CHAPTER XVII.

FOSSIL REPTILES; COMPRISING THE DEINOSAURIANS, PTERODACTYLES, TURTLES, SERPENTS, AND BATRACHIANS.

III. Deinosaurians.--The Order Deinosauria (_fearfully-great lizards_) has been established for the reception of those extinct colossal reptiles, comprising the _Megalosaurus_, _Hylæosaurus_, _Iguanodon_, and _Pelorosaurus_, which, in their organization, present the transition from the Crocodilians to the Lacertians, and whose essential osteological characters Professor Owen has described as follow:--

"This group, which includes at least three well-established genera of Saurians, is characterized by a large sacrum, composed of five anchylosed vertebræ of unusual construction; by the height, breadth, and outward sculpture of the neural arch of the dorsal vertebræ; by the two-fold articulation of the ribs to the vertebra:, viz. at the anterior part of the spine by a head and tubercle, and along the rest of the trunk by a tubercle attached to the transverse process only; by broad, and sometimes complicated, coracoids, and long and slender clavicles; whereby Crocodilian characters of the vertebral column are combined with a Lacertian type of the pectoral arch. The dental organs also exhibit the same transitional or annectent characters, in a greater or lesser degree. The bones of the extremities are of large proportional size for Saurians; they are provided with large medullary cavities, and with well developed and unusual processes, and are terminated by metacarpal, metatarsal, and phalangeal bones, which, with the exception of the ungual phalanges, more or less resemble those of the heavy pachydermal Mammals, and attest, with the hollow long-bones, the terrestrial habits of the species.

"The combinations of such characters, some, as the sacral ones, altogether peculiar among Reptiles, others borrowed, as it were, from groups now distinct from each other, and all manifested by creatures far surpassing in size the largest of existing reptiles, will, it is presumed, be deemed sufficient ground for establishing a distinct tribe or sub-order of Saurian Reptiles, for which I would propose the name of Dinosauria.

"Of this tribe the principal and best established genera are the _Megalosaurus_, the _Hylæosaurus_, and the _Iguanodon_; the gigantic Crocodile-lizards of the dry land; the peculiarities of the osteological structure of which distinguish them as clearly from the modern terrestrial and amphibious Sauria, as the opposite modifications for an aquatic life characterize the extinct _Enaliosauria_, or Marine Lizards."[626]

[626] Brit. Assoc. Rep. 1841, p. 103.

The elaborate investigation of the fossil remains of these stupendous beings, and the luminous exposition of their organization and physiological relations, embodied in the report to which the above extract is introductory, are among the most important contributions to Palæontology, and afford a striking example of the successful application of profound anatomical knowledge to the elucidation of the most marvellous epoch in the earth’s physical history, the _Age of Reptiles_.

From the great size of the bones of these reptiles, their remains have excited the curiosity even of the common observer; and although an exaggerated idea has been generally entertained of the magnitude of the original animals, yet, even when reduced to their natural proportions by the rigorous formula of the anatomist, applied to the accumulated relics which years of laborious research have exhumed from their rocky sepulchres and deposited in our museums, their dimensions are sufficiently stupendous to satisfy the most enthusiastic lover of the marvellous.

Let the reader visit the British Museum,[627] and after examining the largest thigh-bone of the Iguanodon, repair to the zoological gallery, and inspect the recent Crocodilian reptiles, some twenty-five or thirty feet in length; and observe that the fossil _bone_ equals, if not surpasses, in size, the entire _thigh_ of the largest of existing reptiles; then let him imagine this bone clothed with proportionate muscles and integuments, and reflect upon the enormous trunk which such limbs must have been destined to move and to sustain--and he will obtain a just notion of the appalling magnitude of the lizards which inhabited the country of the Iguanodon.

[627] See Fossils of the British Museum, p. 227.

The general characters of the extinct reptiles comprised in the order _Deinosauria_[628] must be known to the intelligent reader, from the various popular notices which have from time to time appeared; and their names have become as familiar as household words. I shall here restrict myself to a few general remarks on the form and structure of the teeth, and of some of the more important bones of the best known species of these great reptiles.[629]

[628] In the new edition of Pictet’s _Paléontologie_ (now in course of publication), two 4to. plates (xxiii. and xxiv.) are devoted to the illustration of the remains of these colossal reptiles.

[629] For further account of the Iguanodon, see _Petrif._ p. 224, &c.; of the Hylæosaurus, _ibid._ p. 314, &c.; of the Pelorosaurus, _ibid._ p. 330, &c.; of the Regnosaurus, _ibid._ p. 333, &c.; and of the Megalosaurus, _ibid._ p. 328, &c.

[Sidenote: MEGALOSAURUS.]

Megalosaurus (_gigantic lizard_) Bucklandi. _Lign._ 218 and 219. _Bd._ pl. xxiii. _Wond._ p 421.--The oolitic flag-stone of Stonesfield, in Oxfordshire, has long been celebrated for the bones and teeth of a gigantic reptile, which Dr. Buckland first described by the name of _Megalosaurus_, in a highly interesting memoir (_Trans. Geol. Soc._ _sec. ser._ vol. i.), illustrated by figures of the teeth in a portion of the lower jaw, the sacrum, femur, and other bones. The remains of this reptile are also frequently discovered in the Wealden (see _Foss. Til. For._ p. 67, pl. ix. figs. 2, 6). The most important relic of this great carnivorous terrestrial lizard is a portion of the right ramus of the lower jaw, containing one perfect tooth, and the germs of several teeth (_Lign. 218_). The tooth of the Megalosaurus, (_Lign. 219_, and _Pl. VI. fig. 7_,) has a conical, laterally compressed crown, with the point recurved like a sabre, and the edges trenchant and finely serrated. The implantation of the teeth is very peculiar, and exhibits the dentition of the Crocodilians blended with that of the Lacertians. The jaw has an outer parapet, as in the true lizards (see _Lign. 205_), but the teeth are fixed in distinct sockets, formed by transverse partitions, that are attached to a mesial (_inner_) parapet, composed of a series of triangular osseous plates; the bases of the old teeth, and the germs of the new ones, being thus enclosed and concealed. The tooth is formed of a central body of dentine, the crown having a coating enamel; and the whole an external investment of cement, which forms a thicker layer around the fang; the pulp-cavity is occupied by coarse bone, in the adult tooth. The microscopical examination shows the dentine to consist of very fine calcigerous tubes, 1/28000th of an inch in diameter, without any admixture of medullary canals, radiating from the pulp-cavity at right angles with the external surface of the tooth, and sending; off numerous secondary branches; these ultimately dilate into, or inosculate with, a stratum of calcigerous cells that separates the dentine from the enamel.[630] A thin slice of a vertical section, viewed by transmitted light, is represented _Pl. VI. fig. 7 b_; showing the calcigerous tubes radiating from the centre, and terminating in the stratum of cells; this cellular structure is invested with a layer of enamel, and the latter with an external coat of cement, indicated by the dark outline.[631]

[630] Owen’s _Odontography_, p. 271, which should be consulted for more minute details.

[631] To fully comprehend the minute structure of these and the other teeth figured in _Pl. VI._ Professor Owen’s plates should be examined; the small scale necessarily adopted in the present work rendering it impossible to do justice to the subject.

Four specimens of the sacrum, composed of five anchylosed vertebral (_Foss. Til. For._ pl. xix. _fig._ 12), have been discovered; one of these is from Tilgate Forest. The femur of the Megalosaurus has two large rounded trochanters of nearly equal size, below the head of the bone; its shaft is sub-cylindrical, and slightly bowed.

This colossal carnivorous Saurian, whose length is estimated at thirty feet, appears to have been terrestrial, and an inhabitant of the same _terra incognita_ as the Iguanodon; it probably preyed on the smaller reptiles, and the young of the Iguanodon, Crocodilians, &c.

Hylæosaurus (_Wealden lizard_) Owenii. _Wond._ pl. iv. and p. 435; _Geol. S. E._ pl. v.--In the summer of 1832, I obtained the interesting specimen which first demonstrated the existence of the remains of another extraordinary modification of Saurian organization in the Wealden. The circumstances which led to this discovery afford an instructive lesson to the young collector.

Upon visiting a quarry in Tilgate Forest, which had yielded many organic remains, I perceived in some fragments of a large mass of stone, which had recently been broken up and thrown on the road-side, traces of numerous pieces of bone. I therefore collected all the recognisable portions of the block, and had them conveyed to my residence. The first step was to cement together those pieces that would admit of juxtaposition, and these were at length united into a block of stone five feet long, three wide, and about one foot thick. This was firmly fixed in a stout frame, to prevent the separation of the united portions during the process of chiselling. Guided by the indications which the sections visible on the edge afforded, a thin iron wedge was carefully driven in, about half an inch above the uppermost layer of bones, and a large slab was flaked off; the three dermal spines (_Wond._ pl. iv. 5) in the middle of the specimen were thus exposed, and shivered to pieces; some fragments adhered to the mass broken off, others to the block, and many were detached; every piece, however small, was collected, and those adhering to the slab were chiselled out; and the whole were then carefully replaced and cemented to the bones that remained imbedded in the large block. After an interval of some days, to allow of the firm cohesion of the cemented parts, the task was resumed, and the stone chiselled away, until some portion of the large bones of the pectoral arch (_Wond._ pl. iv. 7) were observed. The specimen was at length brought to the state in which it now appears (in the British Museum[632]); but during the progress of its development, which occupied many weeks, it was repeatedly necessary to suspend the work, and unite displaced fragments of bone, and resume the task after their consolidation. The plate in the _Geol. S. E._ conveys a good idea of the original.

[632] See _Fossils, Brit. Mus._ p. 139, &c.

The specimen consists of a part of the spinal column, composed of seven dorsal and three or four cervical vertebræ, almost in their natural juxtaposition, with obscure indications of a part of the base of the skull; eleven ribs; the bones of the pectoral arch (two _coracoids_ and two _scapulæ_); with numerous dermal bones and spines. A second specimen of this reptile was found near Bolney, in Sussex; and like the former, it was, unfortunately, almost wholly destroyed by the labourers; but I obtained many bones, some of which are perfect, and indicate an animal of considerable magnitude: a _scapula_, nineteen inches long, an arm-bone or _humerus_, numerous ribs, bones of the phalanges, &c. A fine series of twenty-six caudal vertebra, having a total length of nearly six feet, with chevron bones and dermal spines, was discovered in 1837, in Tilgate Forest.[633] A few detached bones are the only other relics of this reptile that have come under my observation.[634] The osteological characters presented by these remains afford another example of tire blending of the Crocodilian with the Lacertian type of structure; for we have in the pectoral arch the scapula or omoplate of a crocodile associated with the coracoid of a lizard. Another remarkable feature in these fossils is the presence of the large angular bones or spines (described p. 660, figured _Lign. 208_), which, there is reason to infer, constituted a serrated crest along the middle of the back: and the numerous small oval dermal bones, which appear to have been arranged in longitudinal series along each side of the dorsal fringe. (_Geol. S. E._ p. 323.)

[633] See _Fossils, Brit. Mus._ p. 323.

[634] See "Memoir on the Remains of the Iguanodon, Hylæosaurus, and other Saurian Reptiles," by the Author, in _Philosophical Transactions_ for 1841, Part II.

The vertebræ, ribs, and other parts of the skeleton found in these specimens also present modifications of structure of great interest.[635] No specimens of teeth have been found associated with the remains of the Hylæosaurus, in such manner as to afford unequivocal proof of their belonging to that animal. But in the same quarries, teeth, decidedly of the Lacertian structure, are occasionally found, and may with some probability be referred to that reptile. These teeth (see _Pl. VI. fig. 6^a_.) are about 1-1/4 inch in length, and commence at the base with a cylindrical shank, which gradually enlarges into a crown of an obtuse lanceolate form, convex in front, hollowed behind, and terminating in a rounded obtusely angular apex, the margins of which are generally more or less worn.[636] The crown is solid, but the fang encloses a small pulp-cavity; the surface is enamelled, and covered with very fine longitudinal striæ; the base in every specimen appears broken transversely, as if it had been anchylosed to the jaw, or to the base of a socket. The fang never presents an appearance of lateral adhesion, as if belonging to a Pleurodont lizard. Sections of these teeth expose a simple, central, medullary canal, the upper part of which is generally filled with the ossified remains of the pulp; and this is surrounded by a body of firm dentine, with extremely minute calcigerous tubes radiating from the centre to the periphery of the tooth, which is invested with a relatively thick coat of enamel, in which no structure is apparent. _Pl. VI. fig. 6^b_ represents a small portion of a vertical slice, highly magnified and viewed by transmitted light. The reference of these dental organs to the Hylæosaurus must not, however, be considered as conclusive, until confirmed by the discovery of the teeth attached to the jaw, in connexion with other parts of the skeleton. The locomotive organs of the Hylæosaurus are but imperfectly known; a perfect humerus, one phalangeal bone, and fragments of the fibula (the small bone of the leg) are the only bones hitherto observed. The length of this reptile, which was probably terrestrial and herbivorous, may be estimated at from twenty to thirty feet.

[635] See Report, Brit. Assoc. 1841, pp. 111-120. Phil. Trans. 1841, pp. 141-144, pl. x.

[636] Rep. Brit. Assoc. 1841, p. 118. Geol. S. E. England, pl. ii. figs. 2, 4. Phil. Trans. 1841, p. 144, pl. vi. figs. 9, 10, 11.

Iguanodon. _Ligns._ 219 to 226; _Wond._ pl. ii. iii., and pp. 422, &c.--Soon after my first discovery of the remains of vertebrated animals in the strata of Tilgate Forest, some teeth of a very remarkable character particularly engaged my attention, from their dissimilarity to any that had previously come under my notice.[637] Attention having been directed to these interesting fossils, examples were soon discovered of teeth in various conditions, from the sharp, unused tooth of the young reptile, to the obtuse, worn-out crown of the adult. From the resemblance of the perfect teeth to those of the Iguana (_Lign. 205_, p. 649), a land lizard of the West Indies, I proposed the name of _Iguanodon_ (signifying an animal with teeth like those of the Iguana) for the extinct reptile to which they belonged. The numerous bones and teeth subsequently exhumed from the strata of Tilgate Forest and other localities in the Wealden of Sussex and of the Isle of Wight, and the considerable portion of the skeleton of an individual discovered by Mr. Bensted in the Kentish Rag, have supplied the data upon which our present knowledge of the characters of the original is based.

[637] These are described in _Foss. South D._ 1822, p. 54, under the head "_Teeth and bones of unknown animals_." This was the earliest published notice of the fossils of the Wealden; it contains also a description of a tooth of the Megalosaurus (p. 55, No. 42).

In Wond, pp. 422-435, a brief account will be found of the character of the teeth, horn, femur, vertebræ, &c., and of the Maidstone specimen[638] (_Pl. III._).

[638] In a Monograph on the Reptiles of the Cretaceous Deposits of England, published by the Palæontographical Society, Professor Owen has lately figured anew and described in detail this most valuable fossil skeleton; to which description are appended the Professor’s latest views on the structure of the teeth of this reptile.

The "Geology of the South-east of England" contains accurate figures of the long bones of the leg (_Geol. S. E._ pl. ii), femur, clavicles (_Geol. S. E._ pl. iv.), tympanic bone (_Geol. S. E._ pl. ii.), horn and ungual bone (_Geol. S. E._ pl. iii.). In the "Fossils of Tilgate Forest," there are fifteen quarto plates devoted to the illustration of the bones and teeth of the Iguanodon and other Wealden reptiles. The osteological structure is fully detailed in _Rep. Brit. Assoc._ 1841, pp. 120-144. A general notice of the principal bones of the Iguanodon, with plates, will be found in _Phil. Trans._ 1841, pp. 131-151; and in _Petrif._ chap. iii. the author has given a detailed account of the most important specimens, both in the British Museum and in his own collection, together with a résumé of the palæontology and geology of the Wealden district.

Fig. 1.--The inner aspect, showing three teeth, and the sockets of eighteen. _a._ Germ of a tooth. _b._ Perfect crown of a successional tooth. _c._ Remains of a successional tooth, the upper part having been broken off. _d._ The symphysial extremity of the jaw. _e._ The opercular furrow. _f._ The coronoid process.

2, 3, and 4, the teeth _a_, _b_, and _c_, in _fig._ 1, represented on a larger scale.

[639] For the outer aspect, and a restoration of the whole jaw, _Petrif._ pp. 247 and 249.

Jaw and Teeth of the Iguanodon. _Ligns. 219-223._--Although the form and structure of the cranium are unknown, yet the half of a lower jaw, discovered in Sussex by Capt. L. Brickenden,[640] and a fragment of an upper jaw, found some years since,[641] enable us to form a tolerably perfect idea of the structure and functions of the dental organs of the Iguanodon. The unused tooth of this reptile is characterized by the prismatic form of the crown, the presence of from two to four longitudinal ridges on its enamelled face, the denticulated margins (_Lign. 221, a_), and finely serrated edge of the summit, as seen in _Lign. 220, fig. 3_. The shank or fang of the tooth (_Ligns. 221, 223, fig. 2_) is sub-cylindrical, slightly curved, and tapers to a point. The inner surface of the crown in the lower teeth, and the outer surface in the upper, are covered with a thick layer of enamel, but the opposite face of the crown and the sides have but a thin coating of this substance. The teeth of the upper jaw (_Lign. 222_) are curved in the opposite direction to those of the lower, and have the convexity external, and the concavity internal. Thus the upper and lower molars were related to each other nearly as in the Ruminants; the outer aspect below corresponding to the inner above (see _Petrif._ _Lign._ 56, p. 254). The specimens met with have almost always the apex of the crown more or less worn down by use[642] (see _Lign. 223_), and presenting an oblique, triangular, smooth surface, as in the fine large specimen figured in _Lign. 221_, which was found imbedded in the trunk of a Clathraria, as if it had snapped off while the animal was in the act of gnawing the tough stem. The denticulated margins are well developed; in _fig. 1_, they appear as simple serrations; but viewed laterally, they are seen to be formed by a series of denticulated plates (_Lign. 223, fig. 6_). The crown of a tooth of a young animal, worn at the summit, and presenting but three longitudinal ridges, is represented _Pl. VI. fig. 4^a_. The microscropical structure consists of a simple pulp-cavity in the centre of a body of dentine permeated by calcigerous tubes, but with this peculiar modification, that the dentine is traversed by vascular canals, radiating at definite intervals from the pulp-cavity nearly to the periphery of the tooth, and running parallel with the calcigerous tubes; thus constituting a softer and coarser dentine than in the other reptiles, and resembling that which characterizes the teeth of some of the herbivorous mammals.[643] The crown of the tooth is covered with a layer of enamel, which is thickest on the external surface: and the fang is invested with cement. The structure here described is shown in _Pl. VI.; fig. 4^b_, a vertical, and _fig. 4^c_, a transverse section of a tooth, seen by transmitted light, with a high magnifying power. The calcigerous tubes are 1/25000 an inch in diameter. Sections of the teeth of the Iguanodon are beautiful objects under the microscope, for the medullary canals are generally of a deep yellowish brown colour.

[640] Figured and described in the _Phil. Trans._ 1848, p. 188, pl. xvi. xvii.

[641] Both specimens are fully described in _Petrif._ pp. 242, _et seq._

[642] Plates iv. and xvii. in the "Fossils of Tilgate Forest," contain representations of upwards of thirty specimens of teeth in various states of development and detrition.

[643] Tomes on the Microscopic Structure of the Tooth of the Iguanodon, _Petrif._ pp. 239, 240. See also Owen’s _Odontography_, p. 249, and pl. lxxi.; and _Cycl. Anat._ Art. Teeth.

Fig. 1.--Outer aspect of an upper tooth (in a reversed position), worn flat, and with the fang absorbed; fig. 3, inner aspect of the same tooth. _a, a._ Flat grinding surface, produced by mastication when all the thickly enamelled portion of the crown is worn away. _c._ Cavity produced by the pressure of a new tooth. 2.--Lower tooth of a young animal, slightly worn: inner aspect. 4.--Outer Surface of a lower tooth of an adult; and fig. 5, inner surface of the same. _a, a._ The hard cutting edge of the oblique surface worn by mastication. _c._ Indentation produced by the pressure of a successional tooth. 6.--Edge view of the serration on fig. 5; magnified.

The dentine is less vascular, and therefore hardest, on that side of the crown which has the thicker coat of enamel; hence the tooth wears away faster on one side than on the other, and an oblique grinding surface, with a sharp edge of enamel, is maintained until the crown is worn away. The internal structure of the teeth of the Iguanodon is thus in perfect accordance with their external configuration, and must have been admirably adapted, in every stage, for the laceration and comminution of the tough vegetable substances which, there is every reason to conclude, constituted the food of this colossal oviparous quadruped.

Vertebra of the Iguanodon,[644] _Lign. 206_, p. 653; _Lign. 224_.--The remains of the vertebral column of the Iguanodon, consisting generally of broken and water-worn dorsal and caudal vertebræ, deprived of their processes and reduced to the state of the specimens represented _Lign. 206_, _figs._ 6 and 8, are so abundant in some of the Wealden strata, that a short account of their characters may be useful. A reference to _Lign. 206_, and its description, will render the following remarks intelligible to the general reader. The vertebræ of the Iguanodon are distinguishable from those of other reptiles which occur in the same strata by the following peculiarities, which the figure of a perfect specimen of a caudal vertebra (_Lign. 206, fig 3_) will serve to illustrate. The body, or centrum, is either flat or somewhat depressed on both articular faces; its sides are nearly flat, or somewhat convex, vertically (as in _fig 3_), and slightly concave lengthwise, or from front to back: in some examples, the body is more contracted towards the inferior surface, as in _fig. 6_; and in the vertebræ, near the middle of the tail, the sides are compressed, so as to give an angular contour and somewhat vertical elongation to the face, as in _fig. 4_; but in the dorsal vertebræ, the articular faces are nearly circular, but somewhat higher than wide. In the caudal vertebræ, the inferior angles of the body are truncated (_w, figs. 3, 4_), and present an oblique, smooth face, to articulate with the chevron bone (_fig. 3, f_). The annular part is united to the body by suture (_fig. 3, o_), and anchylosed in the dorsal vertebræ; and in these bones the neural arch is very high, and greatly expanded, and its bases extend transversely inwards, and join each other below the spinal canal, forming a ring, or bony channel, to contain the spinal chord.[645] "The transverse processes are straight, and very long in the vertebræ from the middle of the trunk, indicating a considerable expanse of the abdominal cavity, adapted for the lodgment of the capacious viscera of a herbivorous quadruped." (_Owen._) The spinous processes (_Lign. 206, fig. 3, d_) are large and of great height in the anterior caudal vertebræ, _Lign. 224_; and here the chevrons, or hæmapophyses (_Lign. 224, b_, and _Lign. 206_, _fig. 2_, and _fig. 3, f_), are also of considerable length; the bases of the latter are always united (_Lign. 206, fig. 2, g_), and often blended, so as to form but one face for articulation with the truncated inferior angles of the body of the vertebra:, leaving a vertically elongated channel for the passage of the large blood-vessels of the tail. The external surface of the vertebræ of the Iguanodon is more or less marked with fine longitudinal striæ; those of the Megalosaurus have a smoother and more polished surface.[646]

[644] A detailed account of the elements of the spinal column of the Iguanodon, and remarks on various fossil vertebræ, the relations of which with the Iguanodon have been considered doubtful, will be found in _Petrif._ pp. 256-279.

[645] See also lithographs of dorsal and caudal vertebræ from the Kentish Rag; Owen’s _Monog. Cret. Rept._ (Pal. Soc.) 1851.

[646] See Rep. Brit Assoc. 1841, pp. 125-133, where an elaborate investigation of the vertebra: of the Iguanodon is given by Professor Owen.

Bones of the Extremities. _Ligns._ 225 and 226.--The thigh-bone (_femur_), both bones of the leg (_tibia_ and _fibula_), and many of the metatarsal and phalangeal bones have been discovered; the osteology of the hinder extremity is, therefore, almost perfect. The thigh-bone (_Lign. 225_; and _Petrif._ p. 292,) is of a very remarkable character, having a closer resemblance to the femur of a huge mammalian, than to that of a reptile.[647] Several perfect specimens have been discovered, as well as the associated bones of the leg (_Petrif._ p. 293, _Lign._ 62); but the first fragment that came under my notice, was the middle portion of the shaft of a femur of enormous size, and of an irregular quadrangular form; and so shapeless and unintelligible it then appeared, that several years elapsed before its real nature was determined. (_Foss. Tilg. For._ pl. xviii.)

[647] See Cuvier’s _Ossem. Foss._ vol. ii. p. 36.

An entire thigh-bone of an adult Iguanodon, from the Weald clay in the west of Sussex, measured three feet eight inches in length.[648] end thirty-five inches in circumference at the condyles; and I have a femur of a very young animal, that is but five inches long. The form of the thigh-bone is so peculiar, that fragments may easily be recognised. The head of the femur (_Lign. 225, f_,) is hemispherical, and projects inwards; there is no appearance of a _ligamentum teres_; a flattened process or trochanter (_Lign. 225, a_,) forms the external boundary of the neck of the bone, from which it is separated by a deep and narrow vertical fissure; the shaft is of a sub-quadrangular shape, and a slightly elevated ridge, produced by the union of two broad, flat, longitudinal surfaces, extends down the middle of the anterior face, and, diverging towards the inner condyle, gradually disappears. The bone terminates below in two large condyles, separated in front and behind by a deep, narrow cleft, or groove (_Lign. 225, e_). Near the middle of the inner edge of the shaft, there is a compressed ridge, with an angular projection, or trochanter. Thus the upper part of the femur maybe known by the presence of the flattened, or laterally compressed trochanter; and if that process be wanting, a fractured surface indicating its position may be detected; the middle of the shaft is characterized by its broad angular faces, and the inner submedian trochanter: the condyloid or inferior extremity of the bone may be distinguished by the deep groove between the condyles, both in front and behind.

[648] The average length of the adult femur is estimated at about four feet five inches.

The arm-bone (_humerus_) of the Iguanodon has been discovered in the Wealden of the Isle of Wight by Mr. Fowlstone; it is figured and described in _Petrif._ p. 286. The humerus is also present in the Maidstone specimen[649] of Iguanodon, before referred to at page 692: in pl. ii. of _Wond._ this bone is termed the _radius_. The humerus of this reptile is much smaller than the femur; in the Maidstone specimen the former is about 20 inches, and the latter about 33 inches in length.

[649] The two bones marked "6" in pl. ii. _Wond._ and in _Lign._ 65, _Petrif._ (one of which is figured in outline in _Lign. 226, fig. 4_,) regarded by Prof. Owen as the _radius_ and _ulna_ (the two bones of the fore-arm): the author’s reasons for regarding these bones as _metacarpals_ are given in full at p. 289, _Petrif._

As separate bones of the feet of the Iguanodon, for example, _metacarpals_, _metatarsals_, _phalangeals_, and _unguals_, often occur in the strata of the Wealden, figures of several specimens, on a reduced scale, are introduced in _Lign. 226_, and may enable the student to identify those he may meet with in his researches.[650] The ungual phalanges, or claw-bones, which were invested with the nail, are sometimes found of an enormous size; from a quarry near Horsham, Mr. Holmes obtained specimens more than five inches long, and three inches wide at the articular extremity.

[650] See Rep. Brit. Assoc. 1841, pp. 137-142.

Length of the Iguanodon.--The length of the united head and trunk, according to my estimate in _Geol. S. E._ p. 316, is seventeen feet and a half; by Professor Owen’s estimate it is reduced to fifteen feet;[651] a difference of no importance in such merely approximative calculations, particularly when the form of the cranium is unknown.[652]

[651] Ibid. p. 144.

[652] The more recently discovered specimen of lower-jaw, already referred to, page 693, indicates a length of between three and four feet for the entire jaw, _Petrif._ p. 249.

[653] This bone is conjecturally referred by Prof. Owen to the Megalosaurus.

The estimated extent of the tail has been subject to variation. My early estimate of its length gave rise to the idea of this reptile having attained seventy feet in length. Professor Owen, however, considered that the abbreviated character of the anterior caudal vertebræ indicated a far less extent of tail, which the Professor estimated at thirteen feet; this opinion, from the evidence then before us, seemed well founded, but from evidence since afforded by a series of eleven caudal vertebra, belonging to the middle region of the tail, that have been lately discovered, (_Petrif._ p. 312,) it is not at all improbable, that, instead of all the caudal vertebræ being abbreviated, these elements of the tail were elongated as in the corresponding part of the skeleton of the Iguana, and that the largest Iguanodons may have attained a length of from sixty to seventy feet.

The author’s physiological inferences as to the structure and economy of the Iguanodon, deduced from the study of the osseous remains of this singular creature, especially the lately discovered remains of the jaw-bones, are given in full at pp. 307-313 _Petrif._ or _Foss. Brit. Mus._: and at pp. 335-338, _ibid._ may be found some general remarks on the physical geography and the nature of the fauna and flora of the country inhabited by these stupendous reptiles, whose remains are so characteristic of the Wealden rocks.

Jaw of the Regnosaurus. (_Petrif._ p. 333.)--A portion of the right ramus, or side, of the lower jaw of this reptile was discovered in a block of sandstone from Tilgate Forest. It consists of a fragment, six inches long, of the dentary bones, with a small portion of the opercular; and it contains the fangs of fifteen teeth, which are closely and evenly set in a regular series, and imbedded laterally in grooves, or sockets, in the dentary bone; there are three or four sockets of successional teeth on the inner side of the bases of the old teeth. (_Phil. Trans._ 1841, pl. v. figs. 1, 2.) Unfortunately, all the crowns of the teeth are wanting. The outer parapet of the dentary piece is entire, and its upper margin is finely crenated. All the fangs of the teeth are exposed, but there are traces of a thin inner wall, indicating the probability that, as in the Megalosaurus, the teeth were supported medially by an osseous plate, and were implanted in distinct sockets.[654] In my memoir on this fossil jaw in the _Phil. Trans._ (1841, p. 131), I referred it to the genus Iguanodon; but subsequent observations have led me to conclude that it is generically distinct; and in my Memoir on the Jaw of the Iguanodon, in _Phil. Trans._ 1848 (p. 183), I have proposed for the animal to which it belonged the distinct generic appellation, Regnosaurus, with the specific name _Northamptoni_.

[654] The collector will perceive the importance that attaches to the discovery of even a fragment of the jaw of an unknown reptile, containing teeth in their natural position.

[Sidenote: LACERTIAN REPTILES.]

IV. Lacertian Reptiles.--The recent Lacertians, or true Lizards, are smaller and less highly organized reptiles than the Saurians of the Crocodilian order; and their dermal covering consists of a finer and more delicate squamous integument. They are also characterized by important modification in their osteological structure. The spinal column is almost always composed of concavo-convex vertebræ, with the convexity behind; the ribs are slender and rounded, having a single convex tubercle of attachment. The fossil species are, for the most part, of gigantic dimensions, and deviate in a striking manner from any that now exist. Vertebræ of the recent lacertian type are very rare in the secondary strata; I believe a few in my cabinet, obtained from the sandstone of Tilgate Forest, and which belonged to a very small unknown reptile, are the most ancient examples at present known.

Mosasaurus. _Bd._ pl. xx.; _Wond._ p. 311; _Petrif._ p. 193.--Of the fossil lizard of Maestricht, named _Mosasaurus_ (lizard of the Meuse) from the river adjacent to the quarries of St. Peter’s Mountain, in which its remains have been discovered, I have given a detailed account at pages 193-196 of _Petrif._ A specimen, with the jaws, and bones of the palate armed with teeth, now in the museum at Paris, has long been celebrated, and is still the most precious relic of this extinct reptile hitherto discovered; a reduced representation is given in _Lign. 227_; and _Pict. Atlas_, pl. lxx. This is the _Mosasaurus Hoffmanni_.[655] The specimen is four and a half feet long, and two and a half feet wide; it consists of both sides of the lower jaw, with the right ramus of the upper jaw in its natural position, and the left, which is displaced, lying across the articular extremity of the left branch of the lower jaw: of the pterygoid bones, which are armed with teeth; of the left tympanic bone (_os quadratum_), which is but little removed from its natural situation, and connects the lower jaw with the cranium; one of the metacarpal or metatarsal bones, and some fragments.[656]

[655] Several fine portions of the jaws, and many vertebræ of this animal, are in the British Museum: see _Foss. Brit. Mus._ p. 139. In a splendid work, _Histoire Naturelle de la Montagne de St. Pierre_, by the late Faujas St. Fond (1 vol. folio, with numerous plates), there are admirable figures of the remains of the Mosasaurus.

[656] In the British Museum there is a cast of this specimen, in a case near the bones of the Iguanodon.

Figs. 1_a_, 2_a_. Transverse sections of the crowns of the teeth, figs. 1 and 2 respectively.

[657] Reduced from figures accompanying Dr. Gibbes’s Memoir "On the Mosasaurus and three allied new genera," (with plates,) in the _Smithsonian Contributions_, vol. ii. 1849. This interesting paper comprises much information regarding the Mosasaurians of the Cretaceous deposits of N. America; but we cannot fully coincide with the author in his palæontological determinations.

The teeth are large, and supported on expanded conical osseous eminences, which are anchylosed to the alveolar ridge of the jaw (_acrodont_). The crown of the tooth is conical and recurved, with the outer face nearly flat, and this space is bordered on each side by a longitudinal ridge; giving the tooth somewhat of a pyramidal figure. (See _Ligns._ 228-230.) Professor Owen states that the crown consists of a body of simple and firm dentine, with fine and close-set calcigerous tubes, enclosing a simple pulp-cavity; irregular processes of the latter extend as medullary canals into the conical base of the tooth, but not, as in the Iguanodon, into the substance of the coronal dentine; the dentine is invested with a moderately thick coat of enamel.[658]

[658] See Odontography, p. 258, and pl. lxxii.; the student should also consult Cyclop. Anat. Phys. _Art._ Teeth.

The vertebræ of the Mosasaur, as is usual in the existing lizards and crocodiles, are concave in front and convex behind, and the neural arch is united to the centrum by suture. The entire vertebral column of _M. Hoffmanni_ appears to have consisted of 131 vertebræ, of which 97 belonged to the tail.[659] This Mosasaur was about twenty-five feet long.

[659] See Cuvier, _Oss. Foss._ vol. v. pp. 326-334.

This extinct lacertian reptile forms an intermediate link between the Saurians without pterygoid teeth (Monitors) and those with them (Iguanas). Its crocodilian affinities are but partial.

The Mosasaurus appears to have had webbed feet, adapted or crawling on land as well as for swimming,[660] and a long and vertically expanded tail, serving as a powerful oar, and enabling the animal to stem the roughest waters.

[660] See Prof. Owen’s observations on the bones that have been regarded as referable to the extremities of this creature, and especially on the phalangeal and other bones of the Mosasaur of the New Jersey greensand; _Monog. Cret. Rept._ 1851, pp. 36-40.

Prof. Goldfuss has described the remains of another and smaller species of Mosasaurus (_M. Maximiliani_), from Upper Missouri, U.S.; and Prof. Owen, in Dixon's "Fossils of Sussex," has established a third and still smaller species (_M. gracilis_),[661] to which he refers the four or five mosasaurian vertebræ found in the Chalk of Sussex. Two of these (caudal) are figured in _Geol. S. E._ p. 146, and _Petrif._ _Lign._ 44; and these and others are lithographed in plate viii. of Prof. Owen’s _Monog. Cret. Reptilia_, 1851.

[661] See also _Monograph on the Reptiles of the Chalk_, 1851, p. 31, and plate ix.

The remains of Mosasaurus occur also in the cretaceous sands of New Jersey, U. S. (See Dr. Morton’s _Synopsis of the Organic Remains of the United States_, 1834; and the Quart. Journ. of the Geological Society, vol. v. 1849.)

Leiodon anceps.[662]--Under this name Professor Owen has described a splendid fossil, consisting of a portion of the lower jaw of an acrodont reptile, with teeth, obtained by Edward Charlesworth, Esq. from the Chalk north of the Thames. This specimen was submitted to my inspection, many years since, by Mr. Charlesworth, and I then pointed out the analogy of this acrodont jaw to that of the Mosasaurus.

[662] Ibid. p. 42, pl. ix. A.

Prof. Owen in 1840 (_Odontog._ p. 261), and in 1841 (_Rep. Brit. Assoc._ p. 144), described and figured some teeth from the same specimen, which were lent by Mr. Charlesworth. These teeth the Hunterian Professor regarded as characteristic of a new genus of Mosasauroid reptile, to which he gave the name _Leiodon_ (in allusion to the smoothness of the teeth). In 1845 (_Rep. Brit. Assoc._ p. 60) Mr. Charlesworth noticed, and in 1846 (_London Geol. Journal_, p. 23, plates iv. and vi.) figured and described, the above mentioned portion of jaw with teeth, under the name _Mosasaurus stenodon_; and in 1851 Prof. Owen figured and described this specimen under the name of _Leiodon anceps_, which was originally proposed for the animal, as known from its teeth, in 1840.

The portion of bone on which the teeth, five in number are implanted is seven inches in length, and is, in Professor Owen s opinion, the dentary piece of the lower jaw, and not a portion of a pterygoid bone. Mr. Charlesworth has had a section made of four of the teeth, and finds that the pulp-cavities are more or less occupied with solid cones of silex, which must have permeated the osseous parietes of the teeth.

The teeth of Leiodon have a simple pulp-cavity, surrounded by fine dentine, with an external layer of smooth enamel. The apex of the crown is sharp-pointed; the body of the crown is slightly recurved; its base is expanded into a thick circular fang, which is anchylosed to a short conical process of the alveolar border of the jaw: the teeth differ from those of the Mosasaurus in having the outer side as convex as the inner side, the transverse section being an ellipse with pointed ends, which latter correspond with the lateral trenchant edges of the crown of the tooth: the teeth are more closely set than in the Mosasaur and Geosaur. (_Owen._)

Geosaurus Sœmmeringii. _Petrif._ p. 175.--In the British Museum are the remains of a reptile from the "white Jura" (upper oolite) of Monheim, in Franconia, which Cuvier describes as being more nearly related to the Lizards than Crocodiles. The length of this reptile is estimated at about ten feet. The eyes had a circle of osseous plates in the _sclerotica_, like those of the Ichthyosaurus; the teeth resemble those of the Mosasaurus in being sub-compressed and recurved, but they are at once distinguished by their anterior and posterior finely serrated sharp edges; the crown is invested with an external coat of enamel.[663]

[663] Oss. Foss. tom. v. p. 343.

Raphiosaurus subulidens.--A portion of a lower jaw, containing twenty-two closely set, subulate teeth, anchylosed by their bases to a shallow alveolar groove and an outer alveolar parapet of bone, as in the Iguana, thus corresponding with the pleurodont Lizards, is described under this name by Professor Owen, (_Geol. Trans._ 2d ser. vol. vi. pl. xxxix.); and _Monog. Cret. Rept._ (Pal. Soc.) 1851, p. 19, pl. x. figs. 5, 6. It is from the Lower Chalk, near Cambridge, and is in the collection of James Carter, Esq. of that place. Remains of Raphiosaurus have been found also in the Chalk at Northfleet, Kent.

Dolichosaurus longicollis.--In the Chalk of Kent was found, some years since, a considerable portion of the skeleton of a lacertian reptile, consisting of the posterior half of the spinal column, with remains of the pelvic and thigh bones; it was figured in the _Geol. Trans._ 2d ser. vol. vi. pl. xxxix.; and is now in the collection of Sir P. G. Egerton. From the researches of the late Mr. Dixon, it appears that a mutilated reptilian head and anterior portion of a spinal column, with fore-arm and scapular bones, now in the collection of Mr. Smith, of Tunbridge Wells, belong to the same skeleton as the vertebral remains above mentioned. Both specimens were obtained at the same time from the well-known chalk-pit at Burham, Kent. Professor Owen has lately described these interesting remains in detail (_Monog. Cret. Rept._ 1851, pp. 22, &c.), and finds no intrinsic contradiction to exist to the historical evidence adduced as to the probability of the two moieties having belonged to the same individual. In the two specimens there exist sixty-three concavo-convex (_procœlian_) vertebræ, of which fifty-seven form the series between the skull and the pelvis, giving the trunk a length of about eighteen inches. This unique reptile was elongate and snake-like in its form, with the abdomen deep and narrow, like that of the water-snakes: its limbs were short; its tail, from the character of the few caudal vertebræ remaining, must have been relatively long and powerful. This long and slender lacertian was therefore probably to a considerable degree aquatic in its habits, swimming with an undulatory eel-like movement.

The Dolichosaurus (_long-lizard_) presents somewhat of the ophidian character in the number and size of its cervical vertebræ, in the size and shape of its ribs, and in the slender proportions of its trunk and head; but, with these partial exceptions, its affinities are truly lacertian. (Owen.)

Rhynchosaurus articeps. _Lign. 231._--In a quarry of Upper New Red Sandstone at Grinsell, near Shrewsbury, Dr. O. Ward discovered a skull (3-1/2 inches long), vertebræ, ribs, bones of the pectoral and pelvic arches, portions of two femora with medullary cavities, and fragments of other bones of a very remarkable lacertian reptile (_Lign. 231_). The lower jaw is preserved with the skull in its natural position. The cranium in its general aspect resembles that of a turtle, rather than of a lizard; for the intermaxillary bones are double, as in Chelonians, and symmetrical, and are not united by a median process; they are very long, and curve downwards, giving the fore part of the skull the profile of a parrot. See _Lign. 231_.

There are no teeth apparent in either jaw: the margin of the upper maxillary has feeble dentations, but in the lower jaw even these indications are wanting, and it is probable that this reptile had its jaws encased by a bony or horny sheath, as in birds and turtles.[664] (Owen.)

[664] Rep. Brit. Assoc. 1841, p. 150. See also Camb. Phil. Trans, vol. vii. p. 357, tab. 5, 6.

Thecodontosaurus and Palæosaurus. _Ly._ p. 306, figs. 348, 349.--Numerous bones and teeth of reptiles occur in the Magnesian Conglomerate, near Bristol, and have been described by Dr. Riley and Mr. Stutchbury in an interesting memoir to which reference should be made for details (_Geol. Trans._ 2d ser. vol. v. p. 349, pl. xxix. xxx.). The bones denote an approach to the lizards; the teeth are implanted in sockets; these reptiles, therefore, belonged to the group termed thecodont, and the name _Thecodontosaurus_, given to these extinct Saurians by Dr. Riley, has reference to this character. The teeth are pointed, compressed laterally, slightly convex on each side, with a trenchant, finely serrated edge in front and behind; the fang is sub-cylindrical. Other teeth from the same deposit, possessing the same general characters, but distinguished by peculiarities of form, have been referred to another genus, named _Palæosaurus_. The vertebræ found associated with the teeth and jaws are biconcave, and are remarkably characterized by the great depth of the spinal canal in the middle of the centrum or body of the vertebræ, so that the spinal chord must have presented a moniliform or bead-like appearance. These reptiles, in their _thecodont_ type of dentition, biconcave vertebræ, double-headed ribs, and proportionate size of the bones of the extremities, are nearly allied to the _Teleosaurus_, (see _ante_, p. 679); but they combine a lacertian form of tooth, and a lacertian structure of the pectoral, and probably of the pelvic arches, with these crocodilian characters; they have also distinctive modifications: such, for example, as the moniliform spinal chord.[665]

[665] Owen; Rep. Brit. Assoc. 1841, p. 155, &c.

Dicynodon. _Ligns. 232, 233, 234._--This singular fossil reptile was discovered, by Mr. Bain, in South Africa. It is distinguished, by some remarkable peculiarities of structure, from other animals of the Saurian order; of which it represents a new tribe, or sub-order. The cranium is narrow; the nostrils are divided, as in Lizards, and not confluent, as in Chelonia; the skull, in other respects, much resembles in general appearance that of a Turtle; the orbits are large; the jaws are edentulous, as in the Turtles, with the exception of a pair of long tusks,[666] implanted in sockets in the upper maxillary bone, like those of the Walrus; these tusks are of a finer texture than that of the Crocodile’s teeth, and almost as dense as in the Hyæna. These creatures present in the most striking manner that blending of the peculiarities of several existing orders, which is continually presented to the palæontologist; for with a type essentially lacertian are combined crocodilian and chelonian modifications. Although no vestiges of these reptiles have been discovered in England or in Europe, yet the occurrence of an allied form, the _Rhynchosaurus_ (_Lign. 231_), in our New Red Sandstone, and the probability that the South African reptiliferous deposits may, from their position, belong to the Triassic Epoch, induce me to give a somewhat extended notice of these extraordinary fossils: and I am led to do so on another account, namely, because the memoir,[667] of which the following is a brief abstract, is so excellent an example of the manner in which such investigations should be conducted, so as to arrive at any satisfactory conclusions as to the characters and relations of the lost types of beings, whose fragmentary and petrified relics are the only vestiges that remain.

[666] Hence the generic name, _Dicynodon_: from δις (twice), and κυνὁδονς (canine tooth).

[667] Prof. Owen’s Memoir on the Dicynodon, Geol. Trans. 2d ser. vol. vii. pp. 59, _et seq._; and plates iii. to vi.

The fossils under consideration were exhumed some years since by Mr. Andrew Geddes Bain, from the intensely hard argillo-calcareous nodules of the sandstone strata which range over an immense tract of country beyond the mountains north of Capetown,[668] The extensive series of these and other fossils from South Africa, collected by the indefatigable labour of Mr. Bain, have lately been deposited in the British Museum; but the specimens described and figured in Prof. Owen’s Memoir, above alluded to, are nearly all that have as yet been successfully worked out from the exceedingly hard matrix in which the bones are imbedded. These consist of crania and jaws, referable to four species.[669]

[668] For a notice of the geological structure of this region, see Mr. Bain’s paper in Geol. Trans. 2d ser. vol. vii. pp. 53, &c.; and the abstract of a later Memoir by Mr. Bain, in the Literary Gazette, Dec. 18, 1852 (No. 1874).

[669] Namely, Dicynodon lacerticeps (_lizard-head_), D. testudiceps (_turtle-bead_), and D. strigiceps (_owl-head_), the trivial names of which have reference to the general form of the head; and D. Bainii, the largest, but unfortunately as yet the least known species, which takes the name of the intelligent and energetic discoverer and collector of the whole.

The most striking character in these crania is the presence of a pair of long, sharp-pointed, gently curved tusks, implanted in the superior maxillary bones, and which descend, one on each side of the fore-part of the lower jaw, as seen in _Ligns._ 232 and 233, _t_, _t′_. This is a dental character which, with this exception, is peculiar to the mammalia (the Walrus, Musk-deer, and Machairodus), and is rare even in that class.

_Examination of the skull._--One of the crania showed the median undivided process of a single _intermaxillary_ bone, ascending and separating _two distinct anterior nasal apertures_; in another, the boundaries of a very much contracted cranial cavity were evident: these characters combined to prove that the skulls were referable to air-breathing oviparous and cold-blooded animals, or Reptiles; but neither to Crocodilians nor Chelonians, and for the following reasons:--

1stly. The originals were not mammalians; for no mammalian has the _intermaxillary bone single_ (as in _Lign. 233, a_), or the _external bony nasal aperture double_; and neither mammalian nor bird has the cavity for the brain so relatively small as in this fossil.

2dly. They were not Crocodiles; for in all crocodiles the intermaxillary bone is divided by a suture, and the anterior nasal aperture is single and on the median line, as in mammalia.

3dly. They were not Chelonians; for all turtles have the nasal opening single and placed in the middle of the fore-part of the skull, in the very situation which, in the Dicynodon, is occupied by the convex imperforate median plate of the broad intermaxillary bone.

4thly. They could not be Fishes, as those animals have no well-defined external respiratory nasal apertures.

5thly. They were neither Batrachians (frogs) nor Ophidians (serpents); for, although the reptiles of these two orders have a single intermaxillary and double nostrils, like the fossils, the latter are at once separated from them by the presence of a strong and complete zygomatic arch (_Ligns._ 232 and 233, _g_, _d_), continued from the tympanic bone to the large immovably articulated superior maxillary.

Lastly, the characters last named, and the presence of vertical tympanic pedicles (_Lign. 232, l_), suspended by their upper part to the junction of the zygomatic and mastoid bones, prove the affinity to the lacertians or true lizards.

These bidental crania have certain characters in common with that of the Rhynchosaur, which is also, as we have before seen, of the true lacertian group, but the Dicynodonts are more nearly allied to the Crocodiles and the Chelonians than the Rhynchosaurus appears to be.

Referring to the original Memoir for anatomical details, I must limit this notice to a few additional general remarks. Both the jaws are edentulous, with the exception of the pair of tusks, as in Chelonians; there are no traces of teeth, or of their sockets, in the lower jaw, which is short and very deep, and anchylosed at the symphysis, as in turtles; the alveolar border forms a smooth trenchant edge, which shuts within the corresponding part of the upper jaw: it is probable that both jaws were covered by horn, as in the chelonians. The tusks are implanted in wide and deep conical alveoli in the suborbital part of the maxillary bone, and project about two inches beyond the sockets (_Lign. 232_); they are long and pointed, and are directed downwards and forwards, with a slight backward curve, and slightly converge towards their extreme points (_Lign. 233_). These teeth consist of a simple body of unvascular dentine, with a very thin external coat of enamel. The tooth-ivory is more dense than in any known reptile, and approaches in its intimate texture that of the canines of the carnivorous mammals. The base of the tooth has a conical cavity (_Lign. 234_), indicating a persistent matrix or dental pulp, the rest of the tooth without the socket being solid. There are no traces whatever of the germs of successional teeth. It is therefore inferred, that, like the tusks and scalpriform incisors of mammalia, the canine or maxillary teeth of the Dicynodon were capable of constant growth and renovation; thus offering an approach to the typical dentition of mammalia, unknown in any other reptiles.

As the points of the teeth in the only known perfect specimen are unworn, it is inferred that these tusks were not employed either as instruments for obtaining food, as in the Dugong, or for locomotion, as in the Walrus, but were simply offensive and defensive weapons.[670]

[670] See Prof. Owen’s detailed account of these curious dental organs in the Memoir already referred to, and in the _Art._ Teeth, in the Cyclopædia of Anatomy and Physiology.

Fig. 1.--Longitudinal section of the fang of the tooth implanted in its socket: 1/3 _nat. size_. 1_a_.--Transverse section of the tooth.

A few sub-biconcave vertebræ and other undetermined bones were associated with these remains; and many similar crania, both with and without the tusks, and other cranial remains with jaws armed with numerous teeth, as well as indications of smaller reptiles, form part of Mr. Bain’s collections now in the National Museum, awaiting the skilful manipulation of the experienced workman to clear away their hard investing matrix, and the scientific examination of the palæontologist to elucidate their zoological characters.

Telerpeton Elginense (Mantell). _Ligns._ 235 and 236.--This is the oldest Reptile yet known.[671] Its remains consist of the impression[672] of a skeleton of a small, four-footed, vertebrate animal, on a block of the Old Red or Devonian Sandstone from Spynie, near Elgin, North Britain. It was obtained by Mr. Patrick Duff, in 1851; and a detailed description of this unique fossil, with an illustrative plate, will be found in the Quarterly Journal of the Geological Society, vol. viii. pp. 100, _et seq._; together with a notice by Captain Brickenden of the geology of the district where the specimen was found, and a paper on some fossil foot-prints,[673] discovered by this geologist in the same rock.

[671] The word Telerpeton simply denotes the remote antiquity of this Devonian reptile of Scotland, τἡλε (far off), ἑρπετον (reptile); the trivial name, _Elginense_, records the locality from whence it was obtained.

[672] A model of this most delicate and valuable impression has been deposited in the palæontological gallery of the British Museum.

[673] A general notice of the fossil foot-prints, or _Ichnolites_, that have been referred to Reptiles will be given at a subsequent page of this chapter.

By reference to _Lign. 235_, it will be seen that the cranium is almost wholly lost; a few conical teeth, mostly of a very small size, were observed in connexion with the vestige of the jaws. The spinal column is represented by the impressions of about thirty-six vertebræ, eleven or twelve of which belong to its caudal portion. The vertebræ present some faint evidence of their possessing a biconcave form; the length of one of the dorsal vertebræ is 1/9th of an inch. There are twenty-one pairs of long slender ribs. The pectoral arch and anterior extremities have nearly disappeared in the fracture of the stone. The pelvis and sacrum are very obscure; the latter is formed probably of two anchylosed vertebra;. The thigh-bones are somewhat curved; the tibia is gently bowed, and expanded at each extremity. There are no remains of the feet.

_a._ The remains of the cranium.

_b, b._ Imprints of portions of the anterior extremities.

_c, c._ Well-defined impressions of the thigh-bones and leg-bones, with an obscure sub-quadrangular pelvis.

1. One of the teeth: _nat. size_ and _mag._

The structure of this reptilian skeleton, as far as the specimen can serve to show, indicates a peculiar type of organization, in which, as in numerous other extinct forms, in this, as in other Classes, osteological characters are associated which in existing oviparous quadrupeds are restricted to distinct orders and genera.

The _lacertian_ affinities of the Telerpeton are well marked in the relative size and form of the bones of its extremities, the situation of its pelvis, and probably in the articulation and the length of its ribs; but the contracted, biconcave centrum, and the short neural spine of the vertebræ, as well as the horizontality of the articulating surfaces of the zygapophyses, and the general uniformity of character throughout the spinal column, are to be regarded as _batrachian_ modifications. Probably the original was a peculiar type, which, in the present state of our knowledge, it would be rash to ascribe to either order. The length of the original animal could not have exceeded six or seven inches. _Lign. 236_ represents in outline the probable form of this small, but most interesting reptile.

V. Pterosaurians, or Flying Reptiles.--Pterodactylus (_wing-fingered reptile_). _Lign. 237._ _Petrif._ p. 187; _Wond._ p. 577; _Bd._ pl. xxi. xxii.--The extinct reptiles denominated Pterodactyles, constituting a few genera of an order of Saurians organized for aërial life,[674] are unquestionably the most marvellous even of the wonderful beings which the relics of the Age of Reptiles have enabled the palæontologist to reconstruct. With a long-snouted head and long neck, much resembling that of a bird, bat-like wings, and a small trunk and tail, with lacertian affinities in its skull, teeth, and skeleton, and with a bird-like structure of sternum and scapular arch, these creatures present an anomaly of structure as unlike their fossil contemporaries, as is the duck-billed Ornithorhynchus, of Australia, to existing animals. The cranium, or brain-case, is small; the jaws are either long, and armed with numerous sharp-pointed teeth, or toothless, like those of a bird. The teeth of the Pterodactyle are all laniary; they are simple, of a conical form, recurved, with but little difference in their form and size, and implanted in distinct sockets, with wide intervals between each. In some species there are twenty-eight or thirty in the lower, and twenty-two in the upper jaw.

[674] The only known recent reptile at all analogous is the little _Draco volans_ of the East Indian Islands; but even this can scarcely be regarded as a flying animal, its lateral membranous expansions, which are rather parachutes than wings, and formed by elongated ribs, not by the fingers, presenting but a rudimentary condition of wings compared with those of the Bat and the Pterodactyle.

The orbit is very large; the sclerotica consists of an annular row of bony plates, but less in number than in the Ichthyosaurus; the external orifice of the nostrils is near the orbits; remains of the _os hyoides_ (bone of the tongue) have been observed.

The cervical vertebræ are large and strong, and capable of great flexibility forwards and backwards, probably to allow the head to fall back to the centre of gravity during flight. There are frequently traces of ossified condition of the tendons of the muscles of the neck. This is well seen in _P. macronyx_ and _P. crassirostris_ (_Lign. 237_), and is a peculiarity dependent on the additional support required by the long neck of the animal.

The dorsal vertebræ are from seventeen to twenty in number. The sacrum is formed by the coalescence of two vertebræ only, as in existing reptiles, and not of many, as in birds and certain extinct saurians. The tail is generally short, an unusual character with saurians; but a species with a long tail occurs at Solenhofen.

There are five toes or digits on each foot; the outer finger of the fore-arm is immensely elongated, for the support of a membranous expansion (the impression of this wing-membrane is preserved on the stone in some examples); and the other digits, of fore and hind feet, terminated in long curved claws. The size and form of the extremities show that the _Pterodactylus_ was capable of perching on trees, of hanging against perpendicular surfaces, and of standing firmly on the ground, when, with its wings folded, it might crawl on all-fours, and walk or hop like a bird. A reference to the graphic description of the characters and probable habits of these beings, by Dr. Buckland, _Bd._ i. p. 221, and the beautiful illustrations accompanying it (_Bd._ ii. pl. xxi. xxii.), will equally instruct and gratify the reader.

The most perfect examples of the _Pterodactyles_ have been discovered in the lithographic stone of Monheim, Pappenheim, and Solenhofen, where their bones are associated with the remains of _Dragon-flies_ (see p. 551) and other insects. In England, bones of these reptiles have been obtained from the Lias of Lyme Regis, from the Oolitic slate of Stonesfield, from the Wealden strata of Tilgate Forest, and the Chalk of Kent.[675] One of the most interesting British specimens consists of a considerable part of the skeleton of a species about the size of a Raven, discovered by the late Mary Anning, in the Lias of Lyme Regis, and now deposited in the British Museum.[676] It consists of the principal bones of the extremities, and of several vertebra:, and is figured and described by Dr. Buckland, _Geol. Trans._ 2d ser. vol. iii. pl. xxvii. This specimen is distinguished by a greater length of the claws (whence the name of the species, _P. macronyx_, _long-claw_,) than in any previously known.

[675] For a detailed description of the Pterosaurian remains from the English Chalk, with numerous beautiful illustrations, see Prof. Owen s _Monograph_, published by the Palæontographical Society, 1851. Other important memoirs on Pterodactyles and their structure, not mentioned in the text, are, by Von Meyer, in _Nova Acta Acad. Nat. Curios._ vol. xv. part ii. and _Palæontographica_, part i. 1846; Goldfuss, _Nova Acta_, vol. xv. part i., and _Reptilien der Vorwelt_, 1831; Prof. Owen _Quart. Journ. Geol. Soc._ vol. iii. and Mr. Bowerbank, _ibid._ vol. iv.

[676] See _Petrif._ p. 189.

The remains of the Pterodactyles of the Chalk, for the most part, indicate a large size for the original animals. It has been estimated that some of these gigantic flying reptiles possessed an extent of wing surpassing that of the great albatross. The _Pterodactylus Cuvieri_ had probably an expanse of wing not less than eighteen feet from tip to tip; another Chalk species, _P. compressirostris_, fifteen feet; whilst the _P. macronyx_, of the Lias, measured about four feet seven inches from the extremity of one wing to that of the other.[677]

[677] Bowerbank, _Rep. Brit. Assoc._ 1851, and Owen, _Monograph_, p. 104.

[Sidenote: CHELONIANS.]

VI. Chelonian Reptiles.--Those singular reptiles, commonly known by the name of Tortoises and Turtles, and designated by naturalists Chelonia (from _Chelone_, the Greek term for a Tortoise), are distinguished from all other animals by the osseous cuirass in which their bodies are enclosed, the head and neck, extremities, and tail, alone being excluded. This remarkable bony case is produced by the extraordinary development of the bones of the thorax and back; and consists of an under (_sternal_) and an upper (_dorsal_) portion. The breast-plate, or _plastron_, which is the true sternum, is composed of nine pieces of bone, eight of which are in pairs, and the ninth, or odd plate, is situated between the four anterior plates. The variation in the form of these plates is considerable, and affords important distinctive characters. In the young state of land and fresh-water tortoises, there are vacancies between the pieces, which are filled up in the adult, the whole being ultimately united into one bony plate; but in the marine turtles (and also in the _Trionyces_, or soft tortoises), these pieces do not completely unite, and interspaces always remain. The bones of which the dorsal buckler, _carapace_, or upper shield is composed consist of eight of the ten pairs of ribs, united by a longitudinal series of angular plates, which are attached to the annular part of the vertebra throughout the whole, or a great part of their length, according to the age and species of the individual.[678] Numerous modifications exist in the form of the buckler, in its flatness or convexity, in the degree of extension of the ribs, and their angular plates, and in the characters of the scutes or horny integument with which the carapace is covered; and with corresponding variations in the head, and in the locomotive extremities, in the numerous species and genera of the Chelonian reptiles, according to their adaptation to a terrestrial, fluviatile, or marine existence.

[678] In the Monograph on Eocene Reptiles, 1849, Prof. Owen has given a succinct account of the carapace and plastron of the _Chelone_, and a brief notice of the composition and homologies of these bony encasements in the Tortoise, with references to more particular and comprehensive memoirs by himself and others.

The animals of this order are arranged in four principal groups, viz. the marine, or Turtles (_Chelones_); the fluviatile, or river-Tortoises (_Trionyces_); the marsh-Tortoises (_Emydes_); and the terrestrial or land-Tortoises (_Testudines_). The marine Chelonians generally feed upon vegetables; the _Emys_ and _Trionyx_ approach more nearly to the terrestrial than to the marine species; they are carnivorous, feeding on frogs, fishes, fresh-water mollusca, and other small animals. The _Trionyces_ differ from their congeners in being destitute of a horny external integument, having no scutes on the buckler or any other part of the body but the osseous carapace is invested with a strong tough skin, which equally covers the dorsum and sternum, to which it firmly adheres; the dermal surface of the bones in these Tortoises is always rugose, and either granulated, or covered with punctations and depressions. The buckler of the Trionyces is of a depressed form, with a soft flattened margin. The Testudinidæ, or land-Tortoises, are too well known to render any description requisite for our present purpose.

In the marine species, eight pairs of ribs and thirteen plates of the longitudinal series form the buckler; the ribs or costal plates are united to each other through a great part of their extent; but towards their distal or outer extremities each rib contracts, and terminates in a point, which is supported on a marginal series of bony plates; the intervals between the ribs are filled up in the living animal by a cartilaginous membrane which never becomes ossified. This character, therefore, affords an important aid in the discrimination of the fossil remains of this family.[679]

[679] The reader will recognise this peculiarity in the gilded skeleton of the carapace of Turtles, frequently exhibited in the soup-shops of the metropolis.

In the terrestrial and the marsh Tortoises, the ossification is complete in the adult state; but in the fluviatile Trionyces, which are without a horny integument, there is no border, or marginal series of bony plates, and the extremities of the ribs are therefore always distinct, and generally have an obtuse extremity. The skeletons of the three groups present corresponding modifications, and an accurate knowledge of the osteology of the recent animals is necessary to enable the palæontologist to arrive at secure conclusions as to the characters and relations of the fossil species.[680] We can only advert to one remarkable osteological character,--the construction of the shoulder, which differs from that of all other animals, in being situated within the cavity of the thorax, instead of without. In consequence of this modification, a process of the shoulder-blade (_scapula_ or _omoplate_), termed the _acromion_, is largely developed, and the shoulder-bone is tri-mucronate, or three-pronged, consisting of a short, thick head, containing a concavity (which, with that on the coracoid-bone, forms a socket for the arm-bone), and of two diverging branches. This form is so peculiar, that the collector can be at no loss to recognise the shoulder-bone of a _Chelonian_, should it come under his notice with other fossil relics (see _Foss. Til. For._ pl. xix. _fig._ 11). The shoulder-blade and its associated coracoid-bone undergo certain modifications in the three groups of Turtles, by which the anatomist may pretty certainly determine the terrestrial, fluviatile, or marine character of the animals to which they belonged. The successful application of a perfect knowledge of this department of osteology, is admirably exemplified in the works to which reference has been made; and even but a slight acquaintance with its principles will often enable us to obtain some general information as to the nature and relations of fossil Chelonians.

[680] The student should consult Cuvier’s _Ossemens Fossiles_, tom. v.