The Story of the Earth and Man

by Sir John William Dawson

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 than 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 than 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 than 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 than 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 than by the full-grown individuals.