The Ornithosauria / An elementary study of the bones of Pterodactyles made from fossil remains found in the Cambridge Upper Greensand, and arranged in the Woodwardian Museum of the University of Cambridge

by H. G. Seeley

[Q] Outer and inner are here used in accordance with the usual interpretation, and the better to compare with birds.

The lateral aspects of the bone are at right angles to the proximal and distal surfaces. They are smooth, a little concave in antero-posterior extent, and convex in the opposite direction. That one on to which the marginal articular surface impinges is except for that surface sub-quadrate in outline; the opposite side has a slightly crescentic form, the flattened outline being distal. They show several small foramina.

The distal aspect of the bone is comparatively flat. The distal surface consists of a smooth unarticular part adjacent to the apex, rather smaller than the corresponding area on the proximal aspect of the bone. Between this part and the sub-crescentic articular surface, which occupies the remainder of the distal area, is a large circular pit, furthest removed from the side of the bone which forms the sub-apical marginal articulation. The pit on the apical side shows several small foramina; on the outer side of the bone the roughened articular surface extends down the pit side. The articulation is flattened from side to side of the bone. Its outer margin is slightly prominent, and the margin of the pit is slightly convex and prominent, so that the intervening articular surface in the direction between these limits is concave. It is commonly divided into two parts by a median band limiting a depressed half, which is in a slightly different plane from the other half of the articulation. Where the depressed part terminates towards the marginal articulation, which does not extend so far distally, there is between the two a small step-like roughened articular portion.

The large crescentic articulation described gave attachment to the wing-metacarpal bone; if there was a second metacarpal terminating in a claw, it must have been attached to the small articulation last referred to. In No. 20 the pit is extremely small, the impressed part of the articulation is small and deeply sunk, while the apicular articulation is widened and shortened so as to make the outline of the bone quadrate.

III. Lateral Carpal.

The tablet exhibits eight examples of a bone which at its distal end is attached to the marginal apicular articulation of the distal carpal, thence extending proximally, and terminating in an articular facet for the third bone of the fore-arm, so as to overlap laterally both of the other carpals. The bone is compressed, is three times as wide as thick, and in outline sub-quadrate with a distal talon. On the inner side it is flat, and on the outer side above the talon it is concave vertically and convex transversely in such way that the side of the bone to which the distal articulation is adjacent is thicker than the other side, and sometimes bent at a sharp angle. The talon on the inner aspect of the bone is flat and continuous with the quadrate side, but on the outer aspect it is separated from the side by an elevated transverse thickening, distally to which the bone is compressed, and rounded into the adjacent parts. The talon extends over more than half of the distal end of the bone, and constitutes with the remainder of the distal end, the distal articulation, which is flat from front to back, and concave from side to base. The proximal articulation is cupped and extends over the whole proximal surface; it is at right angles with the sides of the bone. Both the inner and outer sides exhibit small pneumatic foramina. No. 8 differs from the other specimens in its sub-triangular lateral outline, and general less complex modifications.

The Carpus of the Cambridge Ornithosaurians at first sight is not easily compared with that of Birds; Birds having but one bone between the radius and the metacarpus. But that one bone in the Ostrich, for instance, is not unlike in form to the proximal carpal of Pterodactyle; while the proximal end of the metacarpus presents so close an analogy with the distal carpal of the Pterodactyle, that even were it not easily demonstrated that the bone in Birds commonly called the metacarpus is a carpo-metacarpus[R], it would be strong evidence for such a determination. In Birds there is a small lateral bone between the ulna and carpo-metacarpus which is evidently homologous with the lateral carpal of our Pterodactyles, and so, since this lateral carpal of the Ostrich is the pisiform bone, it results that the lateral carpal of Pterodactyle is the pisiform bone also. From this follows a conclusion of the first importance in the interpretation of the hand. The fine hair-like metacarpals of the Pterodactyle are on the side towards the pisiform bone, while the great wing-metacarpal is on the side towards the index finger.

[R] They separate without difficulty in the Chicken.

In Birds the rudimentary thumb (or second finger, according to Owen) has no connection with the carpus. In the Penguin, Aptenodytes Patagonica, it has disappeared altogether, and there then remain two fingers of which the outer one (seen from the front as we have placed our animal) is the larger, and has the greatest number of phalanges, precisely as in Ornithosaurians. Moreover the wing-metacarpal, in the Penguin especially, is seen to unite with the carpus directly under the radius, as is the case with the Cambridge Ornithosaurians. Hence it follows that in Pterodactyles the thumb is not developed, and that the wing-finger is not the little finger, but the index finger, precisely as in Birds. If Goldfuss gave a reverse arrangement it was because the hand in his specimen, as is proved by the claws, was upside down. In the immature state the distal carpal of Pterodactyle appears to have been composite.