Part 25

Enumeration of the Fossil Animals recognised by the Author.

In concluding this discourse, there only remains for me now to present the result of my own researches, or, in other words, a general account of my great work. I shall enumerate the animals which I have discovered, in the inverse order of that which I have followed in my enumeration of the formations. By proceeding deeper and deeper into the series of strata, I there rose in the series of epochs. I shall now take the oldest formations,--make known the animals which they contain,--and, passing from one epoch to another, point out those which successively make their appearance in proportion as we approach the present time.

We have seen that zoophytes, mollusca, and certain crustacea, begin to appear in the Transition formations; perhaps there may even at that period be bones and skeletons of fishes; but we do not by any means observe at so early a period remains of animals which live on land, and respire air in its ordinary state.

The great beds of coal, and the trunks of palms and ferns of which they preserve the impressions, although they afford evidence of the existence of dry land, and of a vegetation no longer confined to the waters, do not yet shew bones of quadrupeds, not even of oviparous quadrupeds.

It is only a little above this, in the bituminous copper-slates, that we see the first traces of them; and, what is very remarkable, the first quadrupeds are reptiles of the family of lizards, very much resembling the large monitors which live at the present day in the torrid zone. Several individuals of this kind have been found in the mines of Thuringia, among innumerable fishes of a genus now unknown, but which, from its relations to the genera of our days, appears to have lived in fresh water. Every body knows that the monitors are also fresh water animals.

A little higher is the limestone called Alpine, and resting upon it the shell-limestone, so rich in entrochites and encrinites, which forms the basis of a great part of Germany and Lorraine.

In it have been found skeletons of a very large sea-tortoise, the shells of which might have been from six to eight feet in length; and those of another oviparous quadruped of the family of lizards, of a large size, and with a very sharp muzzle.

Rising still through sandstones, which present only vegetable impressions of large arundinaceæ, bamboos, palms, and other monocotyledonous plants, we come to the different strata of the deposit which has been named the Jura limestone, on account of its forming the principal nucleus of that chain of mountains.

It is here that the class of Reptiles assumes its full development, and shews itself under the most varied forms and gigantic sizes.

The middle part, which is composed of oolites and lias, or of grey sandstone containing gryphites, contains the remains of two genera, the most extraordinary of all, which have combined the characters of the class of oviparous quadrupeds with organs of motion similar to those of the cetacea.

The ichthyosaurus, discovered by Sir Everard Home, has the head of a lizard, but prolonged into an attenuated muzzle, armed with conical and pointed teeth; enormous eyes, the sclerotica of which is strengthened by a frame consisting of bony pieces; a spine composed of flat vertebræ, of a depressed circular form, and concave on both surfaces like those of fishes; slender ribs; a sternum and clavicles like those of lizards and ornithorynchi; a small and weak pelvis; and four limbs, of which the humeri and femurs are short and thick, while the other bones are flattened, and closely set like the stones in a pavement, so as to form, when enveloped with the skin, fins of a single piece, almost incapable of bending; analogous, in short, both as to use and organization, to those of cetacea. These reptiles have lived in the sea; on shore, they could only at most have crept in the hobbling manner of seals; at the same time after they have respired elastic air.

The remains of four species have been found:

The most extensively distributed (I. communis) has blunt conical teeth; its length sometimes exceeds twenty feet.

The second (I. platyodon), which is at least as large as the former, has compressed teeth, with round and bulging roots.

The third (I. tenuirostris), has slender and pointed teeth, and the muzzle thin and elongated.

The fourth (I. intermedius), is, as its name implies, intermediate between the last species and the common, with respect to the form of its teeth. The two latter species do not attain half the size of the two first.

The plesiosaurus, discovered by Mr Conybeare, must have appeared still more monstrous than the ichthyosaurus. It had the same limbs, but somewhat more elongated and more flexible; its shoulder and pelvis were more robust; its vertebræ had more of the forms and articulations of the lizards; but what distinguished it from all oviparous and viviparous quadrupeds, was a slender neck as long as its body, composed of thirty and odd vertebræ, a number greater than that of the neck of any other animal, rising from the trunk like the body of a serpent, and terminating in a very small head, in which all the essential characters of that of the lizard family are observed.

If any thing could justify those hydras and other monsters, the figures of which are so often presented in the monuments of the middle ages, it would incontestibly be this plesiosaurus.

Five species are already known, of which the most generally distributed (P. dolichodeirus) attains a length of more than twenty feet.

A second species (P. recentior), found in more modern strata, has the vertebræ flatter.

A third (P. carinatus) shews a ridge on the under surface of its vertebræ.

A fourth, and lastly a fifth (P. pentagonus and P. trigonus), have the ribs marked with five and three ridges.

These two genera are found everywhere in the lias: they were discovered in England, where this rock is exposed in cliffs of great extent; but they have also been found since in France and Germany.

Along with these had lived two species of Crocodiles, the bones of which are also found deposited in the lias, among ammonites, terebratulæ, and other shells of that ancient sea. We have skeletons of them in our cliffs at Honfleur, where the remains are found, from which I have drawn up their characters.

One of these species, the Long-beaked Gavial, has the muzzle longer, and the head more narrow, than the gavial or long-beaked crocodile of the Ganges; the bodies of its vertebræ are convex before, while in our crocodiles of the present day they are so behind. It has been found in the lias deposits of Franconia, as well as in those of France.

A second species, the Short-beaked Gavial, has the muzzle of ordinary length, less attenuated than the gavial of the Ganges, but more so than our crocodiles of St Domingo. Its vertebræ are slightly concave at each of their extremities.

But these crocodiles are not the only ones which have been deposited in the strata of these secondary limestones.

The beautiful oolite quarries of Caen have presented a very remarkable one, the muzzle of which is as long and more pointed than that of the long-beaked gavial, and its head more dilated behind, with wider temporal fossæ. Its stony scales, marked with small round cavities, must have rendered it the best defended of all the crocodiles. Its lower teeth are alternately longer and shorter.