Pterosaur
Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous. Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger.
Traditionally, pterosaurs were divided into two major types. Basal pterosaurs were smaller animals, up to two meter wingspan, with fully toothed jaws and, typically, long tails. Their wide wing membranes probably included and connected the hindlimbs. On the ground, they would have had an awkward sprawling posture due to short metacarpals, but the anatomy of their joints and strong claws would have made them effective climbers, and some may have lived in trees. Basal pterosaurs were insectivores, piscivores or predators of small land vertebrates. Later pterosaurs evolved many sizes, shapes, and lifestyles. Pterodactyloids had narrower wings with free hindlimbs, highly reduced tails, and long necks with large heads. On the ground, they walked well on all four limbs due to long metacarpals with an upright posture, standing plantigrade on the hind feet and folding the wing finger upward to walk on the metacarpals with the three smaller fingers of the hand pointing to the rear. They could take off from the ground, and fossil trackways show that at least some species were able to run, wade, and/or swim. Their jaws had horny beaks, and some groups lacked teeth. Some groups developed elaborate head crests with sexual dimorphism. Since 2010 it is understood that many species, the basal Monofenestrata, were intermediate in build, combining an advanced long skull with long tails.
Pterosaurs sported coats of hair-like filaments known as pycnofibers, which covered their bodies and parts of their wings. Pycnofibers grew in several forms, from simple filaments to branching down feathers. These may be homologous to the down feathers found on both avian and some non-avian dinosaurs, suggesting that early feathers evolved in the common ancestor of pterosaurs and dinosaurs, possibly as insulation. They were warm-blooded, active animals. The respiratory system had efficient unidirectional "flow-through" breathing using air sacs, which hollowed out their bones to an extreme extent. Pterosaurs spanned a wide range of adult sizes, from the very small anurognathids to the largest known flying creatures, including Quetzalcoatlus and Hatzegopteryx, which reached wingspans of at least nine metres. The combination of endothermy, 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 the last common ancestor of the Saurischia and Ornithischia, which excludes the pterosaurs. 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 as pterodactyls, particularly in fiction and journalism. However, technically, pterodactyl may refer to members of the genus Pterodactylus, and more broadly to members of the suborder Pterodactyloidea of the pterosaurs.
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 by eggs, some fossils of which have been discovered.
Anatomy
The anatomy of pterosaurs was highly modified from their reptilian ancestors by the adaptation to flight. Pterosaur bones were hollow and air-filled, like those of birds. 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. Pterosaur skeletons often show considerable fusion. In the skull, the sutures 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 shoulder blade. Likewise, the sacral vertebrae could form a single synsacrum while the pelvic bones fused also.Size
Pterosaurs were highly diverse in size, and some were the largest flying organisms in earth's history. Early pterosaurs of the Triassic and Jurassic periods were typically small animals with wingspans only up to, while most Cretaceous pterosaurs were larger. Some isolated specimens indicate exceptions to this rule, and the divisions of size across time may be a partial result of an incomplete fossil record. Anurognathids may have been the smallest pterosaurs, with wingspans of as small as, though the age of these individuals remains uncertain. The largest pterosaurs were members of Azhdarchidae such as Hatzegopteryx and Quetzalcoatlus, which could attain estimated wingspans of and weights of.Skull
Pterosaurs have large skulls compared to other flying vertebrates, the birds and bats. Later pterosaurs had very elongated skulls, sometimes longer than the whole torso. Many bones were fused in adults. The skulls were pierced by multiple large holes: the bony nostrils, eye sockets, the antorbital fenestrae in the snout side and two temporal fenestrae on each rear side. Monofenestratan pterosaurs fused the nasal and antorbital fenestra into a single large nasantorbital fenestra. The back of the head was at first vertical in orientation, but rotated to nearly horizontal later in evolution of some groups. The paired lower jaws were fused at the front into an elongated mandibular symphysis. The lower jaws of the earliest pterosaurs were pierced at the rear by a mandibular fenestra, but this was lost in later species.The snout or the back of the skull often sported an upward projecting crest, sometimes of enormous size. The lower jaws could likewise feature a downward projecting keel. These crests could be expanded in size and shape with soft tissues. Some crests entirely lacked a bone core, with their presence only known from exceptionally well preserved specimens.
Early pterosaurs were heterodont, with multiple tooth types. Later pterosaurs were homodont, having a single tooth form, often elongated and conical, throughout the skull. The teeth were replaced continuously throughout life. Between species, the dentition varied considerably. Fish eaters often had longer teeth in an expansion of the jaw tips. Filter feeders could have a sieve of up to a thousand teeth. Some later pterosaur groups were entirely toothless, featuring a horny beak similar to that of birds. Most species had some keratinized beak tissue, though never in the same snout section as the teeth.
Neck and torso
The vertebral column of pterosaurs had up to seventy vertebrae. Later pterosaurs have unique structures at the sides of the vertebrae, called exapophyses, and the concave fronts may possess a midline prong, the hypapophysis. Pterosaur necks were typically long, deep, and straight, and in pterodactyloids was longer than the torso. The number of neck vertebrae is always seven, or nine if one includes two trunk vertebrae. Pterodactyloids have lost all neck ribs. The neck was deep and well-muscled.The torso was short and compact. Up to seven front back vertebrae and ribs can be fused into a rigid structure known as a notarium.
The shoulder girdle was strong and well-muscled, with the upper shoulder blade and connected lower coracoid fused in later species into a single scapulocoracoid. The top of this structure fitted to the notarium, while the lower end connected to the breastbone, forming a rigid closed loop, better to withstand the forces of flapping flight. The shoulder joint was saddle-shaped allowing considerable movement to the wing. It faced obliquely sideways and upwards.
The breastbone was wide with a shallow keel, via sternal ribs attached to the dorsal ribs. Behind it, belly ribs covered the entire belly. To the front, a long pointy structure termed the cristospina jutted obliquely upwards. The thorax was deepest at the rear of the breastbone. There were no clavicles.
The pelvis of pterosaurs was of moderate size compared to the body as a whole. Often the three pelvic bones were fused. The sacrum had up to ten sacral vertebrae, sometimes connected by a bar in a similar fashion to the notarium. The 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. Then, 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. It was directed obliquely upwards, preventing a perfectly vertical position of the leg. 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.
Wings
Wing membranes
The primary wing membranes attached to the extremely long fourth fingers, probably extending to the ankles. The profile of the trailing edge is uncertain. The membranes were not leathery flaps composed of skin but highly complex dynamic structures suited to serve an active flight style. They were strengthened by closely spaced fibers called actinofibrils, in three distinct layers in the wing, in a crisscross pattern superimposed on one another. They had a stiffening or strengthening function. Also a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels was present. This combination may have allowed the animal to adjust the wing slackness and camber to control lift.File:Pterosaur wing surfaces.png|thumb|Two pterosaurs in dorsal view, with wing parts labeled
The wing membrane is divided into three parts. The propatagium, was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight. The brachiopatagium stretched from the fourth finger to the hindlimb. Finally, a membrane that stretched between the legs, possibly incorporated the tail, called the uropatagium. It might only have connected the legs, rendering it a cruropatagium. Early pterosaurs perhaps had a broader uro/cruropatagium stretching between their long fifth toes; pterodactyloids, lacking such toes, only had membranes running along the legs. Fossils of the rhamphorhynchoid Sordes, the anurognathid Jeholopterus, suggest that the wing membrane did attach to the hindlimbs. However, pterosaur limb proportions show that there was considerable variation in wing-plans.