Part 2

Many other specimens of detached bones, including vertebræ or parts of the back-bone, especially that part resting on the hind limbs, and called the “pelvis,” bones of the limbs, down to those that supported the claws, together with jaws and teeth, which have since been successively discovered, have enabled anatomists to reconstruct the extinct Iguanodon, and have proved it to have been a herbivorous reptile, of colossal dimensions, analogous to the diminutive Iguana in the form of its teeth, but belonging to a distinct and higher order of reptiles, more akin to the crocodiles. The same rich materials, selecting the largest of the bones as a standard, have served for the present restorations (Nos. 4 and 5) of the animal, as when alive: all the parts being kept in just proportion to the standard bones, and the whole being thus brought to the following dimensions:—

Total length, from the nose or muzzle 34 feet 9 inches. to the end of the tail Greatest girth of the trunk 20 ” 5 ” Length of the head 3 ” 6 ” Length of the tail 15 ” 6 ”

The character of the scales is conjectural, and the horn more than doubtful, though attributed to the Iguanodon by Dr. Mantell and most geologists.

This animal probably lived near estuaries and rivers, and may have derived its food from the _Clathrariæ_, _Zamiæ_, _Cycades_, and other extinct trees, of which the fossil remains abound in the same formations as those yielding the bones and teeth of the Iguanodon.

These formations are the Wealden and the Neocomian or green-sand: the localities in which the remains of the Iguanodon have been principally found, are the Weald of Kent and Sussex: Horsham, in Sussex; Maidstone, in Kent; and the Isle of Wight.

Restorations of the _Cycas_ and _Zamia_ are placed, with the Iguanodon, on the Wealden division of the Secondary Island.

No. 6.—The Hylæosaurus. (_Hylæosaurus Owenii._)

The animal, so called by its discoverer, Dr. Mantell, belongs to the same highly organised order of the class of reptiles as the Iguanodon, that, viz., which was characterised by a longer and stronger sacrum and pelvis, and by larger limbs than the reptiles of the present day possess; they were accordingly better fitted for progression on dry land, and probably carried their body higher and more freely above the surface of the ground.

Visiting, in the summer of 1832, a quarry in Tilgate Forest, Dr. Mantell had his attention attracted to some fragments of a large mass of stone, which had recently been broken up, and which exhibited traces of numerous pieces of bone. The portions of the rock, which admitted of being restored together, were cemented, and then the rock was chiselled from the fossil bones, which consisted of part of the back-bone or vertebral column, some ribs, the shoulder bones called scapula and coracoid, and numerous long angular bones or spines which seemed to have supported a lofty serrated or jagged crest, extended along the middle of the back, as in some of the small existing lizards, _e.g._, the Iguana: cut No. 6. Many small dermal bones were also found, which indicate the Hylæosaurus to have been covered by hard tuberculate scales, like those of some of the Australian lizards, called _Cyclodus_.

This character of the skin, and the serrated crest, are accurately given in the restoration, the major part of which, however, is necessarily at present conjectural, and carried out according to the general analogies of the saurian form. The size is indicated with more certainty according to the proportions of the known vertebræ and other bones.

THE OOLITE.

The division of the secondary formations, called “Oolite,” takes its name from the most characteristic of its constituents, which is a variety of limestone composed of numerous small grains, resembling the “roe” or eggs of a fish, whence the term, (from the Greek _oon_, an egg, _lithos_, a stone). The oolite, however, includes a great series of beds of marine origin, which, with an average breadth of thirty miles, extend across England, from Yorkshire in the north-east to Dorsetshire in the south-west.

The oolite series lies below the Wealden, and where this is wanting, below the chalk, and consists of the following subdivisions, succeeding each other in the descending order:—

Oolite.

Upper. Portland stone and sand. Kimmeridge clay.

Middle. Coral rag. Oxford clay.

Lower. Cornbrash and forest marble. Great oolite and Stonesfield slate. Fuller’s earth. Inferior oolite.

Upon the portion of the island representing the oolite series, the most conspicuous of the restored animals of that period is—

No. 7.—The Megalosaurus.

The Megalosaurus, as its name implies (compounded by its discoverer, Dr. Buckland, from the Greek _megas_, great, and _sauros_, lizard), was a lizard-like reptile of great size, “of which,” writes Dr. Buckland, “although no skeleton has yet been found entire, so many perfect bones and teeth have been discovered in the same quarries, that we are nearly as well acquainted with the form and dimensions of the limbs as if they had been found together in a single block of stone.”

The restoration of the animal has been accordingly effected, agreeably with the proportions of the known parts of the skeleton, and in harmony with the general characters of the order of reptiles to which the Megalosaurus belonged. This order—the Dinosauria (Gr. _deinos_, terribly great _sauros_, a lizard)—is that to which the two foregoing huge reptiles of the Wealden series belong, viz., the Iguanodon and Hylæosaurus, and is characterised by the modifications already mentioned, that fitted them for more efficient progression upon dry land. The Iguanodon represented the herbivorous section of the order, the Hylæosaurus appears, from its teeth, to have been a mixed feeder, but the Megalosaurus was decidedly carnivorous, and, probably, waged a deadly war against its less destructively endowed congeners and contemporaries.

Baron Cuvier estimated the Megalosaurus to have been about fifty feet in length; my own calculations, founded on more complete evidence than had been at the Baron’s command, reduce its size to about thirty-five feet:[3] but with the superior proportional height and capacity of trunk, as contrasted with the largest existing crocodiles, even that length gives a most formidable character to this extinct predatory reptile.

As the thigh-bone (_femur_) and leg-bone (_tibia_) measure each nearly three feet, the entire hind-leg, allowing for the cartilages of the joints, must have attained a length of two yards: a bone of the foot (metatarsal) thirteen inches long, indicates that part, with the toes and claws entire, to have been at least three feet in length. The form of the teeth shows the Megalosaurus to have been strictly carnivorous, and viewed as instruments for providing food for so enormous a reptile, the teeth were fearfully fitted to the destructive office for which they were designed. They have compressed conical sharp-pointed crowns, with cutting and finely serrated anterior and posterior edges; they appear straight, as seen when they had just protruded from the socket, but become bent slightly backwards in the progress of growth, and the fore part of the crown, below the summit, becomes thick and convex.

A minute and interesting description of these teeth will be found in Dr. Buckland’s admirable “Bridgewater Treatise” (vol. i. p. 238), from which he concludes that the teeth of the Megalosaurus present “a combination of contrivances analogous to those which human ingenuity has adopted in the construction of the knife, the sabre, and the saw.” The fossils which brought to light the former existence of this most formidable reptile, were discovered in 1823, in the oolitic slate of Stonesfield, near Oxford, and were described by Dr. Buckland, in the volume of the “Geological Transactions” for the year 1824.

Remains of the Megalosaurus have since been discovered in the “Bath oolite,” which is immediately below the Stonesfield slate, and in the “Cornbrash,” which lies above it. Vertebræ, teeth, and some bones of the extremities have been discovered in the Wealden of Tilgate Forest, Kent, and in the ferruginous sand, of the same age, near Cuckfield, in Sussex. Remains of the Megalosaurus also occur in the Purbeck limestone at Swanage Bay, and in the oolite in the neighbourhood of Malton, in Yorkshire.

Mr. Waterhouse Hawkins’s restoration, according to the proportions calculated from the largest portions of fossil bones of the Megalosaurus hitherto obtained, yields a total length of the animal, from the muzzle to the end of the tail, of thirty-seven feet; the length of the head being five feet, the length of the tail fifteen feet; and the greatest girth of the body twenty-two feet six inches.

Nos. 8 & 9.—Pterodactyles of the Oolite.

To the right of the Hylæosaurus, on the rock representing the greater oolite formation, are restorations of species of Pterodactyle (_Pterodactylus Bucklandi_, No. 9), smaller than and distinct from those of the chalk formations. The remains of Buckland’s Pterodactyle are found pretty abundantly in the oolitic slate of Stonesfield, near Oxford.

Nos. 10 & 11.—Teleosaurus.

On the shore beneath the overhanging cliff of oolitic rock are two restorations, Nos. 10 and 11, of a large extinct kind of crocodile, to which the long and slender-jawed crocodile of the Ganges, called “Gaviàl” or “Gharriàl” by the Hindoos, offers the nearest resemblance at the present day. Remains of the ancient extinct British gavials have been found in most of the localities where the oolitic formations occur, and very abundantly in the lias cliffs near Whitby, in Yorkshire. The name Teleosaurus (_telos_, the end, _sauros_, a lizard), was compounded from the Greek by Professor Geoffroy St. Hilaire, for a species of these fossil gavials, found by him in the oolite stone at Caen, in Normandy, and has reference to his belief that they formed one—the earliest—extreme of the crocodilian series, as this series has been successively developed in the course of time on our planet.

The jaws are armed with numerous long, slender, sharp-pointed, slightly curved teeth, indicating that they preyed on fishes, and the young or weaker individuals of co-existing reptiles. The nostril is situated more at the end of the upper jaw than in the modern gavial: the fore-limbs are shorter, and the hind ones longer and stronger than in the gavial, which indicates that the Teleosaur was a better swimmer; the vertebræ or bones of the back are united by slightly concave surfaces, not interlocked by cup and ball joints as in the modern crocodiles, whence it would seem that the Teleosaur lived more habitually in the water, and less seldom moved on dry land; and, as its fossil remains have been hitherto found only in the sedimentary deposits from the sea, it may be inferred that it was more strictly marine than the crocodile of the Ganges.

The first specimen of a Teleosaur that was brought to light was from the “alum-schale” which forms one layer of the lofty lias cliffs of the Yorkshire coast, near Whitby. A brief description, and figures, of this incomplete fossil skeleton were published by Messrs. Wooller and Chapman, in separate communications, in the 50th volume of the “Philosophical Transactions,” in 1758. Captain Chapman observes, “it seems to have been an alligator;” and Mr. Wooller thought “it resembled in every respect the Gangetic gavial.” Thus, nearly a century ago, the true nature of the fossil was almost rightly understood, and various were the theories then broached to account for the occurrence of a supposed Gangetic reptile in a petrified state in the cliffs of Yorkshire. It has required the subsequent progress of comparative anatomy to determine, as by the characters above defined, the essential distinction of the Teleosaur from all known existing forms of crocodilian reptiles.

Very abundant remains, and several species, of the extinct genus have been subsequently discovered: but always in the oolitic and liassic formations of the secondary series of rocks.

The oolitic group of rocks are very rich in remains of both plants and animals: many reptiles of genera and species distinct from those here restored have been recognised and determined by portions of the skeleton. Extremely numerous are the remains of fishes, chiefly of an almost extinct order (_Ganoidei_), characterised by hard, shining, enamelled scales. But the most remarkable fossils are those which indisputably prove the existence, during the period of the “Great” or “Lower Oolite,” of insectivorous and marsupial mammalia—_i.e._, of warm-blood quadrupeds, which, like the shrew or hedgehog, fed on insects, and, like the opossum, had a pouch for the transport of the young. The lower jaw of one of these earliest known examples of the mammalian class, found in the Stonesfield slate, near Oxford, may be seen at the British Museum, to which it was presented by J. W. Broderip, Esq., F.R.S., by whom it was described in the “Zoological Journal,” vol. iii., p. 408.

It is interesting to observe that the marsupial genera, to which the above fossil quadruped, called _Phascolotherium_, was most nearly allied, are now confined to New South Wales and Van Diemen’s Land; since it is in the Australian seas that is found the _Cestracion_, a cartilaginous fish which has teeth that are most like those fossil teeth called _Acrodus_ and _Psammodus_, so common in the oolite. In the same Australian seas, also, near the shore, the beautiful shell-fish called _Trigonia_ is found living, of which genus many fossil species occur in the Stonesfield slate. Moreover, the Araucarian pines are now abundant, together with ferns, in Australia, as they were in Europe in the oolitic period.

THE LIAS.

“Lias” is an English provincial name adopted in geology, and applied to a formation of limestone, marl, and petrified clay, which forms the base of the oolite, or immediately underlies that division of secondary rocks. The lias has been traced throughout a great part of Europe, forming beds of a thickness varying from 500 to 1000 feet of the above-mentioned substances, which have been gradually deposited from a sea of corresponding extent and direction. The lias abounds with marine shells of extinct species, and with remains of fishes that were clad with large and hard shining scales. Of the higher or air-breathing animals of that period, the most characteristic were the

Enaliosauria.

The creatures called Enaliosauria or Sea-lizards (from the Greek _enalios_, of the sea, and _sauros_, lizard), were vertebrate animals, or had back bones, breathed the air like land quadrupeds, but were cold-blooded, or of a low temperature, like crocodiles and other reptiles. The proof that the Enaliosaurs respired atmospheric air immediately, and did not breathe water by means of gills like fishes, is afforded by the absence of the bony framework of the gill apparatus, and by the presence, position, and structure of the air passages leading from the nostrils, and also by the bony mechanism of the capacious chest or thoracic-abdominal cavity: all of which characters have been demonstrated by their fossil skeletons. With these characters the Sea-lizards combined the presence of two pairs of limbs shaped like fins, and adapted for swimming.

The Enaliosauria offer two principal modifications of their anatomical, and especially their bony, structure, of which the two kinds grouped together under the respective names of Ichthyosaurus and Plesiosaurus are the examples.

The Ichthyosaurus.

The genus Ichthyosaurus includes many species: of which three of the best known and most remarkable have been selected for restoration to illustrate this most singular of the extinct forms of animal life.

The name (from the Greek _ichthys_, a fish, and _sauros_, a lizard) indicates the closer affinity of the Ichthyosaur, as compared with the Plesiosaur, to the class of fishes. The Ichthyosaurs are remarkable for the shortness of the neck and the equality of the width of the back of the head with the front of the chest, impressing the observer of the fossil skeleton with a conviction that the ancient animal must have resembled the whale tribe and the fishes in the absence of any intervening constriction or “neck.”

This close approximation in the Ichthyosaurs to the form of the most strictly aquatic back-boned (vertebrate) animals of the existing creation is accompanied by an important modification of the surfaces forming the joints of the back-bone, each of which surfaces is hollow, leading to the inference that they were originally connected together by an elastic bag, or “capsule,” filled with fluid—a structure which prevails in the class of fishes, but not in any of the whale or porpoise tribe, nor in any, save a few of the very lowest and most fish-like, of the existing reptiles.

With the above modifications of the head, trunk, and limbs, in relation to swimming, there co-exist corresponding modifications of the tail. The bones of this part are much more numerous than in the Plesiosaurs, and the entire tail is consequently longer; but it does not show any of those modifications that characterise the bony support of the tail in fishes. The numerous “caudal vertebræ” of the Ichthyosaurus gradually decrease in size to the end of the tail, where they assume a compressed form, or are flattened from side to side, and thus the tail instead of being short and broad, as in fishes, is lengthened out as in crocodiles.

The very frequent occurrence of a fracture of the tail, about one fourth of the way from its extremity, in well-preserved and entire fossil skeletons, is owing to that proportion of the end of the tail having supported a tail-fin. The only evidence which the fossil skeleton of a whale would yield of the powerful horizontal tail-fin characteristic of the living animal, is the depressed or horizontally flattened form of the bones supporting such fin. It is inferred, therefore, from the corresponding bones of the Ichthyosaurus being flattened from side to side, that it possessed a tegumentary tail-fin expanded in the vertical direction. The shape of a fin composed of such perishable material is of course conjectural, but from analogies, not necessary here to further enlarge upon, it was probably like, or nearly like, that which the able artist engaged in the restoration of the entire form of the animal has given to it. Thus, in the construction of the principal swimming-organ of the Ichthyosaurus we may trace, as in other parts of its structure, a combination of mammalian (beast-like), saurian (lizard-like), and piscine (fish-like) peculiarities. In its great length and gradual diminution we perceive its saurian character; the tegumentary nature of the fin, unsustained by bony fin-rays, bespeaks its affinity to the same part in the mammalian whales and porpoises; whilst its vertical position makes it closely resemble the tail-fin of the fish.

The horizontality of the tail-fin of the whale tribe is essentially connected with their necessities as warm-blooded animals breathing atmospheric air; without this means of displacing a mass of water in the vertical direction, the head of the whale could not be brought with the required rapidity to the surface to respire; but the Ichthyosaurs, not being warm-blooded, or quick breathers, would not need to bring their head to the surface so frequently, or so rapidly, as the whale; and, moreover, a compensation for the want of horizontality of their tail-fin was provided by the addition of a pair of hind-paddles, which are not present in the whale tribe. The vertical fin was a more efficient organ in the rapid cleaving of the liquid element, when the Ichthyosaurs were in pursuit of their prey, or escaping from an enemy.

That the Ichthyosaurs occasionally sought the shores, crawled on the strand, and basked in the sunshine, may be inferred from the bony structure connected with their fore-fins, which does not exist in any porpoise, dolphin, grampus, or whale; and for want of which, chiefly, those warm-blooded, air-breathing, marine animals are so helpless when left high and dry on the sands: the structure in question in the Ichthyosaur is a strong osseous arch, inverted and spanning across beneath the chest from one shoulder-joint to the other; and what is most remarkable in the structure of this “scapular” arch, as it is called, is, that it closely resembles, in the number, shape, and disposition of its bones, the same part in the singular aquatic mammalian quadruped of Australia, called _Ornithorhynchus_, _Platypus_, and Duck-mole. The Ichthyosaurs, when so visiting the shore, either for sleep, or procreation, would lie, or crawl prostrate, or with the belly resting or dragging on the ground.

The most extraordinary feature of the head was the enormous magnitude of the eye; and from the quantity of light admitted by the expanded pupil it must have possessed great powers of vision, especially in the dusk. It is not uncommon to find in front of the orbit (cavity for the eye), in fossil skulls, a circular series of petrified thin bony plates, ranged round a central aperture, where the pupil of the eye was placed. The eyes of many fishes are defended by a bony covering consisting of two pieces; but a compound circle of overlapping plates is now found only in the eyes of turtles, tortoises, lizards, and birds. This curious apparatus of bony plates would aid in protecting the eyeball from the waves of the sea when the Ichthyosaurus rose to the surface, and from the pressure of the dense element when it dived to great depths; and they show, writes Dr. Buckland,[4] “that the enormous eye, of which they formed the front, was an optical instrument of varied and prodigious power, enabling the Ichthyosaurus to descry its prey at great or little distances, in the obscurity of night, and in the depths of the sea.”

Of no extinct reptile are the materials for a complete and exact restoration more abundant and satisfactory than of the Ichthyosaurus; they plainly show that its general external figure must have been that of a huge predatory abdominal fish, with a longer tail, and a smaller tail-fin: scale-less, moreover, and covered by a smooth, or finely wrinkled skin analogous to that of the whale tribe.

The mouth was wide, and the jaws long, and armed with numerous pointed teeth, indicative of a predatory and carnivorous nature in all the species; but these differed from one another in regard to the relative strength of the jaws, and the relative size and length of the teeth.

Masses of masticated bones and scales of extinct fishes, that lived in the same seas and at the same period as the Ichthyosaurus, have been found under the ribs of fossil specimens, in the situation where the stomach of the animal was placed; smaller, harder, and more digested masses, containing also fish-bones and scales have been found, bearing the impression of the structure of the internal surface of the intestine of the great predatory sea-lizard. These digested masses are called “coprolites.”

In tracing the evidences of creative power from the earlier to the later formations of the earth’s crust, remains of the Ichthyosaurus are first found in the lower lias, and occur, more or less abundantly, through all the superincumbent secondary strata up to, and inclusive of, the chalk formations. They are most numerous in the lias and oolite, and the largest and most characteristic species have been found in these formations.

No. 12.—Ichthyosaurus platyodon.