9th Edition of Encyclopedia Britannica - free ninth edition online encyclopedia Britannica » Volume 20 [PRU - ROS]: Acute Rheumatism to Redruth


jaws pterodactyles teeth genera digit

PTERODACTYLE. The extinct flying reptiles known as " pterodactyles " are among the most aberrant forms of animals, either living or extinct. Since the beginning of this century, when Blumenbach and Cuvier first described the remains of these curious creatures, they have occupied the attention of naturalists, and various opinions have been expressed as to their natural affinities. The general proportions of their bodies (excepting the larger head and neck) and the modification of the forelimb, to support a membrane for flight, remind one strongly of the bats, but the resemblance is only superficial ; a closer inspection shows that their affinities are rather with reptiles and birds.

In all pterodactyles the head, neck, and forelimb are large in proportion to the other parts of the body (fig. 1). The skull is remarkably avian, and even the teeth, which PTERODACTYLE 26 most of them possess, and which seem so unbird-like, are paralleled in the Cretaceous toothed birds of North America. Judging from the form of the skull, the brain was small, but rounded and more like that of a bird than that of a reptile. The position of the occipital condyle, beneath and not at the back of the skull, is another character pointing in the same direction. The nasal opening is not far in advance of the large orbit, and in some forms there is a lachrymo-nasal fossa between them. The pre-maxillae are large, while the maxilla are slender. In certain species the extremities of the upper and lower jaws seem to have been covered with horn, and some forms at least had bony plates around the eye. The union of the post-frontal bone with the squamosal to form a supra-temporal fossa is a reptilian character. Both jaws are usually provided with long slender teeth, but they are not always present. The vertebral column may be divided into cervical, dorsal, sacral, and caudal regions. The centra of the vertebra are proccelous, - that is, the front of each centrum is cup-like and receives the ball-like hinder extremity of the vertebra next in front of it. The eight or nine cervical vertebrae are always large, and are succeeded by about fourteen or sixteen which bear ribs. Probably there are no vertebra which can be called lumbar. The sacrum consists of from three to six vertebra. The tail is short in some genera and very long in others. The sternum has a distinct median crest, and the scapula and coracoid are also much like those of carinate birds. The humerus has a strong ridge for the attachment of the pectoral muscle, and the radius and ulna are separate bones. There are four distinct metacarpals ; passing from the inner or radial side, the first three of these bear respectively two, three, and four phalanges, the terminal ones having had claws. The phalanges of the outermost digit are much elongated, and except in one doubtful form are always four in number. It is the extreme elongation of this outer digit, for the support of the patagium, which is the most characteristic feature of the pterodactyle's organization. A slender bone called the " pteroid " is sometimes seen extending from the carpal region in the direction of the upper part of the humerus. Some naturalists look upon the pteroid merely as an ossification of a tendon, corresponding with one which is found in this position in birds, while others are inclined to regard it rather as a rudiment ary first digit, modified to support the edge of the patagium. The pelvis is small. In form the ilia resemble rather the ornithic than the reptilian type ; but the other portions of the pelvis are more like those of the crocodiles. The hind' pectoral muscles and a corresponding strength in the arms. The form of the forelimb, especially its outer digit, indicates in no uncertain • manner that it supported a flying membrane; but within the last few years this has been (fig. 2): The occurrence of pterodactyle remains in marine deposits would seem to indicate that they frequented the seashore ; and it is tolerably certain that those forms with long and slender teeth were, in part at least, fish-eaters. Seeing, however, that the armature of the jaws varies considerably in the different genera, it is most likely that their diet varied accordingly.

Pterodactyles present so many avian peculiarities that it has been proposed to place them in a special group, to be called Ornithosauria, which would hold a position intermediate between Aves and .Reptilia. On the other hand, pterodactyles are thought by most authorities to have a closer relationship with the reptiles, and the different genera are placed in a separate order of the Reptilia called Pterosauria. The most important genera are five. (1) Pterodactylus ; these have the jaws pointed and toothed to their extremities, and the tail very short. (2) Rharnphorhynchus (fig. 2); this genus has the jaws provided with slender teeth, but the extremities of both mandible and upper jaw are produced into toothless beaks, which were probably covered with horn ; the tail is extremely long. (3) Dimorphodon ; in this form the anterior teeth in both upper and lower j jaws are long, but those at the hinder part of the jaws are short ; the tail is extremely long. (4) Pteranodon ; similar in most respects to Pterodactylus, but the jaws are devoid of teeth. In these four genera the outer digit of the manes has four phalanges. (5) Ornithopterus; this form is said to have only two phalanges in the outer digit of the manus ; the genus, however, is very imperfectly known, and it has been suggested that it may perhaps be a true bird.

The Pterosauria are only known to have lived during the Mesozoic period. They are first met with in the Lower Lias, the Dimorphodon macronyx from Lyme Regis being perhaps the earliest known species. The Jurassic slates of Solenhofen have yielded a large number of beautifully preserved examples of Pterodactylus and Rhamphorhynchus, and remains of the same genera have been found in England in the Stonesfield slate. Bones of pterodactyles have also been obtained in some abundance from the Cretaceous phosphatic deposits near Cambridge ; and their remains have been met with occasionally in the Wealden and Chalk of Kent. The germs Pteranodon is only known from the Upper Cretaceous rocks of North America. The Pterosauria were for the most part of moderate or small size (see fig. 1), but some attained to very considerable dimensions ; for instance, Rhamphorhynchus Bucklandi from the Stonesfield slate probably measured 7 feet between the wing-tips. But the largest forms existed apparently towards the close of the Mesozoic period, the pterodactyles of the British Cretaceous rocks and the American Pteranodon being of still larger size : some of them, it is calculated, must have had wings at least 20 feet in extent.

See Buckland, BriAlgewater Treatise, 1836 ; envier, Ossements jossiles, vol. v. pt. 2, p. 359 (1824) ; Huxley, "On Rhamphorhynchus Bucklandi," in Quart. Journ. Geol. Soc., vol. xv. p. 658 (1859), and Anatomy of Vertebrated Animals (1871), p. 266 ; Marsh, "Notice of New Sub-order of Pterosauria (Pteranodon)," Amer. Journ. Sci. and Art, vol. xi. p. 507 (1876), and on the "wings of Pterodactyles," in Amer. Journ. Science, vol. xxiii. p. 251 (1882); Owen, Palwontographical Society (1851, 1859, 1860); Seeley, Ornithosauria (1870); Von Meyer, Reptilien aus dem lithograph. Schiefer [Fauna der Vorwelt] (1859), and Palreontographica, vol. x. p. 1 (1861). (E. T. N.)

Pterosaltria [next] [back] Psychology

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or