  BY S. W. WILLISTON. PART I, WITH PLATE I. The first American species of the singular group of extinct Mesozoic reptiles variously know as Ornithosaurs, Pterosaurs or Pterodactyls was described by Marsh from a fragmentary specimen obtained in 1870, by the Yale College Expedition in Wallace County, Kansas. About a dozen other specimens were obtained by a similar expedition the following year in charge of Professor Marsh, or by Professor Cope, and were described by these authors shortly afterward. By far the largest number of known specimens, however, other than those in the Kansas University Museum, were obtained during the years 1874, ’75, ’76 and ’77 by parties of which Professor Mudge, Dr. H. A. Brous, E. W. Guild, George Cooper and myself were the members, and it was from these specimens that most of the published characters were derived. Many of these specimens are necessarily fragmentary ones, still the material now in the Yale College Museum is ample to elucidate everything of interest concerning these animals. During the past few years, the Museum of Kansas University has been enriched by a series of excellent specimens of these animals, obtained from the same regions, specimens that permit the solution of most of the doubtful characters and throw not a little light on the affinities of the Kansas forms. The species hitherto named are as follows: PTERANODON.Pteranodon Marsh, Amer. Journ. Sci. xi, p. 508, June 1876; and xii, p. 479, Dec. 1876; xxiii, p. 253, April, 1882; xxvii, p. 423, May, 1881; Williston, Amer. Naturalist, xxv, p. 1174, Dec. 1891 Pteranodon occidentalis.Pterodactylus Oweni Marsh, Amer. Journ. Sci. i, p. 472, June 1871, Sep. p. 16 (nom. preoc). Pterodactylus occidentalis Marsh, Amer. Journ. Sci. iii, p. 242, April 1872, Sep. p. 1; Cope, Cretac. Vert. p. 68, pl. vii, ff. 5, 6. Ornithocheirus harpyia Cope, Proc. Amer. Phil. Soc. 1872, p. 471 (Cope). This species was originally based upon the distal end of two wing-metacarpals, and teeth. In the following year, a fuller description was given of additional remains referred to the same species and renamed P. occidentalis. Pteranodon ingens.Pterodactylus ingens Marsh, Amer. Journ Sci. iii, p. 246, April 1872, Sep. p. 6. Pteranodon ingens Marsh, Amer. Journ. Sci. xi, p. 508, June 1876. This species is based upon various bones of the wing-finger of several individuals, and three teeth. Pteranodon umbrosus.Ornithocheirus umbrosus Cope, Proc. Amer. Phil. Soc. 1872, p. 471. Pterodactylus umbrosus Cope, Cret. Vert. p. 65, pl. vii, ff. 1-4. Marsh (Amer. Journ. Sci. xii, p. 480, Dec. 1876) says this name is a synonym of P. ingens, published two days earlier. As this synonymy is not certain, and as Cope’s species has been figured, I am not ready to accept his views. Pteranodon velox.Pterodactylus velox Marsh, Amer. Journ. Sci. iii, p. 247, April 1872, Sep. p. 8. Based upon the distal end of the right metacarpal of the wing-finger, and the proximal extremity of the adjoining first phalanx, two uncharacteristic parts of the skeleton, Marsh to the contrary notwithstanding. It is doubtful whether the direct comparison of the types will suffice to determine the species with certainty. “Both of the bones are somewhat distorted by pressure.” Pteranodon longiceps.Pteranodon longiceps Marsh, Amer. Journ. Sci. xi, p. 508, June 1875; xxvii, p. 424, pl. xv, May 1884. Based upon a somewhat defective skull, without other bones. There is no evidence whatever that the species is distinct from the preceding. Pteranodon comptus.Pteranodon comptus Marsh, Amer. Journ. Sci. xi, p. 509, June 1876. Based upon wing-bones of three individuals. The description is meagre. Pteranodon nanus.Pteranodon nanus Marsh, Amer. Journ. Sci. xxi, p. 343, April 1881. Based upon various remains of one individual; the humerus, alone, is recognizably described. NYCTODACTYLUS.Nyctosaurus Marsh, Amer. Journ. Sci. xii, p. 480, Dec. 1876. (nomen preoc. Nyctodactylus Marsh, Amer. Journ. Sci. xxi, p. 343, April 1881: ibid. xxvii, p. 423, May 1884. Nyctodactylus gracilis.Pteranodon gracilis Marsh, Amer. Journ. Sci. xi, p. 508, June 1876. Nyctosaurus gracilis Marsh, Amer. Journ. Sci. xii, p. 480, Dec. 1876. Nyctodactylus gracilis Marsh, Amer. Jour. Sci. xxi, p. 343, April 1881. PTERANODON.Skull.Fragmentary portions of the skull of Pteranodon are not at all rare in the Kansas chalk; but it is exceedingly seldom that a complete, or even approximately complete specimen is found. Their great length and slenderness, together with the extensive pneumaticity of the bones, render their preservation, as a whole, a thing of great rarity. Probably the most nearly perfect one yet known is now in the Museum of Kansas University. It was discovered the past summer by Mr. E. C. Case, a member of the University Geological Expedition. The specimen was carefully cleaned on its upper surface, as it lay in the chalk, and then imbedded in plaster before removal. The surface now exposed was the under one, which surface is, almost invariably, better preserved and less distorted than the upper one in these animals. A figure of this specimen is given in Plate I. The only portion restored is that indicated by the line in the lower jaw; it is possible that this part of the symphysis may not be exactly as it is drawn. Other, incomplete, specimens in the Museum confirm the outlines, except in the occipital crest, which is not present. As stated by me in the American Naturalist (l. c.), the type specimen of Pteranodon, also collected by myself, was incomplete, and the figures of it, as given by Marsh, are faulty. The elements of the skull are all so firmly united that they can not be distinguished. There are no indications whatever of a horny sheath enclosing the jaw, and it is improbable that the covering of these parts was essentially different from that in the slender jawed Pterodactylidae. In texture, the maxillaries are fine-grained, and wholly without the vascular foramina found in the corresponding bones of birds. The bones are composed of two thin and firm plates, separated by cavities which are bounded by irregular walls of bony tissue. In the compression from which all the Pterodactyl bones have suffered more or less, the greater resistance of these walls has caused irregularities upon both the outer and the inner surfaces. At the borders of the bones, where the thickness has been greater, the roughening is not observed. Seen from above, the skull is narrow, as stated by Marsh; but, contrary to his statement, there is not a sharp ridge extending along the upper border. This border is obtuse and rounded, and in the frontal region, flattened. The sagittal crest is large, but not nearly so large as it is figured by Marsh, the restored outline of whose figure is undoubtedly wrong. The texture of the bone forming the crest is materially different from that of the remaining bones of the skull. The bone is more roughened, and less firm. There is a well-developed ring of sclerotic ossifications. In the specimen figured, the separate plates measure from six to eight millimeters in diameter. They were not imbricated, as in the Pythonomorpha, but have a similar dense texture. There is a superior temporal arch, bridging over a small opening leading downward to the inferior temporal fossa. The following measurements will give the principal dimensions of this specimen.
Pubis.In a previous paper on the anatomy of Pteranodon, Book Cover. FIG. 1. The principal measurements of the above described specimen are as follows:
NYCTODACTYLUS.The type species of this genus was described as follows by its author (loc. cit. supra): “One of the smallest American species yet found is represented in the Yale Museum by several bones of the wing, a number of vertebrae and the nearly complete pelvis. The wing-bones preserved are elongated and very slender. The pelvis is unusually small, and there are five vertebrae in the sacrum. The last of the series indicates that the tail was short. The following are the principal measurements of this specimen:
This species, which may be called Pteranodon gracilis, was about two-thirds the size of P. velox Marsh. It probably measured about ten feet between the tips of the expanded wings.” In the December number of the same volume of the American Journal of Science, he described the genus as follows: “A second genus of American Pterodactyls is represented in the Yale Museum by several well preserved specimens. This genus is nearly related to Pteranodon, but may be readily distinguished from it by the scapular arch, in which the coracoid is not co-ossified with the scapula. The latter bone, moreover, has no articulation at its distal end, which is comparatively thin and expanded. The type of this species is Pteranodon gracilis Marsh, which may now be called Nyctosaurus gracilis. It was a Pterodactyl of medium size, measuring about eight to ten feet between the tips of the expanded wings.” The specific description of this species rests solely upon the measurements; the other characters given are not only vague, but are also common to all the known species. The generic description, as it is seen, is based upon the structure of the coraco-scapula. It will also be observed that the characters are not drawn from the type specimen, as that did not include this part of the skeleton, according to the author’s statement. Of these two characters, the non-ossification of the coracoid and scapula is a somewhat doubtful one, as the same character may or may not occur in allied species, as, for example, in the species of Rhamphorhyncus (R. Muensteri Goldf.) described by the author himself. So incomplete and unsatisfactory are the characters thus given that Zittel, in his Handbuch, dismisses the genus with the brief remark, “noch unbeschrieben.” Nevertheless, from the peculiar form of the scapula, and from my recollection of the specimens upon which the genus was based, I believe I have determined with certainty an excellent specimen in the Snow Museum of Kansas University as a member of it, and here give a sufficiently complete description to place the genus on a more secure foundation. This specimen was collected by Professor E. E. Slosson, of Wyoming University, while a member of my party in western Kansas the past season. It was partly exposed upon a gently sloping surface of firm yellow chalk on the Smoky Hill river, in the vicinity of Monument Rocks. Originally, the nearly complete skeleton must have been preserved, but a number of the bones had been either wholly or partially washed away, in some cases leaving their imprint in the chalk. The bones uncovered, and now lying upon the chalk slab nearly in their natural relations, are a humerus, both radii and ulnae, a pteroid, the two carpals of one wrist, both wing metacarpals, a first and a last wing phalanx, both coraco-scapulae, the posterior part of the lower jaws, ilium, femur, sternum, numerous ribs and vertebrae. The two coraco-scapulae lie with their scapular ends nearly touching, and their coracoid ends separated by a space equivalent to the width of the sternal articulation. The two elements appear to have been imperfectly united and were probably not co-ossified. The inferior border of the The sternum lies at a little distance from the coraco-scapulae. It is an extremely thin bone, with a stout anterior, styliform projection, at the base of which, on either side, looking upward and outward, is the articular, trochlea-like surface for the sternal end of the coracoid. The width between these articular surfaces measures fifteen millimeters; the length of the process in front of the articulations is twenty-five millimeters. Immediately posterior to the articular surfaces, the bone expands nearly at right angles to the longitudinal axis to a width of about sixty millimeters. The thin lateral margins are nearly parallel with the longitudinal axis, and show three shallow emarginations between the four costal articular projections. The hind angles are nearly rectangular. The bone, as preserved, is only shallowly concave, and shows no true keel, though a more pronounced median convexity towards the front doubtless subserved the function of a carina in part. The left humerus lies in position, and is especially characterized by its enormous deltoid crest (radial crest of Marsh), though otherwise slender. This crest is further removed from the head of the bone than is the case in species of Pteranodon. It is directed somewhat downward, and has its distal, gently convex, border about twenty-five millimeters in extent, while the width of the process midway between the extremity and the base measures but sixteen millimeters. The bicipital crest is also prominent. The bone is relatively shorter than in Pteranodon. The humerus, as will be seen from the above description, and from the measurements given below, is remarkably like the same bone in Pteranodon nanus, as described by Marsh (l. c. supra), and but a little larger. In P. nanus, however, the coracoid and scapula are said to be firmly co-ossified, and the scapula has of course a different structure. The skull has been, unfortunately, almost wholly washed away, a fragment of the cranial wall and the posterior part of the lower jaws alone remaining. It is impossible, hence, to say much concerning this part of the anatomy. The lower jaws show a different structure from that in Pteranodon. As they lie in their natural position, the width at the condyles is about twenty-four millimeters. The angular is less produced posterior to the articulation than in Pteranodon, indicating a less elongated and less powerful mandibular portion, an indication further borne out by the slenderness of the rami. The impression in the chalk shows the symphysis to begin ninety millimeters from the articulation. The width at this place could not have exceeded sixteen millimeters; and the entire length of the lower jaws could hardly have been more than one hundred and twenty-five millimeters. In the parts preserved, measuring seventy-five millimeters, there are no indications of teeth; yet it is not impossible that there may have been teeth in the anterior portion of the dentary, as in some species of Pterodactylus. I hardly think it probable, however. There are seven cervical vertebrae preserved, apparently the full complement, as in Pteranodon and other members of the order. They differ in no especial respect from the corresponding vertebrae of Pteranodon, and, apparently, of Pterodactylus. The imperfectly anchylosed, possibly free, atlas shows three pieces, the odontoid process and the two slender lateral pieces. The lateral pieces are entirely free, with a thickened base and a slender, curved upper portion. The odontoid is gently concave in front, and seems to be imperfectly ossified with the axis; it occupies the lower part of the articulation, corresponding to the hypapophysis of the Pythonomorpha. The axis is the shortest of the remaining vertebrae, and has a well developed spine. The centrum is strongly convex behind, as are the remaining centra of the series. The following five vertebrae decrease gradually in length. The anterior ones have only a thin ridge or plate for the neural spine; the seventh, however, has a neurapophysis of some length. They are all, as is usually the case, somewhat distorted from pressure. The under side is flattened, apparently gently concave longitudinally, and with a lateral ridge terminating in an obtuse hypapophysis at each inferior hind angle. In his discussion of the Pterosauria, Zittel says concerning the vertebrae: “zwischen oberen Bogen und Centrum ist keine Sutur zu bemerken.” Handbuch, iii, p. 776. In this he is in error, so far as the American forms are concerned. It is usually the case in the Kansas specimens of both genera that the neural arch of the post-cervical vertebrae is wholly or in part detached from the centrum, showing a Two other vertebrae (b), found close by the one just described, and possibly one or the other contiguous with it, differ remarkably in having no, or a rudimentary, parapophysial process, and in having the diapophyses much shorter. It is not impossible that a slight expansion at the lateral margins of the ball may represent small parapophyses. In Pteranodon there are at least four vertebrae with dia- and parapophyses. In the other vertebrae from this region the diapophyses are yet shorter and the neural spine stouter and broader. The other centra preserved are all shaped somewhat like the half of a cylinder, and are a little longer than broad. They have no distinct cup or ball. In two of them there is a very long, recurved parapophysial process, as though formed by an anchylosed rib, on each side; they are probably lumbar vertebrae. Most of the ribs are very slender; a few are moderately thickened; one only is very stout; its measurements are given below.
The principal dimensions of this species can be got at with considerable certainty. Although two of the wing-phalanges and the bones of the foot are wanting, yet the relative proportions of those present agree so closely with those of the corresponding bones in Pteranodon, that there can be but little possibility of error in assuming the same proportions for the missing ones. The position of the ilium and femur, as also the ribs, show that they hold their natural relations to the pectoral arch. The tail, alone, can not be got at.
But one species has been described from the American Cretaceous smaller than the present one, Pteranodon nanus Marsh, in which the expanse of wings is given as not more than three or four feet. In this estimate the author is certainly in error. The size of the humerus, as given, is rather more than three-fourths that of the present species, and the expanse, hence, must be nearly five feet in life, or six feet as the bones lie outstretched. As regards the specific determination of the present specimen, there must necessarily be some doubt until the species already named have been recognizably described. But three of the existing species can be taken into account, N. gracilis, P. comptus and P. nanus. That it can not be the last, has already been shown. In size, it agrees well with P. comptus, but the other characters throw no light upon the identity. The measurements given of the type specimen of N. gracilis show the size to be materially greater,—a character, however, of subordinate value—greater slenderness, and a relatively shorter first wing-phalanx. The relative lengths of wing-metacarpals, wing-phalanx and ulna in N. gracilis and the present specimen may be expressed as follows:
It will be seen that not a single character has yet been given to distinguish the genus from Pterodactylus, and it is not at all impossible that it may prove to be the same; its location among the Pteranodontidae rests solely on the assumed absence of teeth, and that is a character yet wholly unknown. The material now in the museum permits a fuller discussion of the relations and characters of this group of reptiles than has been hitherto attempted. Originally, they were described as constituting a new order, a view still held by its author and no one else. Lydekker, in his Paleontology and Catalogue gives them a subordinal value; Zittel only a family value, though expressing doubt as to their subordinal rank. It seems very probable that the genus Nyctodactylus has no teeth in the jaws; it agrees in every other respect with the genus Pterodactylus, so far as known. If the genus has teeth it must be united with Pterodactylus. Now, in not a few species of this genus, the teeth are confined to the anterior end of the jaws, and their entire absence, unaccompanied by other structural differences, will hardly constitute an order, or even family. But, leaving aside Nyctodactylus, it is very much of a question whether the differences between Pterodactylus and Pteranodon are sufficient to locate them in different families, let alone different suborders. The two genera have the following in common: Tail short. Skull with more or less elongated, pointed jaws, and very small upper and lower temporal fossae. Narial opening large, confluent with the pre-orbital foramen. Cervical vertebrae elongated, with rudimentary spinous processes. Fore and hind extremities, quite alike. Pteranodon differs from Pterodactylus, so far as that genus is known, in the united coracoscapulae and pubes, both of which characters are found in Rhamphorhynchus. The sole family characters remaining then, for Pteranodon, are, absence of teeth, a supra-occipital crest, and the articulation of the upper end of the scapula. Now it seems evident that to place the pteranodonts in a group equivalent to all the other pterosaurs is unwarranted, and any classification that will not show the more pronounced relationships with Pterodactylus is faulty. I would, therefore, propose the following:
As regards the geographical distribution of the Pteranodonts, they have hitherto been recognized only from Kansas, but I am firmly of the opinion that they occur in Europe, and, if so, it is very probable that the name Pteranodon must be eventually given up. In fact, a toothless form of Pterodactyl was described by Seeley as long ago as 1871, under the name of Ornithostoma. I cannot refer to his description at present, and can, therefore, give no opinion as to their identity. It seems certain that the peculiar form of the scapulae and their vertebral articulation In view of the above, the practice of the American text-books in Geology in introducing generic names of characteristic fossils as names of the geological horizons whence they come, is very reprehensible, in my opinion. Even the late edition of Leconte’s Elements contains a long list of such names, the greater portion of which have been relegated to the limbo of synonymy by paleontologists. It is greatly to be desired that the name “Pteranodon Beds” shall not become established, so long as there is the least doubt of the validity of the name itself. |
|
