Chapter VI: The Carboniferous Age (2)

Perhaps the most fish-like of the whole are the curious creatures from the coal measures of Saarbruck, first found by Yon Dechen, and which constitute the genus _Archegosaurus_. Their large heads, short necks, supports for permanent gills, feeble limbs, and long tails for swimming, show that they were aquatic creatures presenting many points of resemblance to the ganoid fishes with which they must have associated; still they were higher then these in possessing lungs and true feet, though perhaps better adapted for swimming then even for creeping.

From these creatures the other coal reptiles diverge, and ascend along two lines of progress, the one leading to gigantic crocodile-like animals provided with powerful jaws and teeth, and probably haunting the margins of the waters and preying on fishes; the other leading to small and delicate lizard-like species, with well-developed limbs, large ribs, and ornate horny scales and spines, living on land and feeding on insects and similar creatures.

In the first direction we have a considerable number of species found in the Jarrow coal-field in Ireland, and described by Professor Huxley. Some of them were like snakes in their general form, others more like lizards. Still higher stand such animals as _Baphetes_ and _Eosaurus_ from the Nova Scotia coal-field and _Anthracosaurus_ from that of Scotland. The style and habits of these creatures it is easy to understand, however much haggling the comparative anatomists may make over their bones. They were animals of various size, ranging from a foot to at least ten feet in length, the body generally lizard-like in form, with stout limbs and a flattened tail useful in swimming. Their heads were flat, stout, and massive, with large teeth, strengthened by the insertion and convolution of plates of enamel. The fore limbs were probably larger then the hind limbs, the better to enable them to raise themselves out of the water. The belly was strengthened by bony plates and closely imbricated scales, to resist, perhaps, the attacks of fishes from beneath, and to enable them without injury to drag their heavy bodies over trunks of trees and brushwood, whether in the water or on the land. Their general aspect and mode of life were therefore by no means unlike those of modern alligators; and in the vast swamps of the coal measures, full of ponds and sluggish streams swarming with fish, such creatures must have found a most suitable habitat, and probably existed in great numbers, basking on the muddy banks, surging through the waters, and filling the air with their bellowings. The most curious point about these creatures is, that while rigid anatomy regards them as allied in structure more to frogs and toads and newts then to true lizards, it is obvious to common sense that they were practically crocodiles; and even anatomy must admit that their great ribs and breastplates, and powerful teeth and limbs, indicate a respiration, circulation, and general vitality, quite as high as those of the proper reptiles. Hence, it happens that very different views are stated as to their affinities; questions into which we need not now enter, satisfied with the knowledge of the general appearance and mode of life of these harbingers of the reptilian life of the succeeding geological periods.

In the other direction, we find several animals of small size but better developed limbs, leading to a group of graceful little creatures, quite as perplexing with regard to affinities as those first mentioned, but tending towards the smaller lizards of the modern world. At the top of these I may place the genus _Hylonomus_ from hollow fossil trees of Nova Scotia, of which two species are represented as restored in our illustration. In these restorations I have adhered as faithfully as possible to the proportions of parts as seen in my specimens. Imagine a little animal six or seven inches long, with small short head, not so flat as those of most lizards, but with a raised fore-head, giving it an aspect of some intelligence. Its general form is that of a lizard, but with the hind feet somewhat large, to aid it in leaping and standing erect, and long and flexible toes. Its belly is covered with bony scales, its sides with bright and probably coloured scale armour of horny consistency, and its neck and back adorned with horny crests, tubercles, and pendants. It runs, leaps, and glides through the herbage of the coal forests, intent on the pursuit of snails and insects, its eye glancing and its bright scales shining in the sun. This is a picture of the best known species of Hylonomus drawn from the life. Yet the anatomist, when he examines the imperfectly-ossified joints of its backbone, and the double joint at the back of its skull, will tell you that it is after all little better then a mere newt, an ass in a lion's skin, a jackdaw with borrowed feathers, and that it has no right to have fine scales, or to be able to run on the land. It may be so; but I may plead in its behalf, that in the old coal times, when reptiles with properly-made skeletons had not been created, the next best animals may have been entitled to wear their clothes and to assume their functions as well. In short, functionally or officially, our ancient batrachians were reptiles; in point of rank, as measured by type of skeleton, they belonged to a lower grade. To this view of the case I think most naturalists will agree, and they will also admit that the progress of our views has been in this direction, since the first discovery of Carboniferous air-breathing vertebrates. In evidence of this I may quote from Professor Huxley's description of his recently found species,[O] After noticing the prevalent views that the coal reptiles were of low organization, he says: "Discoveries in the Nova Scotia coal-fields first shook this view, which ceased to be tenable when the great _Anthracosaurus_ of the Scotch coal-field was found to have well-ossified biconcave vertebrae."

[O] _Geological Magazine_, vol. iii.

The present writer may, however, be suspected of a tendency to extend forms of life backward in time, since it has fallen to his lot to be concerned in this process of stretching backward in several cases. He has named and described the oldest known animal. He has described the oldest true exogen, and the oldest known pine-tree. He was concerned in the discovery of the oldest known land snails, and found the oldest millipedes. He has just described the oldest bituminous bed composed of spore-cases, and he claims that his genus Hylonomus includes the oldest animals which have a fair claim to be considered reptiles. Still this discovery of old things comes rather of fortune and careful search then of a desire to innovate; and a distinction should be drawn between that kind of novelty which consists in the development of new truths, and that which consists in the invention of new fancies, or the revival of old ones. There is too much of this last at present; and it would be a more promising line of work for our younger naturalists, if they would patiently and honestly question nature, instead of trying to extort astounding revelations by throwing her on the rack of their own imaginations.

We may pause here a moment to contemplate the greatness of the fact we have been studying the introduction into our world of the earliest known vertebrate animals which could open their nostrils and literally "breathe the breath of life." All previous animals that we know, except a few Devonian insects, had respired in the water by means of gills or similar apparatus, Now we not only have the little land snails, with their imperfect substitutes for lungs, but animals which must have been able to draw in the vital air into capacious chambered lungs, and with this power must have enjoyed a far higher and more active style of vitality; and must have possessed the faculty of uttering truly vocal sounds. What wondrous possibilities unknown to these creatures, perhaps only dimly perceived by such rational intelligences as may have watched the growth of our young world, were implied in these gifts. It is one of the remarkable points in the history of creation in Genesis, that this step of the creative work is emphatically marked. Of all the creatures we have noticed up to this point, it is stated that God said, "Let the waters bring them forth"--but it is said that "God created" great reptiles (_tanninim_).[P] No doubt these "great tanninim" culminate in the succeeding Mesozoic age, but their first introduction dates as far back as the Carboniferous; and this introduction was emphatically a creation, as being the commencement of a new feature among living beings. What further differences may be implied in the formulæ, "Let the waters produce" and "God created," we do not know; very probably he who wrote the words did not fully know. But if we could give a scientific expression to this difference, and specify the cases to which its terms apply, we might be able to solve one of the most vexed questions of biology.

[P] Not "whales," as in our version.

Let us observe, however, that even here, where, if anywhere, we have actual creation, especial pains are taken to bridge over the gap, and to prevent any appearance of discontinuity in the work. The ganoid fishes of the coal period very probably had, like their modern congeners, well-developed air-bladders, serving to some extent, though very imperfectly, as lungs. The humbler and more aquatic reptiles of the period retained the gills, and also some of the other features of the fishes; so that, like some modern creatures of their class, they stood, as to respiration, on two stools, and seemed unwilling altogether to commit themselves to the new mode of life in the uncongenial element of air. Even the larger and more lizard-like of the coal reptiles may--though this we do not certainly know, and in some cases there are reasons for doubting it--have passed the earliest stage of their lives in the water as gilled tadpoles, in the manner of our modern frogs. Thus at the very point where one of the greatest advances of animal life has its origin, we have no sudden stop, but an inclined plane; and yet, as I have elsewhere endeavoured to show by arguments which cannot be repeated here,[Q] we have not a shadow of reason to conclude that, in the coal period, fishes were transmuted into reptiles.

[Q] "Air-breathers of the Coal Period," p. 77.

But the reader may be wearied with our long sojourn in the pestilential atmosphere of the coal swamps, and in the company of their low-browed and squalid inhabitants. Let us turn for a little to the sea, and notice the animal life of the great coral reefs and shell beds preserved for us in the Carboniferous limestone. Before doing so, one point merits attention. The coal formation for the first time distinctly presents to us the now familiar differences in the inhabitants of the open sea and those of creeks, estuaries and lakes. Such distinctions are unknown to us in the Silurian. There all is sea. They begin to appear in the Devonian, in the shallow fish-banks and the Anodon-like bivalves found with fossil plants. In the coal period they become very manifest. The animals found in the shales with the coal are all, even the aquatic ones, distinct from those of the open seas of the period. Some of them may have lived in salt or brackish water, but not in the open sea. They are creatures of still and shallow waters. It is true that in some coal-fields marine beds occur in the coal measures with their characteristic fossils, but these are quite distinct from the usual animal remains of the coal-fields, and mark occasional overflows of the sea, owing to subsidence of the land. It is important to notice this geographical difference, marking the greater specialisation and division of labour, if we may so speak, that was in the process of introduction.

The sea of the Carboniferous period presented in the main similar great groups of animals to those of the Devonian, represented however by different species. We may notice merely some of the salient points of resemblance or difference. The old types of corals continue in great force; but it is their last time, for they rapidly decay in the succeeding Permian and disappear. The Crinoids are as numerous and beautiful as in any other period, and here for the first time we meet with the new and higher type of the sea-urchin, in large and beautiful species. One curious group, that of the _Pentremites_, a sort of larval form, is known here alone. Among the lamp-shells we may note, as peculiarly and abundantly Carboniferous, those with one valve very convex and the other very concave and anchored in the mud by long spines instead of a peduncle attached to stones and rocks.[R] There are many beautiful shells allied to modern scallops, and not a few sea-snails of various sorts. The grand _Orthoceratites_ of the Silurian diminish in size preparatory to their disappearance in the Permian, and the more modern type of _Nautilus_ and its allies becomes prevalent. Among the Crustaceans we may notice the appearance of the _Limulus_, or king-crab, of which the single little species described by Woodward from the Upper Silurian may be regarded as merely a prophecy. It is curious that the Carboniferous king-crabs are very small, apparently another case of a new form appearing in humble guise; but as the young of modern king-crabs haunt creeks and swampy flats, while the adults live in the sea, it may be that only the young of the Carboniferous species are yet known to us, the specimens found being mostly in beds likely to be frequented by the young rather then by the full-grown individuals.

[R] The Productidæ.

The old order of the Trilobites, which has accompanied us from Primordial times, here fails us, and a few depauperated species alone remain, the sole survivors of their ancient race--small, unornamented, and feeble representatives of a once numerous and influential tribe. How strange that a group of creatures so numerous and apparently so well adapted to conditions of existence which still continue in the sea, should thus die out, while the little bivalved crustaceans, which began life almost as far back and lived on the same sea-floors with the Trilobites, should still abound in all our seas; and while the king-crabs, of precisely similar habits with the Trilobites, should apparently begin to prosper. Equally strange is the fate of the great swimming Eurypterids which we saw in the Devonian. They also continue, but in diminished force, in the Carboniferous, and there lay down for ever their well-jointed cuirasses and formidable weapons, while a few little shrimp-like creatures, their contemporaries, form the small point of the wedge of our great tribes of squillas and crabs and lobsters. Some years ago the late lamented palæontologist, Salter, a man who scarcely leaves his equal in his department, in conjunction with Mr. Henry Woodward, prepared a sort of genealogical chart of the Crustacea on which these facts are exhibited. Some new species have since been discovered, and a little additional light about affinities has been obtained; but taken as it stands, the history of the Crustacea as there shown in one glance, has in it more teaching on the philosophy of creation then I have been able to find in many ponderous quartos of tenfold its pretensions. Had Salter been enabled, with the aid of other specialists like Woodward, to complete similar charts of other classes of invertebrate animals, scientific palaeontology in England would have been further advanced then it is likely to be in the next ten years.

To return to our Trilobites: one of the most remarkable points in their history is their appearance in full force in the Primordial. In these rocks we have some of the largest in size--some species of Paradoxides being nearly two feet long, and some of the very smallest. We have some with the most numerous joints, others with the fewest; some with very large tails, others with very small; some with no ornamentation, others very ornate; some with large eyes, others with none that have been made out, though it is scarcely probable that they were wholly blind. They increased in numbers and variety through the Silurian and Devonian, and then suddenly drop off at the end of the Lower Carboniferous. Throughout their whole term of existence they kept rigidly to that type of the mud-plough which the king-crab still retains, and which renders the anterior extremity so different from that of the ordinary Crustacea. They constitute one of the few cases in which we seem to see before us the whole history of an animal type; and the more we look into that history, the more do we wonder at their inscrutable introduction, the unity and variety mingled in their progress, and their strange and apparently untimely end. I have already referred (page 95) to the use which Barrande makes of this as an argument against theories of evolution; but must refer to his work for the details.

One word more I must say before leaving their graves. I have reason to believe that they were not only the diggers of the burrows, and of the ladder-tracks and pitted tracks[S] of the Silurian and Primordial, but that with the strokes of their rounded or spinous tails, the digging of their snouts, and the hoe-work of their hard upper lips, or Hypostomes, they made nearly all those strange marks in the Primordial mud which have been referred to fucoids, and even to higher plants. The Trilobites worked over all the mud bottoms of the Primordial, even in places where no remains of them occur, and the peculiarities of the markings which they left are to be explained only by a consideration of the structures of individual species.

[S] _Climactichnites_ and _Protichnites_.

I had almost lost sight of the fishes of the Carboniferous period, but after saying so much of those of the Devonian, it would be unfair to leave their successors altogether unnoticed. In the Carboniferous we lose those broad-snouted plate-covered species that form so conspicuous a feature in the Devonian; and whatever its meaning, it is surely no accident that these mud-burrowing fishes should decay along with those crustacean mud-burrowers, the Trilobites. But swarms of fishes remain, confined, as in the Devonian, wholly to the two orders of the Gar-fishes (_Ganoids_) and the sharks (_Placoids_). In the former we have a multitude of small and beautiful species haunting the creeks and ponds of the coal swamps, and leaving vast quantities of their remains in the shaly and even coaly beds formed in such places. Such were the pretty, graceful fishes of the genera _Palæoniscus_ and _Amblypterus_. Pursuing and feeding on these were larger ganoids, armed with strong bony scales, and formidable conical or sharp-edged teeth. Of these were _Rhizodus_ and _Acrolepis_. There were besides multitudes of sharks whose remains consist almost wholly of their teeth and spines, their cartilaginous skeletons having perished. One group was allied to the few species of modern sharks whose mouths are paved with flat teeth for crushing shells. These were the most abundant sharks of the Carboniferous--slow and greedy monsters, haunting shell banks and coral reefs, and grinding remorselessly all the shell-fishes that came in their way. There were also sharks furnished with sharp and trenchant teeth, which must have been the foes of the smaller mailed fishes, pursuing them into creeks and muddy shallows; and if we may judge from the quantity of their remains in some of these places, sometimes perishing in their eager efforts. On the whole, the fishes of the Carboniferous were, in regard to their general type, a continuation of those of the Devonian, but the sharks and the scaly ganoids were relatively more numerous. They differed from our modern fishes in the absence of the ordinary horny-scaled type to which all our more common fishes belong, and in the prevalence of that style of tail which has been termed "heterocercal," in which the continuation of the backbone forms the upper lobe of the tail, a style which, if we may judge from modern examples, gives more power of upward and downward movement, and is especially suitable to fishes which search for food only at the bottom, or only above the surface of the waters.

Most reluctantly I must here leave one of the most remarkable periods of the world's history, and reserve to our next chapter the summation of the history of the older world of life in its concluding stage, the Permian.