PTERODACTYL, t ( Neo-Lat., from Gk. 7r-rEp6p, ',knot. feather, wing + ocittrvXos, dekty(os, finger). The common name for any one of the living lizards. remains of which are found in the Mesozoic rocks. There are about twenty different genera of pterodactyls. all in eluded in the order Pterosauria (wing-lizards), stretched along the sides of the body and sup ported by the fore and hind limbs and the tail. The structure of the fore limb is quite different, however, from that seen in bats and birds, and presents equally interesting modifications of the parts of the arm in the adaptation of the latter from a walking leg to a wing-like organ. The long bones are considerably lengthened, the first finger is sometimes represented by a sort of dew claw, the second. third, and fourth fingers are small and slender and furnished with sharp hooked claws, and the fifth, or `little finger,' is greatly elongated and strengthened to form the framework along which the anterior edge of the wing membrane is attached. Impressions of these also called Ornithosauria (bird-lizards). All the members of this order show a remarkable adapta tion of the lizard body to bird-like habits, though in structure they remain essentially rep tilian. They cannot be considered as ancestral to the birds, for they constitute a wholly inde pendent line of descent, probably derived from common dinosaurian ancestors. and they present an instructive example of parallelism of evolu tion due to adoption by two separate races of similar modes of life. The pterodactyls have skeletons of light hut firm construction with hollow bones. The earl ier forms had strong, spreading teeth which gradually disappeared in successively later mem bers of the group. and the loss of the teeth was accompanied by a corre sponding increase in length and sharpness of the jaws until in the latest genera (Pteranodon. etc.) the jaws are dagger-like. The large eyes, surrounded by a ring of sclerotic plates, are placed well back and on the sides of the skull. The body
was short and rather stout, the limbs lowg and slender, and in the earlier forms there was a long slender tail. The wings resembled in gen eral those of the bats rather than those of birds, for they consisted of thin but strong membranes wing membranes have in sev eral eases been found so well preserved that the courses of the arteries are easily traceable. The hind limbs are of decidedly reptilian structure and from veloped organs of locomotion in the earlier members of the group, they degenerated to weak clawed organs of prehension by which the later, more highly special ized, pterodactyls probably suspended themselves from points of rocks or from the limbs of trees after the manner of the modern bats.
The various genera range in size from less than 12 inches to about 20 feet in spread of wings. Some of them were evidently able to do little more than sail on leaping through the air. as does the flying squirrel, by means of the stretched membranes; while others were among the most powerful flying creatures that have ever lived. The principal genera are Dimorphodon. Rham phorbynchus, Pterodaetylus, and Pteranodon, or Ornithostoma.
BIBLIOGRAPHY. Von Zittel and Eastman. TextBibliography. Von Zittel and Eastman. Text- Book of Pahrontology, vol. ii. (New York and London, 1902) : Woodward, Outlines of Verte brate Palo-ontology for Students of Zohlogy (Cambridge, 1898) Seeley, The Ornithoseuria 1890) ; id.. Dragons of the Air (London, 1901) ; Zittel. "Die Flfigsaurier aus dent Litho graphischen Schiefer," Pakeontogrephice, vol. xxix. (Berlin, 18S2) ; Williston. "Winged Rep tiles." Popular Science Monthly, vol. lx. (New York, 1902) : Lucas. "The Greatest Flying Crea ture, the Great. Pterodactyl. Ornithostoma." A nmial Report of the Smithsonian Institution for 1901 (Washington. 1902).