Pterodactyls are , an order of extinct flying reptiles technically known as Pterosauria. They lived exclusively during the Mesozoic period, from the beginning of the Jurassic to near the close of the Cretaceous. Their fossil remains have been found in Europe and North America, but are best known from the chalk deposits of western Kansas, where many hundred specimens have been collected. Of known reptiles they are nearest allied to the dinosaurs; they are only distantly related to birds. They are especially characterized by their very hollow bones and the extraordinary elongation of the fourth (according to some authors, the fifth) finger, which supported a thin bat-like membrane that extended to the sides of the body and the legs. Not only were the bones very hollow, more so than in any living birds, but they were composed of very dense osseous tissue and were pneumatic, that is, had openings, usually near the ends, for the ingress and egress of air, as in birds. The nature and extent of the wing membrane, or patagium, are known from impressions in the rocks, but the covering of the body elsewhere is still in doubt. That the body was not clothed with feathers is certain, but it may have had, like that of most reptiles, horny scales.
The neck was more or less elongated and very flexible; the legs were
relatively feeble and of but little use in locomotion upon land; the
breastbone, which is poorly developed in other reptiles and wholly
absent in early reptiles, was of great size, covering the whole under
side of the thorax. Unlike birds, however, it had no real keel but only
a stout projection in front for the attachment of muscles. The pelvic
or hip bones were well developed for the support of the hind legs,
which were of material use in flight. The fifth finger was absent; the
first three fingers were short and useful only for clinging to rocks
In all the early kinds, those from the Jurassic, the skull, of moderate length, was provided with long and sharp teeth. The tail was long and flexible and had at its extremity a diamond-shaped expansion for use in controlling flight. The bones of the skeleton were less hollow and the wing was proportionally less elongated. The first bone of the wing-finger, that is, its metacarpal, was relatively short, never longer than the forearm, and the first three fingers were articulated directly with the wrist. There were five separate toes and the feet were of some use upon land. None was of large size, not exceeding five or six feet in expanse. The best known form is Rhamphorhynchus, and the group or suborder is known as the Pterodermata.
The later and much more specialized group, beginning near the close of the Jurassic, known as the Pterodactyloidea, had the skull more elongated, the wing-finger longer, with its metacarpal longer than the forearm, the first three fingers of the hand loosely attached in the flesh, the tail vestigial, the pelvis larger and firmer and the feet with only four toes. The earliest of these, of which Pterodactylus is the best known example, were small, some with a body not larger than that of a sparrow, and they had teeth in the jaws. The later ones, however, those from the Upper Cretaceous, of which so many are found in America, reached a size of more than 20 feet from tip to tip of wings. The skull was very long and slender, in some with an enormously developed crest upon the back of the head, and the jaws were without teeth. The neck was longer and more flexible, in many with additional articulations, giving greater strength; the bones of the shoulder were united into a firmly ossified ring, which, unlike all other known animals, articulated directly with the spinal column; the wrist was firmer; the wing-finger still more elongated ; the small bone of the legs had disappeared, as in birds; and the first bone of the ankle, the astragalus, had become indistinguishably united with the leg bone, as in birds. The most noted member of this group is Pteranodon.
In their maximum and final development the Pterodactyls attained the highest volant powers of all creatues, whether of the past or present, being quite incapable of locomotion except in the air Pteranodon, with a wing expanse of 22 or more feet, had a body smaller than that of a turkey. Nyctosaurus, an allied genus from Kansas, with a body only six inches long and five or six inches across the shoulders, measured eight feet from tip to tip of expanded fingers, and probably did not weigh more than five pounds when alive. They doubtless spent most of their time in the air, resting suspended from cliffs by their small clawed fingers, much like the way of bats, except that their fingers, instead of their toes, are used for suspension. The presence of bony plates in the sclerotic membranes of the eyes indicates either nocturnal or soaring habits.
In flight, unlike birds and bats, their "wings" served more as gliding surfaces, and could have been used only for upward and downward motion. Flight was controlled by the legs, which were extended backward and connected by membrane, serving the purpose of the feathered tail in birds. The rudder-tailed Rhamphorhynchus was a veritable monoplane.
Their food habits are only imperfectly known. Because so many of their remains are found in ocean deposits, it is believed that they fed largely upon fishes, and this assumption is strengthened by the discovery, in several instances, of the remains of their stomach contents containing comminuted fishbones. But it is probable that they also lived in part upon other flying creatures, insects and small birds, which must have been swallowed whole. Their brain was better developed than in other reptiles, and because of this and of the highly-developed, pneumatic skeleton, it has been thought by some that they were warm blooded; they have even been placed in a separate class of backboned animals. They were, however, true reptiles, even though warm blooded, which may have been possible.
Remains of young Pterodactyls have never been found. Like most reptiles they were probably oviparous, since otherwise, among the many hundreds of known specimens, embryonic young would probably have been found. The bones of the pelvis, unlike those of birds, were closely connected, and only eggs of small size could have passed through it, not much larger than hens' eggs, even in the largest kinds. Such small young would have been practically helpless, which, together with the greater intelligence of the adult animals, as indicated by their large brains, renders it probable that the young were cared for by the parents until able to care for themselves. These facts suggest limited breeding grounds, and extensive seasonal migration.
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