Quarterly Journal of the Geological Society of London/Volume 26/On Hypsilophodon Foxii, a new Dinosaurian from the Wealden of the Isle of Wight

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3. On Hypsilophodon Foxii, a new Dinosaurian from the Wealden of the Isle of Wight. By T. H. Huxley, LL.D., F.R.S., President of the Society.

(Plates I. & II.)

During the meeting of the British Association at Norwich in 1868, Mr. F. Fellows, on behalf of the Rev. W. Fox, read a paper on, and exhibited the skull of, a fossil reptile discovered by that inde- fatigable explorer of the rocks of the Isle of Wight in a bed of the Wealden formation, "which forms the floor of Cowleaze Chine, and rises to the top of the sea cliff at Barne's High, in the parish of Brixton." Mr. Fox considered the reptile to be a "young Iguanodon" or more probably a "new small species of Iguanodon" and stated that he had found "several other skeletons" of the animal in the same locality.

In accordance with a wish expressed to me by Mr. Fellows, I made as careful an examination of the specimen as the circumstances would permit, and embodied the results of the investigation in some observations, accompanied by extemporaneous illustrations, which I made before Section C when the paper was read.

I pointed out the peculiar value of the skull, which arose from the nearly entire condition of the præmaxillary hones, which last had, up to that time, been displayed by no Dinosaurian fossil, except, perhaps, Compsognathus. I further drew attention to the singular fact that the incisor teeth, or those contained in the posterior moiety of each præmaxilla, were totally different in shape from the maxillary teeth; and that the anterior moiety of the præmaxilla was beak-like and edentulous. Moreover I expressed the opinion that while the affinity of the reptile with Iguanodon was clear, the extent of that affinity could only be determined by further critical comparisons.

I lost sight of the specimen for a long time; but, some months ago, hearing that it was in Mr. Fellows's keeping in London, I requested Mr. Pox's permission to subject it to more careful study. That permission was very readily and liberally accorded by Mr. Fox, and I now offer the results of this further work to the Society.

The skull (Pl. I. fig. 1), when entire and undistorted, must have had a length of rather less than four inches (probably about 3⋅8 or 3⋅9). The greater portion of the roof and of the right upper maxillary apparatus, with a part of the occipital surface, are displayed. The whole left nasal bone is exposed, together with part of the left præmaxilla and a portion of the left ramus of the mandible.

Two relatively large supratemporal fossæ, each about three-quarters of an inch long and four-tenths of an inch wide, lie at the sides of the parietal region, which is somewhat narrow in the middle, but expands at each end. The parietal bones (Pa) are a good deal injured, but they appear to have inclosed an oval median parietal foramen. In front, they unite by a transverse suture with the large frontal bones (Fr). Each of these is 1⋅4 inch long, 0⋅5 inch broad behind, and rather narrow in front, flattened though slightly concave from side to side, and somewhat convex from before backwards. The inner edges of the two frontal bones are a little raised where they unite in the frontal suture. The nasal bones (Na) are very large, being as long as the frontals, and very nearly as broad behind, where they are flattened and continue the direction of the roof of the skull. Anteriorly they narrow; and their outer surfaces, becoming convex, look somewhat outwards. Each nasal bone ends by a deeply concave rounded free margin, which bounds the nostril (N) above, and sends down a slender process on each side. The inner of these bounds the greater part of the inner side of the nostril, and lies upon, and internal to, the anterior ascending process of the præmaxillary bone (Pmx). The outer, in like manner, applies itself to the anterior edge of the ascending process of the maxillary, and forms a part of the outer boundary of the nostril.

The præmaxilla is a very large and remarkable bone. The body, or dentigerous portion, is 0⋅8 inch long and 0⋅3 inch high, from the alveolar edge to that which bounds the nostril below. The greater part of the outer surface of the bone is smooth; but towards its anterior end it becomes rugged and pitted, and seems to have been produced downwards and forwards into a short beak-like process. Upwards and backwards the same region of the præmaxilla passes into its anterior ascending process, which is 0⋅7 inch long, and becomes very slender above. Each uniting by harmonia, but not ankylosing, with its fellow, the two lie between, and separate, the inner edges of the nasal bones for a certain distance. Behind the nasal aperture the præmaxilla rises into its posterior process, which is about as long as the anterior, but has a much greater breadth. The posterior margin of the process, and of the body of the bone below it, is concave, rounded, and must have been quite loosely united with the anterior edge of the maxilla.

Five teeth with lanceolate acuminated crowns (fig. 3) lie close together in the præmaxilla, occupying a distance of 0⋅55 inch from its posterior end; but the alveolar margin of the "beak," which is continued in front of this, presents no indication of the presence of teeth. The maxilla is imperfect behind. So much of it as remains measures 1⋅5 inch in length, and rather more than half an inch in depth, posteriorly, where it is deepest. It bears ten teeth. The crowns of the anterior eight are well preserved; but the two hindermost are broken, only the section of the fang of the last being visible. The anterior four teeth are rather smaller than the others; and this is especially true of the first tooth. The anterior edge, of the crown of each of these teeth slightly overlaps the posterior edge of the crown of its predecessor. In the fifth, sixth, seventh, and eighth teeth, the overlap seems to have taken place in the opposite direction, the hinder edge of each tooth projecting a little beyond the anterior edge of its successor. The teeth are imbedded by single fangs, and, judging from the hindermost, are lodged in distinct alveoli. In unworn teeth the summit of the crown is sharp, and has a curved contour, which is more convex downwards in the anterior than in the posterior teeth. The free edge of the crown presents no trace of the serrations which are so characteristic of the teeth of Iguanodon; but it is sinuated by the terminations of sundry strong ridges of the enamel (fig. 2), which start from a sort of cingulum at the junction of the crown with the fang and, somewhat diverging and diminishing in thickness, traverse the outer surface of the crown. The cingulum is sharply angulated upwards in the three anterior teeth; but the angle becomes obtuse in the hinder teeth. The principal enamel ridge proceeds from the open angle of the cingulum, or a little behind it, to the crown. Secondary ridges of less prominence, which may not reach the cingulum, subdivide the spaces on each side of the principal ridge; and between them there are still shorter tertiary ridges, which do not extend more than halfway from the free edge towards the fang of the tooth. The sixth tooth is that the crown of which is most worn down, the other teeth being to all appearance less worn as they are further from it. The planes of the worn surface of the crowns, as in Iguanodon, cut the axis of the tooth at an acute angle, looking inwards as well as downwards. The outer contours of the teeth are convex from above downwards, but hardly so much so as in Iguanodon.

At first sight, these teeth look very similar to those of Iguanodon; and I was almost disposed to admit their identity with those of the latter genus, after the rapid examination which was alone possible at the meeting of the British Association at Norwich. A more critical comparison, however, has convinced me that the teeth of this reptile are perfectly distinct from those of the great Wealden Dinosaurian.

A large postfrontal separates the orbit from the temporal fossa, and appears to have united with the jugal, of which only an impression remains. A præfrontal is distinguishable at the upper and anterior part of the orbit. Beneath and behind it, lies a broken but very large and curiously curved lacrymal (La), which is deeply grooved upon its outer surface, the outer and posterior lip of the groove being much shorter than the inner and anterior lip. An ascending process of the maxilla seems to have articulated with the posterior and inferior end of the lacrymal. The anterior margin of this lacrymal process of the maxilla, the superior margin of the body of the maxilla in front of it, and the posterior margin of that broad nasal process of the maxilla which ascends behind the præmaxilla are all smooth, and evidently natural, free edges. Hence there must have been a considerable prælacrymal vacuity (a) in the walls of the face. The postfrontal sends a long process backwards, outside an anterior prolongation of the squamosal, the two combining to form the supratemporal zygoma. An impression on the matrix proves that there was a strong infratemporal zygoma formed by the jugal and quadrato-jugal; and on the left side the under part of this is visible. Remains of large sclerotic plates lie in the orbit. The hinder face of the distal half of the quadrate bone is displayed upon the left side (fig. 4, Qu). It is a very strong bone, the articular surface of the condyle measuring not less than half an inch from side to side.

The occipital face of the skull is much injured, but it was evidently directed almost perpendicularly to the upper face. The left parotic process is well displayed, and is proportionally large, being half an inch long and 0⋅3 inch wide. The base of the skull exhibits the injured basioccipital region, and the more perfect basisphenoid, which possesses two strong, divergent, basipterygoid processes. Against the outer ends of these the strong pterygoid bones abut. These are not at all unlike the corresponding bones in an Iguana. The central part, or body, of the bone is very strong; and it sends backwards and outwards a deep, laterally compressed plate, which abuts against the inner side of the quadrate bone. The body of the pterygoid bone is very strong, and produced vertically. Anteriorly and externally it becomes connected, by a transverse bone, with the maxilla. A small palatine bone is seen on the left side in front of the pterygoid. The pterygoid is, in many respects, like that bone in the existing Iguanæ; and this specimen shows very clearly that the Dinosauria had a Lacertilian and not a Crocodilian arrangement of the pterygoid and palatine bones. Only the right ramus of the mandible can be seen; and the symphysial end of that is broken away. But what remains is nearly in place, and shows that the angular process was relatively small, while the coronoid rises abruptly, in front of the articular surface, to the height of an inch from the inferior edge of the ramus. From the coronoid process, the height diminishes with a tolerably rapid sweep (but not so rapid as in Iguanodon), and the broken end, 2⋅5 inches from the articular surface, is only 0⋅5 inch high. The mandibular teeth are completely hidden.

The centrum of a vertebra (fig. 1, c), which lies on the outer side of the ramus of the mandible, is 0⋅6 inch long, and the exposed articular end, which is very slightly concave, is 0⋅45 inch high by 0⋅4 inch wide. The middle of the centrum is narrower than the ends, and the whole centrum, seen sideways, looks remarkably flat and wall-sided. Any processes the vertebra possessed must have come off from the neural arch, and therefore there can be no doubt that this is a dorsal vertebra. Thus the length of the skull appears to have equalled that of about six dorsal vertebræ.

The teeth of this reptile leave no doubt as to its distinctness from Iguanodon; and, as I shall immediately bring forward evidence to prove, that difference is generic. I propose, therefore, to name it Hypsilophodon[1] Foxii.

In the British Museum there is a considerable portion of the skeleton of a reptile, imbedded in the two portions of a slab of Wealden sandstone, of which the one was formerly the property of Dr. Mantell and the other of Dr. Bowerbank, but which are now happily reunited. This skeleton has been described and figured by Professor Owen, in the publications of the Palæontographical Society, as that of a young Iguanodon Mantelli.

The fossil is stated to have been discovered "in the Wealden formation, about one hundred yards west of Cowleaze Chine, on the north-west coast of the Isle of Wight, in the year 1849;" and the Rev. Mr. Fox informs me that it was found in the same bed as his specimen of Hypsilophodon, a stratum which, up to the present time, has yielded no remains of Iguanodon.

Two years ago, namely in December 1867, I became convinced, by the evidence of the British-Museum specimen itself, that it could not possibly be Iguanodon. The form and proportions of the vertebræ, especially of the caudal vertebræ, were quite different; the femur, with many points of similarity, exhibited sundry remarkable differences; and, most important of all, the metatarsus proved the Cowleaze reptile to have, at fewest, four well-developed toes. Again, if, as the describer of the fossil imagined, the bones numbered 66 and 67 (Palæontographical Society, "Fossil Reptilia of the Wealden," tab. i.) are the right tibia and fibula, any identification with Iguanodon is out of the question, inasmuch as the leg would be much longer than the femur, while in Iguanodon, as the Maidstone specimen proves, it is shorter. Thus I made sure that the Cowleaze fossil represented a new genus; and, under the circumstances, the probability that it once formed part of the body of a Hypsilophodon is obviously very great. The fortunate preservation of the centrum of a single dorsal vertebra, along with the skull, greatly strengthens this already strong presumption. On comparisonson with a vertebra from the anterior dorsal region of the specimen in the British Museum, I can find absolutely no difference, except that the vertebra in Mr. Fox's specimen is a shade smaller. The centra of the anterior dorsals in the former are rather less than 0⋅7 inch long; in the latter the measurement is 0⋅63 inch. The difference, therefore, is not more than 1/20 of an inch. The vertebral column of the specimen in the British Museum has been particularly described by Professor Owen; but the caudal vertebræ have been much more completely cleared of the matrix since his memoir was written. The remains of eighteen vertebræ may be made out, in consecutive series, from the cervical to the posterior dorsal region; and the position of the ilium is such, that there can hardly have been more than two or three vertebræ between the hindermost of those which are visible and the sacrum. In the most anterior of these eighteen vertebræ (which may thus, probably, be the twentieth, or twenty-first., from the sacrum) the anterior, escutcheon-shaped, face of the centrum is distinctly convex from side to side, and slightly concave from above downwards, while the posterior face is markedly concave. The neuro-central suture passes through the capitular process; and the tubercular process springs much higher up upon the arch, beneath the præzygapophysis, the articular face of which looks as much inwards as upwards[2]. It is only the hindermost, or ninth, cervical vertebra of a crocodile which presents these characters. In all the more anterior cervicals the neuro-central suture passes above the process for the capitulum of the rib; I therefore conclude that, in all probability, the anterior vertebra of the Hypsilophodon skeleton belonged to the posterior region of the neck. I should think it very possible that there may have been seven, or eight, cervical vertebræ between the most anterior of those preserved and the head. In this case, the light head, borne upon the relatively long neck, will have given the fore quarters of Hypsilophodon much resemblance to those of a Monitor.

Professor Owen concludes, from certain striæ on the articular surfaces of the vertebral centra, that "the vertebral bodies of the Iguanodon were coarticulated by means of an intervertebral ligament, as in the class Mammalia;" and he emphasizes this conclusion by putting it in italics. I have little doubt that the vertebral centra of Hypsilophodon were so connected; but so are those of a Crocodile, and the fact does not constitute the slightest evidence in favour of the mammalian affinities of the Dinosauria.

In resuming my study of the specimen of Hypsilophodon in the British Museum, for the purposes of the present paper, the difficulty which had previously presented itself of reconciling what could be seen of the structure of the bones numbered 66 and 67 (tab. i. 'Fossil Reptilia of the Wealden Formation') with what is known of the tibia and fibula of the Dinosauria returned very strongly to my mind. On the other hand, my present knowledge of the strange characters of the pelvis in the Dinosaurian reptiles led me to suspect that those bones might prove to be the pubis and ischium in situ, and in their natural connexion with the right ilium, the posterior part of which bone (numbered 62 in the plate cited) was conspicuously visible. Careful search revealed the anterior end of the bone overlying the arch of the posterior vertebræ of the dorsal series.

With the permission of the Keeper of the fossil collection, therefore, the specimen was subjected to a further careful removal of the matrix in the requisite directions. The result has been the complete verification of my conjecture, and the specimen now affords a view of the ventral elements of the pelvis in their natural relations (Pl. II.).

The middle part of the right ilium is covered, and, seemingly, a little crushed in, by the left foot. But its broad postacetabular portion (b), and its relatively narrow and pointed præacetabular part (a) are completely exposed. I suspect that the ilium is broken in the middle, and, as a consequence, that the distance from the posterior to the anterior ends of the visible parts of the bone (6⋅6 inch) is somewhat greater than it should be. Hence the acetabulum probably appears to be longer than it naturally is. The postacetabular process (c), which should articulate with the ischium, is swollen and thick, but thins off, above and behind, into a thin vertical plate, the posterior curved margin of which is broad and turned in, like a narrow shelf. The præacetabular prolongation is slender, and its broken narrow end (a) rests on the arch of the seventeenth vertebra.

The anterior boundary of the acetabulum is formed by a broad, somewhat flattened, facet of bone (d), which looks backwards and a little outwards. The osseous mass, of which this forms the posterior aspect, rapidly narrows forwards, and is prolonged above into a slender ridge, or process, with a free rounded end (a). In front, it has a sinuated free edge; anteriorly and below, it is continued into a slender rod-like pubis (Pb), between six and seven inches long, which passes downwards and backwards parallel with the ischium. On the outer surface, in front of the lower part of the articular surface, lies an oval foramen (e). The posterior edge of the bone is concave and free. Posteriorly and below, it ends in a broad thin prolongation, which passes backwards, internal to the ischium. The part of the bone which bears the facet answers very well to the præacetabular process of the ilium of Megalosaurus and of Thecodontosaurus. The perforation is indeed somewhat like that which is so generally found in the pubis of Lizards; but, on a future occasion, I hope to be able to show its analogue in the ilium of an undoubted Dinosaurian. If this part of the acetabular wall answers, as I believe it does, to the descending præacetabular process of the ilium, all trace of the suture between it and the pubis has disappeared.

The right ischium (Is) lies in undisturbed relation with the pubis. Its acetabular end has a free superior concave edge which bounds the acetabulum below, a broad thin anterior process which overlaps and is firmly united with the pubis, and a posterior process which becomes very thick behind and articulated with the postacetabular process of the ilium. The shaft of the bone is flattened laterally, and has a thick and rounded posterior edge. Anteriorly it is thinner, and at 2⋅75 inch from the acetabulum it is produced into a broad and long decurrent process, the free edge of which overlaps the pubis. Such a process is very generally developed in birds. Beyond this process the ischium widens out, and seems to terminate in a spatulate free end, like that of the corresponding part of the ischium in Megalosaurus and Iguanodon. This spatulate extremity is broken away from the right ischium, but remains on the other side (Is'). And their relative position leads to the belief that the two bones united in a ventral symphysis. The long diameters of the ischia and pubes are parallel, and they are directed downwards and backwards in such a manner as to make an obtuse angle with the anterior half of the long diameter of the ilium. Hypsilophodon is the first reptile in which this disposition of the ischium and pubis has been observed.

Eleven caudal vertebræ in series, with a rudiment of a twelfth at the posterior end, and another which lies on one side of these, all belonging to the anterior part of the tail, are represented in the plate cited, but they have been worked out much further since it was published. The characters of some of the vertebræ are very well shown. For example, the third from the anterior end in the series of eleven now exposed, is 2 inches high from the lower edge of the centrum to the summit of the spine (Pl. I. figs. 6 & 7). The centrum is 0⋅8 inch long, while its articular faces are 0⋅6 inch high. The transverse measurements of the articular faces of the centrum cannot be ascertained in this vertebra; but that of the posterior face of the vertebra which lies by itself is 0⋅5, the length of the vertebra being 0⋅7 inch. The spine of the "third" vertebra measures, from the postzygapophysis to its truncated extremity, 0⋅85 inch, and 0⋅36 inch from before backwards; the spines of all the caudal vertebræ are slightly inclined backwards. The root of a transverse process (or caudal rib), 0⋅36 inch long, stands out at right angles from the upper part of the side of the centrum, its posterior edge inclining forwards. The under face of the centrum is concave from before backwards, and presents a narrow and flattened surface, traversed by a longitudinal groove. The zygapophyses are long, and the planes of their articular faces are almost vertical. The obliquely truncated surfaces for the articulation of the chevron bones at the anterior and posterior ends of the ventral face of each centrum are well marked. No chevron bone is attached to the vertebra under consideration; but several lie, one on the top of the other, beneath the fifth to the eighth vertebra of the caudal series. The best-preserved of these is 1⋅75 inch long, 0⋅38 inch wide at the vertebral end (Pl. I. fig. 8) . The vertebral ends of the forks of the chevron bones are expanded and ankylosed together in the manner characteristic of the Dinosauria.

The length of the left femur is 5⋅7 inches, or rather less than the length of the hinder eight of the series of dorsal vertebræ. The extreme breadth of the distal end is 1⋅45 inch, the extreme breadth of the proximal end, from the inner surface of the articular head to the outer surface of the shaft, 1⋅73 inch. The femur is therefore slightly shorter in proportion to the length of the dorsal vertebræ than in Iguanodon. The faces of the inner trochanter look much more directly inwards and outwards, and the whole process has a different shape from that of Iguanodon. There is no pit above the inner trochanter, such as exists in Iguanodon; and the deep intercondyloid groove, on the anterior face of the distal end, which is so characteristic of Iguanodon, is wanting.

The remains of what I take to be the right fibula and tibia are seen in front of the pelvis. What remains of the fibula is 4 inches long, and shows the proximal end and moiety of the shaft tolerably entire. The former measures 0⋅7 inch from before backwards, but not more than 0⋅2 inch in width. The anterior edge of the shaft is turned towards the eye. An impression on the matrix is continued in the line of direction of the bone, and suggests that it was altogether about five inches long, and that its distal end had a width of 0⋅4 inch. In Iguanodon, the length of the tibia is to that of the femur as 31 to 33, and the fibula is somewhat shorter than the tibia. If Hypsilophodon followed the proportion of Iguanodon, the tibia should be 5⋅35 inches long, and the fibula rather more than five inches.

On reference to the memoir which I have cited, it will be observed that my interpretation of the bones described is very different from that adopted by Prof. Owen (p. 2). He terms the femur (65) "the right femur," and states that "the bones of the right hind leg are almost completed when the blocks containing their opposite ends are brought into juxtaposition." But the most cursory inspection is sufficient to show that the femur belongs to the left side, and, as I have proved, the so-called right tibia and fibula (66 and 67) are really the two ischia and the pubes.

I find myself compelled to dissent as widely from Prof. Owen's view of what he terms "the principal bones of the right hind foot." I have no sort of doubt it is the left hind foot. For there are two bones belonging to the distal tarsal series in their natural relation with one another, and with two, if not three, metatarsal bones. These bones are obviously the homologues of those which exist in Scelidosaurus and in the Crocodilia, and which lie on the outer side of the foot. The metatarsals which are connected with these bones, therefore, must needs belong to the outer, or fibular, digits; and, as the dorsal surface of the metatarsus is turned towards the eye, the foot can only be that of the left limb. In the proximal row of the tarsus lie a calcaneum (which seems to have a process as in Crocodiles) and an astragalus, with a convex distal face and seemingly flattened from above downwards. "Whether it has an ascending process cannot be distinctly made out. The proximal and the distal series of bones are dislocated, and what looks like the end of the tibia is seen between and below them. The metatarsals of the first, second, and third digits are quite distinct; but the distal end is entire only in the first, or that of the hallux, which measures 1⋅85 inch in length. It has a pulley-shaped articular surface, and is 0⋅5 inch wide. The shaft of the bone is greatly compressed from side to side, as in Scelidosaurus. The second and third metatarsals are much broader and stouter, with flattened superior faces. They also seem to have been longer than the first. The fourth metatarsal looks, at first, as if it were much wider than the other; but, on close examination, I think I can trace a line of matrix separating a true fourth metatarsal, of about the same size as the others, from a slender fifth metatarsal. A basal phalanx, which seems to have belonged to the middle digit, is 1 inch long, 0⋅6 inch wide at the proximal, and 0⋅35 inch at the distal end. The pes of Hypsilophodon, thus, was either tetradactyle or pentadactyle.

The length of the trunk and tail of Hypsilophodon was probably about 41/2 feet; and, in all likelihood, it was mainly herbivorous.

[For description of Plates I. & II. see p. 50.]

Plate I.

Fig. 1.

The skull of Hypsilophodon Foxii, of the natural size. Pa, parietal; Fr, frontal; Na, nasal; Pmx, præmaxilla; La, lacrymal; Mn, mandible; a, prælacrymal vacuity; b, suture between the præmaxillary and maxillary bones; N, nasal aperture; c, centrum of a vertebra.

2.

A molar tooth, and

3.

An incisor tooth, magnified.

4.

The left ramus of the mandible: Qu, the quadrate bone; a, the coronoid process.

5.

The left præmaxilla. In this figure and in fig. 1. the line from Pmx leads to the edentulous prolongation.

6.

Side view of a caudal vertebra, of the size of nature.

7.

End view of another caudal vertebra.

8.

A chevron bone, of the natural size.

Plate II.

The pelvis of Hypsilophodon Foxii, two-thirds the natural size. a, the anterior, b. the posterior extremity of the right ilium; Is. Is. the right and left ischia; Pb. the pubis.


E. Fielding
M. & N. Hanhart imp.
 

HYPSILOPHODON FOXII

E. Fielding
M. & N. Hanhart imp.
 

HYPSILOPHODON FOXII
  1. Hypsilophus is a name proposed by Fitzinger for certain Iguanas.
  2. The two following vertebræ have similar characters; but the articular surface of the sixth appears to be slightly concave in front as well as behind. In this vertebra the transverse process springs from the arch, far above the neuro-central suture.