PTERODACTYL, a term familiarly used for any member of the order Pterosauria, or winged reptiles. The pterodactyls are extinct flying reptiles found in rocks of all ages from the Lower Lias or perhaps the Rhaetic to the Upper Cretaceous. They fall into two great groups distinguished from one another by the presence of a long tail with a horizontal fin at its tip, in the one, and the lack of a tail in the other.
The best known form is Rhamphorynchus from the Solenhofen slate of Bavaria and probably the Kimmeridge clay of England. Rhamphorynchus has a head about 31 in. long, with a mouth open ing very widely and armed with long, slender, sharp-pointed teeth. The eye, which is placed above the articulation of the lower jaw, is very large, and like that of many birds has a series of bony plates lying in its wall. The paired nostrils lie far back in front of the eyes. The neck, which is some 2 in. long, was flexible, and the head was carried at right angles to the neck. The body is small, about 4 in. in length by 14 in. in diameter. The tail is enormously long (15 in.) and although built of many joints, is stiffened by ossified tendons so that it must have moved as a whole. The wings are stretched membranes made by folds of skin held out by the greatly elongated fore-limb, and especially by the enormously extended fourth finger, the width across the wings when fully spread is some 25 inches. The bony finger lies practically at the for ward edge of the wing, the membrane which forms the rest of the structure being only some 2 in. from front to back, and passing backwards along the side of the body to the hind leg. The extrem ity of the tail bears a horizontal flap of membrane. The three first fingers of the hand are free and provided with large claws ; they stand out in front of the wings and must have been used for holding food or for help in landing. The knees included in the
wing membrane stand straight out from the side of the body, the lower leg is long and there are five slender toes, the first being always curiously bent inwards and downwards. The other f our toes seem to have been connected by a web.
Rhamphorynchus was covered with a smooth skin usually without scales, but the top of the head bore a tuft of hair-like protuberances. The animal ap pears to have lived like a sea-gull on fish, and it is exceedingly diffi cult to understand how it could ever have risen from land or water after alighting.
The group of tail-less ptero dactyls is best represented by Pteranodon from the Kansas chalk. This creature had a wing-spread of 18 ft. and its head (measured from the tip of the snout to the summit of a great crest which rises from the occiput) is nearly 4 ft. in length. It was perhaps the largest flying animal of which we have any knowledge. Despite its great size it was extremely light, the wing-bones consisting of a bony layer no thicker than a visiting card, surround ing an air space which might be more than an inch in diameter; even the bone of an albatross is a crude and heavy structure in comparison. The remains of these giant animals are found in the Kansas and English chalk sufficiently commonly to show that they flew at a distance of some hundreds of miles from land. The brain of these large pterodactyls is extraordinarily like that of a bird, and its char acters are such as to suggest that they practically lacked a sense of smell and depended on sight for the capture of their food.
See REPTILES. (D.M.S.W.)