of parental care. A further study compares evidence for superprecociality and "late term flight" and overwhelmingly suggests that most if not all pterosaurs were capable of flight soon after hatching.[206] A later study suggested that while smaller-bodied pterosaurs were most likely superprecocial or precocial, owing to the consistent or decreasing wing aspect ratio during growth, certain large-bodied pterosaurs, such asPteranodon showed possible evidence of their young beingaltricial, due to the fast rate the limb bones closest to the body grew compared to any other element of their skeleton after hatching. Other factors mentioned were the limits of soft shelled eggs and the size of the pelvic opening of large female pterosaurs.[207][208]
Growth rates of pterosaurs once they hatched varied across different groups. In more primitive, long-tailed pterosaurs ("rhamphorhynchoids"), such asRhamphorhynchus, the average growth rate during the first year of life was 130% to 173%, slightly faster than the growth rate ofalligators. Growth in these species slowed after sexual maturity, and it would have taken more than three years forRhamphorhynchus to attain maximum size.[203] In contrast, the more advanced, largepterodactyloid pterosaurs, such asPteranodon, grew to adult size within the first year of life. Additionally, pterodactyloids haddeterminate growth, meaning that the animals reached a fixed maximum adult size and stopped growing.[202]
A 2021 study indicates that pterosaur juveniles of larger species increasingly took the roles previously occupied by adult small pterosaurs.[149]
Comparisons between thescleral rings of pterosaurs and modern birds and reptiles have been used to infer daily activity patterns of pterosaurs. The pterosaur generaPterodactylus,Scaphognathus, andTupuxuara have been inferred to bediurnal,Ctenochasma,Pterodaustro, andRhamphorhynchus have been inferred to benocturnal, andTapejara has been inferred to becathemeral, being active throughout the day for short intervals. As a result, the possibly fish-eatingCtenochasma andRhamphorhynchus may have had similar activity patterns to modern nocturnal seabirds, and the filter-feedingPterodaustro may have had similar activity patterns to modernanseriform birds that feed at night. The differences between activity patterns of theSolnhofen pterosaursCtenochasma,Rhamphorhynchus,Scaphognathus, andPterodactylus may also indicateniche partitioning between these genera.[209]
Quetzalcoatlus models inSouth Bank, created by Mark Witton for the Royal Society's 350th anniversary
Pterosaurs have been a staple of popular culture for as long as their cousins the dinosaurs, though they are usually not featured as prominently in films, literature or other art. While the depiction of dinosaurs in popular media has changed radically in response to advances in paleontology, a mainly outdated picture of pterosaurs has persisted since the mid-20th century.[210]
The vague generic term "pterodactyl" is often used for these creatures. The animals depicted in fiction and pop culture frequently represent either thePteranodon or (non-pterodactyloid)Rhamphorhynchus, or a fictionalized hybrid of the two.[210] Many children's toys and cartoons feature "pterodactyls" withPteranodon-like crests and long,Rhamphorhynchus-like tails and teeth, a combination that never existed in nature. However, at least one pterosaurdid have both thePteranodon-like crest and teeth:Ludodactylus, whose name means "toy finger" for its resemblance to old, inaccurate children's toys.[211] Pterosaurs have sometimes been incorrectly identified as (the ancestors of)birds, though birds aretheropod dinosaurs and not descendants of pterosaurs.
Pterosaurs were used in fiction in Sir Arthur Conan Doyle's 1912 novelThe Lost World and its1925 film adaptation. They appeared in a number of films and television programs since, including the 1933 filmKing Kong, and 1966'sOne Million Years B.C. In the latter, animatorRay Harryhausen had to add inaccurate bat-like wing fingers to his stop motion models in order to keep the membranes from falling apart, though this particular error was common in art even before the film was made.Rodan, a fictional giant monster (orkaiju) which first appeared in the 1956 filmRodan, is portrayed as an enormous irradiated species ofPteranodon.[212][213] Rodan has appeared in multiple JapaneseGodzilla films released during the 1960s, 1970s, 1990s, and 2000s, and also appeared in the 2019 American-produced filmGodzilla: King of the Monsters.[213][214][215]
Versperopterylus is one of the only pterosaurs with grasping feet, despite popular depictions of them on many pterosaurs
After the 1960s, pterosaurs remained mostly absent from notable American film appearances until 2001'sJurassic Park III. Paleontologist Dave Hone noted that the pterosaurs in this film had not been significantly updated to reflect modern research. Errors persisting were teeth while toothlessPteranodon was intended to be depicted, nesting behavior that was known to be inaccurate by 2001, and leathery wings, rather than the taut membranes of muscle fiber required for pterosaur flight.[210] Petrie fromThe Land Before Time (1988), is a notable example from an animated film.[216]
In most media appearances, pterosaurs are depicted aspiscivores, not reflecting their full dietary variation. They are also often shown as aerial predators similar tobirds of prey, grasping human victims with talons on their feet. However, only the smallanurognathidVesperopterylus and smallwukongopteridKunpengopterus[217] are known to possess prehensile feet and hands respectively; all other known pterosaurs have flat, plantigrade feet with no opposable toes, and the feet are generally proportionally small, at least in the case of the Pteranodontia.[16]
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