Some Amphibian and Reptilian Remains
from South Africa and Australia
Quarterly Journal of the Geological Society,
vol.xv 1859, pp. 642-649.
Scientific Memoirs II
(Read March 13rd, 1859)
PLATES XXI, XXII. [PLATES 7, 8]
[120] AT the Evening Meeting of this Society held on the 17th of November, 1858, a paper by Mr Stow "On Some Fossils from South Africa" was read. In the course of the discussion which followed, my opinion as to the nature of one of those fossils was asked. With so much reserve as was due to the cursory character of my examination of the remains, I expressed my conviction that the organism in question was the skull of a Labyrinthodont Amphibian, and briefly stated the grounds upon which I based that conclusion. The Chairman of the Meeting then called upon me to undertake a thorough investigation of the matter; and I now report the results of my inquiries in the first of the following papers, in which I have embodied incidentally, the description of an allied Australian Amphibian.
1. On Micropholis Stowii and Bothriceps Australis.
Micropkolis Stowii.—The skull in question is 1/58 inch long, and has, when viewed from above, a parabolic outline l. (Pl. XXI. [Plate 7.] fig 1) or it might be compared to the half of a long ellipse, half of the longer diameter of which is to its shorter diameter as 13 to 10. The bony plates which formed the roof of the skull (fig. 1) have entirely disappeared, as have those which constituted the greater part of its right lateral parietes; but on the left side (fig. 2), the lateral walls are in a tolerably good state of preservation.
The matrix has split in such a manner that that portion of it [121] which is bounded by the contour of the skull has separated from the rest, leaving in its concave counterpart the outer bony crust of the mandible and a portion of the maxillary bones. I had hoped that the fossil might be relieved in such a manner as to show, not only the structure of the under part of the skull, but the character of the occipital articulation; but the matrix is so exceedingly hard, and the bony matter so soft and fragile, that even my experienced and skilful ally, Mr. Dew, was afraid of carrying on his excavations sufficiently far to attain these objects.
Sufficient has been done, however, to reveal the indistinct remainder of the anterior part of the vertebral column, and to prove, by its means, at what point the occipital region of the skull was situated. From this it appears that the postero-lateral angles of the cranium were produced for 3/8ths of an inch behind the general plane of the occipital surface.
The most striking features in the skull are the large oval orbits, which occupy, as nearly as may be, the middle third of the space between the occiput and the end of the snout. The long axes converge a little anteriorly; and the interorbital space (which is not equal to more than one-fourth of the diameter of the skull), opposite the middle of the orbits, is far narrower than the transverse diameter of the orbit.
The nostrils are rounded apertures, distant less than twice their own antero-posterior diameter from the anterior edge of the orbit; they are placed very near the anterior edges of the snout, and are separated transversely by an interval equal to the interorbital space. Their long axes are, like those of the orbits, directed obliquely inwards and forwards. Both orbits and nostrils look upwards and outwards, the former direction predominating. The vertical diameter of the skull (including the mandible) is greatest posteriorly; but even here the thickness does not attain one-fourth of the length; and the vertical diameter gradually diminishes anteriorly, until, at the end of the snout, the thickness does not exceed an eighteenth of the length.
The left premaxillary bone appears to be nearly entire. It is very short, its horizontal portion extending backwards only to the middle of the external nostril, the anterior part of whose inferior boundary it forms. At its inner end, the premaxilla gives off a broad but short, ascending, recurved process, which forms the anterior and internal boundary of the external nostril and ends superiorly in a point. Whether it is broken off here, or not, I cannot say.
The maxilla meets the posterior end of the premaxilla, and then [122] extends backwards beneath the orbit to the posterior margin of the jugal bone, where its bony matter disappears. The maxilla is widest midway between the nostril and orbit, where it sends up a short obtuse process.
Immediately above this portion of the maxilla lies a broad flat bone (Pl. XXI. [Plate 7] fig. 2), circumscribed on three sides by a zigzag suture, whose posterior free edge forms the anterior boundary of the orbit, while its anterior margin does not quite reach the posterior boundary of the external nostril. Its upper edge unites with a fragment of bone whose anterior end enters into the boundary of the nostril. Inferiorly and behind, it is in contact, for a small extent, with a bone (the jugal) which completes the boundary of the orbit below; and, in front of this point, it either comes into relation with the maxilla, or is separated from it by an elongated bone which completes the boundary of the nostril anteriorly. I put the alternative because I do not feel certain whether a particular line, which seems to be a suture, is one or not. If the elongated strip of osseous matter in question be a distinct bone, it corresponds with that termed by Von Meyer "lacrymal" in the Labyrinthodonts.
The bone bounded by the zigzag suture is in all probability the prefrontal, while the upper fragment connected with it is apparently all that remains of the nasal.
The jugal bone (Pl. XXI. [Plate 7] fig. 2) narrows as it passes back from its connexion with the prefrontal, becoming very slender where it forms the lowest part of the orbital wall. Indeed it here exhibits a discontinuity; but I believe this to be the result of fracture. At the posterior part of the orbit it expands into a broad plate, whose anterior concave margin forms half of the posterior boundary of that cavity. Its inferior margin unites with the maxillary, and then with a small triangular plate of bone interposed between it and the end of the maxillary (quad-rato-jugal?). Its superior margin is divided into two parts, an anterior, nearly horizontal, which unites with a slender plate of bone whose anterior end forms part of the boundary of the orbit, and seems to be all that is left of the bone called "Post-orbital" (Hinteraugenhohlen-knochen) by Von Meyer; and a posterior moiety, which shelves downwards and backwards and articulates with another fragmentary bony plate, whose upper part occupies the superior and external angle of the skull, while its lower part becomes lost in the outer surface of the mass of matrix which has filled the cavity formed by the quadrate and other bones, and is the representative of the suspensorial apparatus of the lower jaw. This bone is obviously the squamosal.
[123] On the left side, the bones which should constitute the lower end of the mandibular suspensorium have almost entirely disappeared, a small fragment only of the quadratum remaining. On the right side, however, a considerable proportion of the quadratum is preserved (Pl. XXI. [Plate 7] fig. 4). Its articular end, 3/16th of an inch broad, and flattened from above downwards, exhibits a condyloid surface which is divided by a groove into a stronger internal, and a less prominent external portion. In front of the condyles the quadratum is very thin, but it rapidly expands, so as to cover all that remains of the flat lateral face of the suspensorium, and extends forward to about midway between the articular condyle for the mandible and the posterior margin of the orbit. At this point the bony matter disappears. On the top of the skull all the osseous matter has vanished except two white lines, one on each side of the interorbital space (representing the upper edges of the orbito-sphenoids ?), and a sinuous transverse line faintly indicating the contour of the occiput (Pl. XXI. [Plate 7] fig. 1).
The lower jaw (figs. 2, 4, 5) has the same general outline as the anterior and later contours of the skull. Its rami are slender in front, but deep and strong posteriorly, where there is a faint indication of a coronoid elevation, in correspondence with which the inferior margin of the suspensorial peduncle is slightly excavated. Behind this the ramus rapidly narrows to its posterior extremity, which extends very little beyond that of the quadrate bone. At the symphysis, the dentary element of the mandible is very distinct and is rather less than 1/8th of an inch in width; it extends back, becoming more slender as it goes, along the upper edge of the mandible. Its posteior boundary cannot be exactly traced; but the backward continuation of the series of teeth with which it is beset testified to its elongation beyond the level of the posterior margin of the orbit. The symphysial end of each dentary bone is conave and produced into a short process posteiorly, so that the union of the two rami would see to have been somewhat lax (fig. 3).
The counterpart of the fossil (figs. 1, 2, 3) just described exhibits the denrary bone of the right ramus in transverse section. It is triangular, with a thin internal edge and a flat upper surface. The teeth are set in apparently distinct aveoli along its outer moiety; and beneath them runs a canal filled with matrix.
A second osseous element of the mandible, the angular bone, extends on the inner side of the jaw to within 3/16ths of an inch of the symphysis. It is trough-like (fig 5), consisting of an internal and an external lamella, united at an angle below, and it appears to [124] extend back nearly to the extremity of the ramus. The precise boundaries of the third distinguishable component of the mandible, the articular bone, are not to be made out; but on the left side, the matrix which fills the posterior end of the ramus extends forwards, becoming narrower untril it ends by a slender rounded extremity, coated with a bony sheath, between the angular and the dentary, and near the anterior termination of the latter. On the right side, in the counterpart, the section of this style-like process of the matrix is seen, and seems to be connected with a narrow bony plate, which appears on the inner side of the ramus between the dentary and the angular.
The posterior end of the articular element is broad and somewhat produced internally, so as to afford sufficient space for the adjustment of the wide articular end of the suspensorial peduncle.
On the under surface of the skull (fig. 3), a whitish patch may be observed on the inner side of the anterior part of the right ramus of the mandible, and a much larger transverse band, of a similar aspect, stretches from the posterior part of the left ramus, two-thirds of the way across to the opposite one.
When these patches are minutely examined, they are seen to consist of a multitude of small, flat, polygonal scutes, of very various dimensions and forms, but none exceeding 1/16th of an inch in diameter. These minute scutes are fitted together by their edges; and their surfaces are marked by irregular grooves and pits, which are so disposed as to leave a narrow, clear margin (fig. 7).
Between the posterior extremities of the rami, the same surface of the fossil exhibits on each side the indistinct impression, and part of the bony substance, of a broad, flat, triangular plate, whose base is turned inwards, and whose apex is produced and bent upwards. Two other fragmentary bones, of apparently a similar character, lie behind these; and still further back, on the counterpart, are the remains of what I take to be a portion of the pectoral arch and its appended member; but the parts are so indistinct and fragmentary that it would be vain to describe them particularly.
The teeth (fig. 6) are very numerous and close-set, slender, conical, sharply pointed, and either straight or concave inwards. They are stronger in the lower jaw than in the upper, and in the anterior than in the posterior part of the lower jaw. I could observe no distinct traces of those longitudinal grooves which characterize the teeth of the larger Labyrinthdonts; but they seem to have possessed a large pulp-cavity. While the teeth of the mandible appear (as I have said) to be lodged in distinct though shallow alveoli, those of the [125] upper jaw seem to be completely anchylosed with the bony walls of the jaw, so as to look like mere processes of it. I would be understood to speak with considerable hesitation on these points, however, the parts being but very imperfectly preserved.
It is at once obvious that the skull which I have just described could have belonged to no true Reptile, but is either that of an Amphibian or that of a Fish.
The composition of the lower jaw, the characters of the teeth, the well-developed nasal apertures, and the arrangement of the bones in the temporal region leave no doubt in my mind as to which of the latter alternatives is to be preferred, and satisfactorily prove the amphibian affinities of the fossil.
Such being the case, there is but one order of the Amphibia, as they are at present arranged, to which it can be referred—the Labyrinthodonta,—with a knowledge of whose characteristic peculiarities, so much of the structure of the skull as can be made out becomes readily intelligible. Thus, in shape and in the position of its orbital and nasal apertures, the African fossil presents a certain resemblance to the German Labyrinthodont Metopias, and to the imperfectly known Russian Rhinosaurus. The arrangement of the cranial and facial bones, and their ornamentation, coincide very well, so far as they go, with the corresponding features of those Labyrinthodonts which have been best studied; and the peculiarities of the jugal, postorbital, and squamosal bones are especially characteristic. Again, I should hardly have ventured to interpret so confidently the appearances presented by the mandible, had I not recently had an opportunity of studying the composition of its articular moiety in some portions of very large mandibles of Labyrinthodon, or Mastodonsaurus, from Warwickshire. I find, from these fossils, that the articular element of the Labyrinthodont jaw (in these genera at any rate) sends a hollow bony prolongation (at first probably a mere osscous sheath around Meckel's cartilage) for a long distance towards the symphysial end of the jaw; and I suspect that the cone of matrix which I have described above is nothing but the cast of a similar prolongation. In the Warwickshire Labyrinthodont, a strong process, formed partly by the angular and partly by the articular bone, is given off inwards and forwards from the posterior part of the inner surface of the ramus; and this is perhaps represented by the inward production of the posterior part of the ramus of the mandible in the African fossil. On the other hand, the great Labyrinthodonts have a very distinct angular process prolonged backwards behind the articulare, and composed in great measure of a process of that [126] element, as in the Crocodile—a structure of which I see no trace in the fossil under consideration.1
The large bony plates under the throat suggest a comparison with the similarly proportioned bony plates which occupy a like position in so many of the better-known Labyrinthodonts, such as Mastodonsaurus, Archegosaurus, &c. Of these plates, however, there are only three, a median (rhomboidal), and two antero-lateral (triangular and bent up at the sides); while the present fossil seems to exhibit the remains of four plates, in two pairs, all of which have the form of triangles with their bases inwards. I am inclined to think that these parts are, in fact, the remains of a hyoidean system, possibly indicating a long persistence of the branchial apparatus.
The teeth, in their even size, their very large pulp-cavities, and the apparent absence of folds of their dentine, are not much like those of the typical Labyrinthodonts; but it must not be forgotten that our own Red Sandstone series2 contain a Labyrinthodont (the so-called Labyrinthodon Bucklandi) which is a totally distinct generic form3 from any of the described Labyrinthodonts, and has close-set, conical, thin-walled teeth, so anchylosed with the upper jaw as to appear continuous with it.
But the Labyrinthodont remains to which the African skull presents the closest resemblance are the Brachyops laticeps of Central India, and the undescribed cranium of an animal (from Australia) in the British Museum, very closely allied to Brackyops.
Brachyops laticeps has been already so fully described by Professor Owen4 that I need merely refer to his paper and to the figures accompanying it: by studying these any person may convince himself of the general resemblance between the Indian and the African fossil, and, at the same time, of the clear differences which separate them generically.
The precise locality whence the Australian skull was obtained is unknown; and I should have remained ignorant of its existence except for the kindness of my friends Mr. Waterhouse and Mr. [127] Woodward, the latter of whom, being present when I gave a short description of the African fossil to the Society, was struck with its resemblance to the skull in the British Museum.
Bothriceps Australis.—In the Australian fossil (Pl. XXII. [Plate 8] fig. 1) the bony matter has almost wholly disappeared from the roof of the skull, except near the occiput, where a patch of it remains in the supraoccipital region, and is sculptured like the corresponding part of a Crocodile's skull, exhibiting irregular close-set, but separate, polygonal pits. The cranium measures four inches in length, from the extremity of the snout to the end of the occipital condyles, and its greatest breadth between the ends of the mandibular suspensoria is 3-3/4 inches; the greatest depth of the skull is at its posterior end, and does not exceed 11 inches, so that it is very flat (fig. 2). The margins of the left orbit are much broken; but those of the right orbit seem to be nearly entire. It is oval, with its long axis directed forwards, nearly parallel with that of the skull; it measures 7/8ths of an inch in breadth, 5/8ths of an inch in width, and it occupies as nearly as possible the middle of the space between the superior margin of the occiput and the anterior edge of the premaxilla. The interorbital space appears to have measured about an inch in width. The posterior margins of the large rounded nasal apertures are distant about 3- 3/4ths of an inch from the anterior margin of the orbits; and the interspace between the nostrils is about half an inch.
The surface of the matrix exhibits impressions of the sutures which separated the constituent bones of the skull. Two nasals, two large frontals, and a single or double parietal are clearly traceable in the middle line. The middle of the anterior half of the parietal region is marked by a strong longitudinal depression, which occupies nearly one-third of its width, and ends, posteriorly, in the parietal foramen, while anteriorly it is continued forwards, becoming shallower, on to the frontals. The post-frontal bounds most of the inner and a little of the posterior margin of the orbit, while almost the whole of the remaining posterior boundary is filled up by the postorbital bone. Posteriorly and externally, this joins the squamosal; while posteriorly and internally, a bent sutural line separates it from a bone which is called "squamosum" by Von Meyer, Archegosaurus, and "second parietal" by Professor Owen in Brachyops. This bone and the squamosal unite posteriorly with a pyramidal bone which resembles in form and position the bone called "occipital externe" in Fishes by Cuvier. The exoccipitals project for half an inch below the occipital foramen, to form the two stout occipital condyles, which have unfortunately been sawn through.
[128] I can find no indication of a suture in the bony plate which covers the supraoccipital region. The quadratum is cut away on one side, and so embedded in the matrix, on the other, that its form cannot be made out. The whole suspensorium, however, projects downwards and backwards. The lower jaw has the same parabolic outline as the skull; but some adherent matrix must be cleared away before its exact proportions and constituents can be made out. The teeth are very numerous, and close-set, not more than 1/8th of an inch long. They are conical, straight, and sharp-pointed; and their bases are expanded, and marked by about twelve longitudinal folds, which extend to near the apex of the tooth.
On comparing this fossil with Brachyops laticeps, its proportions are seen to be widely different, though the two skulls have within half an inch of the same length; and therefore specific identity is out of the question. Indeed, considering the additional difference in the relative size, in the form, the position, and the direction of the orbits, I conceive that the Australian fossil may be safely regarded as the type of a new genus, for which I propose the name of Bothriceps, in allusion to the peculiarly pitted character of the sculpture of such of the cranial bones as are left. I should, indeed, have been disposed to bring forward this pitted sculpture more prominently in alluding to the difference between this genus and Brachyops, were it not that the character of the surface of that part of the skull of the latter fossil which corresponds with all that is left of the cranial bones of Bothriceps is not clearly discernible. The present species may be called Bothriceps Australis.
Whatever be the relations between the Australian and Indian fossils, the evidence, as it stands at present, justifies our regarding both as generically distinct from the African Labyrinthodont, whose dermal scutes alone separate it from all other members of the group, the scutes of Archegosaurus having perfectly different characters.5
I propose therefore to form a new genus, Micropholis, for this African fossil, and to call it Micropholis Stowii, after its discoverer,6 who has the merit not only of finding the fossil, but recognizing its Batrachian affinities, sending home with it the skull of that African Frog which seemed to him most nearly to approach it.
The concurrence of Labyrinthodont remains with the beaked and [129] few-tootbed or toothless Dicynodont Reptiles7 in the Karoo-beds of Africa presents so striking a resemblance with the assemblage of Reptiles characteristic of the Fauna of the Trias in this country, that one is at first inclined to leap to the conclusion, that the discovery of this association settles the question of the age of the African formation. When I consider, however, that Labyrinthodont Amphibia range from the Lias down to the Carboniferous formations inclusive, and that Micropholis is not very closely allied to any of the more characteristic forms of the Trias, I am inclined to pause before drawing any very decided inference from the analogy of the Faunas.
DESCRIPTION OF PLATES XXI. AND XXII [PLATES 7, 8]
MICROPHOLIS STOWII
PLATE XXI. [PLATE 7].
Fig. 1. Skull of Micropholis Stowii, viewed from above. Magnified 2 diameters.
Fig. 2. The same, seen from the left side. Magnified 2 diameters.
Fig. 3. The same, seen from below. Magnified 2 diameters.
Fig. 4. The posterior end of the right ramus of the mandible,
and of the mandibular suspensorium of the same.
Fig. 5. Transverse section of the mandibular ramus.
Fig. 6. A portion of the mandible, with teeth in situ.
Fig. 7. The dermal scutes represented in fig. 3, magnified 10 times.
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BOTHRICEPS AUSTRALIS & DICYNODON MURRYI
PLATE XXII [PLATE 8].
Fig. 1. Dorsal or superior view of the cranium of Bothriceps Australis. Nat. size.
Fig. 2. Lateral view of the same, reduced to one-third diam.
Fig. 3. Transverse section of the snout of Dicynodon Murrayi, taken
perpendicularly to its axis, just in front of the internal nares.
Reduced to one-half diam.
Figs. 4, 5, 6. Similar sections, taken successively nearer the extremity of the snout.
Reduced to one-half diam.
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FOOTNOTES
1 Since this paper was read, I have published an account of the structure of the Labyrinthodont jaw to which reference is made, in Mr. Howell's "Memoir on the Warwickshire Coalfield": Memoirs of the Geological Survey, 1859.
2 I learn from Professor Ramsay that the stratum in which Dasyceps Bucklandi occurs is of Permian, not of Triassic age.
3 I therefore propose to change its name into Dasyceps Bucklandi, the generic appellation alluding to the singularly rough and prickly surface of the cranial bones, like that of some recent Bratrachia. (See Mr. Howell's Memoir cited above, in which the cranium of Dasyceps is described and figured.)
4 Quart. Journ. Geol. Soc., vol. x. p. 473; and vol. xi. p. 37
5 There is no certainty that the Anisopus scutulatus (Owen) of the Warwickshire Trias is really a Labyrinthodont; and if it proves to be such, its scutes are very different from those of Micropholis.
6 Quart. Journ. Geol. Soc., vol. xv. p. 193.
7 Mr. Stow collected in the same locality (at the foot of the Rhenosterberg), together with the Micropholis, some Dicynodont remains, to which I hope to return on a future occasion.
