Part 10 (1/2)
Phalanges of the wing finger ________________/________________
I. II. III. IV.
7-3/4 8-1/2 [7?] 6-1/2 } length of each bone 5-1/2 7-3/4 5-1/2 [4-1/2?] } in inches.
4-1/2 ---- ---- ---- }
The femur is represented by many examples--one 3-3/4 inches long, and others less than 3 inches long (2-9/10). In Campylognathus, which has so much in common with the jaw and the wing bones in size, the upper leg bone is 2-8/10 inches. Therefore if we a.s.sign the larger femur to the larger wing, the femur will be relatively longer in all species of Rhamphocephalus than in Campylognathus. Only one example of a tibia is preserved. It is 3-1/2 inches long, or only 1/10 inch shorter than the bone in Campylognathus, which has the femur 2-8/10 inches, so that I refer the tibia of Rhamphocephalus to the species which has the intermediate length of wing. These coincidences with Campylognathus establish a close affinity, and may raise the question whether the Upper Lias species may not be included in the Stonesfield Slate genus Rhamphocephalus.
The late Professor Phillips, in his _Geology of Oxford_, attempted a restoration of the Stonesfield Ornithosaur, and produced a picturesque effect (p. 164); but no restoration is possible without such attention to the proportions of the bones as we have indicated.
OXFORD CLAY
A few bones of flying reptiles have been found in the Lower Oxford Clay near Peterborough, and others in the Upper Oxford Clay at St. Ives, in Huntingdons.h.i.+re. A single tail vertebra from the Middle Oxford Clay, near Oxford, long since came under my own notice, and shows that these animals belong to a long-tailed type like Campylognathus. The cervical vertebrae are remarkable for being scarcely longer than the dorsal vertebrae; and the dorsal are at least half as long again as is usual, having rather the proportion of bones in the back of a crocodile.
LITHOGRAPHIC SLATE
Long-tailed Pterodactyles are beautifully preserved in the Lithographic Limestone of the south of Bavaria, at Solenhofen, and the quarries in its neighbourhood, often with the skeleton or a large part of it flattened out in the plane of bedding of the rock. Fine skeletons are preserved in the superb museum at Munich, at Heidelberg, Bonn, Haarlem, and London, and are all referred to the genus Rhamphorhynchus or to Scaphognathus. It is a type with powerfully developed wings and a long, stiff tail, very similar to that of Dimorphodon, so that some naturalists refer both to the same family. There is some resemblance.
The type which is most like Dimorphodon is the celebrated fossil at Bonn, sometimes called _Pterodactylus cra.s.sirostris_, which in a restored form, with a short tail, has been reproduced in many text-books. No tail is preserved in the slab, and I ventured to give the animal a tail for the first time in a restoration (p. 163) published by the _Ill.u.s.trated London News_ in 1875, which accompanied a report of a Royal Inst.i.tution lecture. Afterwards, in 1882, Professor Zittel, of Munich, published the same conclusion. The reason for restoring the tail was that the animal had the head constructed in the same way as Pterodactyles with a long tail, and showed differences from types in which the tail is short; and there is no known short-tailed Pterodactyle, with wrist and hand bones, such as characterise this animal. The side of the face has a general resemblance to the Pterodactyles from the Lias, for although the framework is firmer, the four apertures in the head are similarly placed. The nostril is rather small and elongated, and ascends over the larger antorbital vacuity. The orbit for the eye is the largest opening in the head, so that these three apertures successively increase in size, and are followed by the vertically elongated post-orbital vacuity. The teeth are widely s.p.a.ced apart, and those in the skull extend some distance backward to the end of the maxillary bone. There are few teeth in the lower jaw, and they correspond to the large anterior teeth of Dimorphodon, there being no teeth behind the nasal opening. The lower jaw is straight, and the extremities of the jaws met when the mouth was closed. The breast bone does not show the keel which is so remarkable in Rhamphorhynchus, which may be attributed to its under side being exposed, so as to exhibit the pneumatic foramina.
The ribs have double heads, more like those of a Crocodile in the region of the back than is the case with the bird-like ribs from Stonesfield.
The second joint in the wing finger may be longer than the first--a character which would tend to the a.s.sociation of this Pterodactyle with species from the Lias; a relation to which attention was first drawn by Mr. E. T. Newton, who described the Whitby skull.
The Pterodactyles from the Solenhofen Slate which possess long tails have a series of characters which show affinity with the other long-tailed types. The jaws are much more slender. The orbit of the eye in Rhamphorhynchus is enormously large, and placed vertically above the articulation for the lower jaw. Immediately in front of the eye are two small and elongated openings, the hinder of which, known as the antorbital vacuity, is often slightly smaller than the nostril, which is placed in the middle length of the head, or a little further back, giving a long dagger-shaped jaw, which terminates in a toothless spear.
The lower jaw has a corresponding sharp extremity. The teeth are directed forward in a way that is quite exceptional. Notwithstanding the ma.s.siveness and elongation of the neck vertebrae, which are nearly twice as long as those of the back, the neck is sometimes only about half the length of the skull.
All these long-tailed species from the Lithographic Stone agree in having the sternum broad, with a long strong keel, extending far forward. The coracoid bones extend outward like those of a Crocodile, so as to widen the chest cavity instead of being carried forward as the bones are in Birds. These bones in this animal were attached to the anterior extremity of the sternum, so that the keel extended in advance of the articulation as in other Pterodactyles. The breadth of the sternum shows that, as in Mammals, the fore part of the body must have been fully twice the width of the region of the hip-girdle, where the slenderer hind limbs were attached. The length of the fore limb was enormous, for although the head suggests an immense length relatively to the body, nearly equal to neck and back together, the head is not more than a third of the length of the wing bones. The wing bones are remarkable for the short powerful humerus with an expanded radial crest, which is fully equal in width to half the length of the bone. Another character is the extreme shortness of the metacarpus, usually a.s.sociated with immense strength of the wing metacarpal bone.
The hind limbs are relatively small and relatively short. The femur is usually shorter than the humerus, and the tibia is much shorter than the ulna. The bones of the instep, instead of being held together firmly as in the Lias genera, diverge from each other, widening out, though it often happens that four of the five metatarsals differ but little in length. The fifth digit is always shorter.
The hip-girdle of bones differs chiefly from other types in the way in which those bones, which have sometimes been likened to the marsupial bones, are conditioned. They may be a pair of triangular bones which meet in the middle line, so that there is an outer angle like the arm of a capital Y. Sometimes these triangular bones are blended into a curved, bow-shaped arch, which in several specimens appears to extend forward from near the place of articulation of the femur. This is seen in fossil skeletons at Heidelberg and Munich. It is possible that this position is an accident of preservation, and that the prepubic bones are really attached to the lower border of the pubic bones.
Immense as the length of the tail appears to be, exceeding the skull and remainder of the vertebral column, it falls far short of the combined length of the phalanges of the wing finger. The power of flight was manifestly greater in Rhamphorhynchus than in other members of the group, and all the modifications of the skeleton tend towards adaptation of the animals for flying. The most remarkable modification of structure at the extremity of the tail was made known by Professor Marsh in a vertical, leaf-like expansion in this genus, which had not previously been observed (p. 161). The vertebrae go on steadily diminis.h.i.+ng in length in the usual way, and then the ossified structures which bordered the tail bones and run parallel with the vertebrae in all the Rhamphorhynchus family, suddenly diverge downward and upward at right angles to the vertebrae, forming a vertical crest above and a corresponding keel below; and between these structures, which are identified with the neural spines and chevron bones of ordinary vertebrae, the membrane extends, giving the extremity of the tail a rudder-like feature, which, from knowledge of the construction of the tail of a child's kite, may well be thought to have had influence in directing and steadying the animal's movements. There are many minor features in the shoulder-girdle, which show that the coracoid, for example, was becoming unlike that bone in the Lias, though it still continues to have a bony union with the elongated shoulder-blade of the back.
[Ill.u.s.tration: FIG. 56. RESTORATION OF THE SKELETON OF _RHAMPHORHYNCHUS PHYLLURUS_
From the Solenhofen Slate, partly based upon the skeleton with the wing membranes preserved]
[Ill.u.s.tration: FIG. 57. RESTORATION OF THE SKELETON OF _SCAPHOGNATHUS CRa.s.sIROSTRIS_
Published in the _Ill.u.s.trated London News_ in 1875. In which a tail is shown on the evidence of the structure of the head and hand]
[Ill.u.s.tration: FIG. 58. SIX RESTORATIONS
1. Ramphocephalus. Stonesfield Slate. John Phillips, 1871 2. Rhamphorhynchus. O. C. Marsh, 1882 3. Rhamphorhynchus. V. Zittel, 1882 4. Ornithostoma. Williston, 1897 5. Dimorphodon. Buckland, 1836. Tail then unknown 6. Ornithocheirus. H. G. Seeley, 1865]
The great German delineator of these animals, Von Meyer, admitted six different species. Mr. Newton and Mr. Lydekker diminish the number to four. It is not easy to determine these differences, or to say how far the differences observed in the bones characterise species or genera. It is certain that there is one remarkable difference from other and older Pterodactyles, in that the last or fourth bone in the wing finger is usually slightly longer than the third bone, which precedes it. There is a certain variability in the specimens which makes discussion of their characters difficult, and has led to some forms being regarded as varieties, while others, of which less material is available, are cla.s.sed as species. I am disposed to say that some of the confusion may have resulted from specimens being wrongly named. Thus, there is a Rhamphorhynchus called curtima.n.u.s, or the form with the short hand. It is represented by two types. One of these appears to have the humerus short, the ulna and radius long, and the finger bones long; the other has the humerus longer, the ulna much shorter, and the finger bones shorter. They are clearly different species, but the second variety agrees in almost every detail with a species named hirundinaceus, the swallow-like Rhamphorhynchus. This identification shows, not that the latter is a bad species, but that curtima.n.u.s is a distinct species which had sometimes been confounded with the other. While most of these specimens show a small but steady decrease in the length of the several wing finger bones, the species called Gemmingi has the first three bones absolutely equal and shorter than in the species curtima.n.u.s, longima.n.u.s, or hirundinaceus. In the same way, on the evidence of facts, I find myself unable to join in discarding Professor Marsh's species phyllurus, on account of the different proportions of its limb bones. The humerus, metacarpus, and third phalange of the wing finger in _Rhamphorhynchus phyllurus_ are exceptionally short as compared with other species.
Everyone agrees that the species called longicaudus is a distinct one, so that it is chiefly in slight differences in the proportions of const.i.tuent parts of the skeleton that the types of the Rhamphorhynchus are distinguished from each other. I cannot quite concur with either Professor Zittel (Fig. 58, 3) or Professor Marsh (Fig. 58, 2) in the expansion which they give to the wing membrane in their restorations; for although Professor Zittel represents the tail as free from the hind legs, while Professor Marsh connects them together, they both concur in carrying the wing membrane from the tip of the wing finger down to the extremity of the ankle joint. I should have preferred to carry it no further down the body than the lower part of the back, there being no fossil evidence in favour of this extension so far as specimens have been described. Neither the membranous wings figured by Zittel nor by Marsh would warrant so much body membrane as the Rhamphorhynchus has been credited with. I have based my restoration (p. 161) of the skeleton chiefly on _Rhamphorhynchus phyllurus._
THE SHORT-TAILED TYPES