Pterodactyl (pterodactylus, Cuv.; Gr.Pterodactyl 140023 , wing, and Pterodactyl 140024 , finger), a genus of fossil flying reptiles, possessing essentially the characters of saurians, with some only apparent relations to bats and birds. They have been divided into three genera according to the number of joints in the wing-bearing finger and the disposition of the teeth; all are characteristic of the secondary epoch, being found principally in the lithographic schists of So-lenhofen, and in the oolite, lias, wealden, and chalk of Europe and the United States. In the genus pterodactylus the jaws had teeth even to the extremity; the skull was elongated, with the intermaxillaries large; nasal opening wide and near the middle of the muzzle, partly closed in front by a small bone as in the monitors, and with a surrounding circle of small bones and a small opening into the orbit as in birds; the lower jaw, as in crocodiles, had no coronary process, and was articulated behind the eyes; the teeth, 5 to 17 on each side, were conical, slightly arched, compressed, inserted in separate cavities, and hollowed at the base; neck of 7 stout vertebrae; dorsals 13 to 15, and, with the ribs, weak; lumbar 2 or 3, sacral 6, anchylosed together, and caudal 10 to 15; the shoulder blade and coracoid bone separate and weak; scapular arch and pelvis as in lizards, except that the last seems to have had marsupial bones, according to Pictet; the long bones hollow and with air openings, as in birds; humerus short and stout, and forearm twice as long; hind limbs slender, with 5 moderate toes of the same length; 5 or 6 bones in the wrist, 5 metacarpals, 5 fingers, with respectively 1, 2, 3, 4, and 4 joints; the first 4 short and with hooked nails, the external very long, equal to the neck and body, and nailless; the gape of mouth very large.

This singular animal was referred to the swimming birds by Blumen-bach and to the bats by Sömmering, and was determined to be a reptile by Cuvier. The nearly equal and conical teeth, very small cranial cavity, different number of joints in the fingers, and reptilian shape of sternum and scapula show that it was not a bat-like mammal; the existence of teeth, the small number of the vertebrae in the neck, the thinness of the ribs and tail and the absence of recurrent processes in the latter, the form of the sternum and number of the fingers, prove that it was not a bird. These characters place it among reptiles, but it had also a modification of the anterior extremities in the form of wings, which are not possessed by any existing or any other fossil members of the class, the so-called wings of the dragon being merely membranous expansions from the sides of the body supported by the ribs. The form of the wings is also remarkable and unique; in birds the fingers are very little separated, and serve as a basis for the plumes; in bats the flying membrane is stretched upon the four elongated fingers, the thumb remaining rudimentary; but in the pterodactyl the external finger alone is greatly developed and supports the flying membrane, the other four having the usual short dimensions; the membrane extended probably from the long finger along the sides of the body to the hind limbs and beyond, including the tail.

About 20 species are described, varying in alar extent from a few inches to four or five yards; they probably flew and crept about in the manner of bats; the form of the teeth and strength of the jaws indicate a carnivorous animal, but of feeble powers; the smaller species must have been insectivorous, and the largest may have seized fish or small reptiles of their own or other genera. The great size of the eyes indicates nocturnal habits; the posterior limbs were so far developed that they could doubtless assume an erect position like birds, and perch on trees; the claws of the fore and hind feet would also enable them to climb along the rocks; the body was probably scaly, as in lizards. From the weakness of the scapular arch some have doubted the power of active flight in the pterodactyl, believing that the wing membranes could only support it in the air when leaping, in a little more perfect manner than in the dragons; but it must be remembered that the atmosphere of the secondary geological age was much more dense than the present, requiring proportionally less muscular force for aërial locomotion. The most anciently known species is the P. longirostris (Oken), about the size of a woodcock, with a length of 10 in. and an alar extent of 21 in.; the teeth were 1/1 1/7 on each side.

The P. brevirostris (Cuv.) had a shorter muzzle, the head resembling more that of a goose just hatched than of a reptile; the teeth were very small, 5/8; the total length was less than 3 in., and there were only four posterior toes. Other species were less than 2 in. long, while on the contrary the P. ornis (Giebel) of the wealden was 2 ft. in length; in the chalk of Maidstone, England, Mr. Bowerbank detected bones of a species which he named P. giganteus, 6 to 7 ft. in alar extent; the P. Cuvieri (Bowerb.) is believed to have spread 16 1/2 ft. In 1871 Prof. Marsh found in the upper cretaceous rocks of western Kansas a species with an expanse of wing of 20 ft., which he named P. Owenii. Since 1869 Prof. Marsh has discovered the remains of three different species in the same regions. - The genus rhamphorhynchus (H. von Meyer) or ornithocephalus (Sömm.) was separated for a few species of the Jurassic age, having the anterior portion of the jaws without teeth, and probably with a horny beak; the scapula and coracoid were consolidated together, and the tail long and stiff, with about 30 vertebrae; there were four joints in the wing finger; the largest species was about 18 in. long.

The genus ornithopterus (H. von Meyer) had only two joints in the wing finger.