Chapter X: The Oldest Air-Breathers (1)

Animal life had its beginning in the waters, and to this day the waters are the chief habitat of animals, especially of the lower forms. If we divide the animal kingdom into great leading types, the lowest of these groups, the Protozoa, includes only aquatic forms; the next, that of the coral animals and their allies, is also aquatic. So are all the species of the Sea Urchins and Star Fishes. Of the remaining groups, the Mollusks, the Crustaceans, and the Worms are dominantly aquatic, only a small proportion being air-breathers. It is only in the two remaining groups, including the Insects and Spiders on the one hand, and the Vertebrate animals on the other, that we have terrestrial species in large proportion.

The same fact appears in geological time. The periods represented by the older Palæozoic rocks have been termed ages of invertebrates, and they might also be termed ages of aquatic animals. It is only gradually, and as it were with difficulty, that animals living in the less congenial element of air are introduced--at first a few scorpions and insects, later, land snails and amphibian reptiles, later still, the higher reptiles and the birds, and last of all the higher mammalia.

We need not wonder at this, for the conditions of life with reference to support, locomotion, and vicissitudes of temperature are more complex and difficult in air, and require more complicated and perfect machinery for their maintenance. Thus it was that probably half of the whole history of our earth had passed away before the land became the abode of any large number and variety of animals; while it was only about the same time that the development of the vegetable kingdom became so complete as to afford food and shelter for air-breathers.

It is also worthy of note that it is only in comparatively recent times that we have been able to discover the oldest air-breathing animals, and geologists long believed that the time when animals had existed on the land was even shorter than it had actually been. This arose in part from the infrequency and rarity of preservation of the remains of the earliest creatures of this kind, and perhaps partly from the fact that collectors were not looking for them.

That there was dry land, even in the Cambro-Silurian period, we know, and can even trace its former shores. In Canada our old Laurentian coast extends for more than a thousand miles, from Labrador to Lake Superior, marking the southern border of the nucleus of the American continent in the Cambrian and Cambro-Silurian periods. Along a great part of this ancient coast we have the sand flats of the Potsdam Sandstone, affording very favourable conditions for the imbedding of land animals, did these exist; still, notwithstanding the zealous explorations of the Geological Survey, and of many amateurs, no trace of an air-breather has been found. I have myself followed the oldest Palæozoic beds up to their ancient limits in some localities, and collected the shells which the waves had dashed on the beach, and have seen under the Cambro-Silurian beds the old pre-Cambrian rocks pitted and indented with weather marks, showing that this shore was then gradually subsiding; yet the record of the rocks was totally silent as to the animals that may have trod the shore, or the trees that may have waved over it. All that can be said is that the sun shone, the rain fell, and the wind blew as it does now, and that the sea abounded in living creatures. The eyes of Trilobites, the weathered Laurentian rocks, the wind ripples in the Potsdam sandstone, the rich fossils of the limestones, testify to these things. The existence of such conditions would lead us to hope that land animals may yet be found in these older formations. On the other hand, the gradual failure of one form of life after another, as we descend in the geological series, and the rarity of fishes and land plants in the Silurian rocks and their absence from the Cambrian, might induce us to believe that we have here reached the beginning of animal life, and have left far behind us those forms that inhabit the land.

Even in the Carboniferous period, though land plants abound, air-breathers are not numerous, and most of them have only been recently recognised. We know, however, with certainty that the dark and luxuriant forests of the coal period were not destitute of animal life. Reptiles[122] crept under their shade, land snails and millipedes fed on the rank leaves and decaying vegetable matter, and insects flitted through the air of the sunnier spots. Great interest attaches to these creatures; perhaps the first-born species in some of their respective types, and certainly belonging to one of the oldest land faunas, and presenting prototypes of future forms equally interesting to the geologist and the zoologist.

[122] I shall use the term reptile here in its broad, popular sense, as including Batrachians as well as reptiles proper.

It has happened to the writer of these pages to have had some share in the finding of several of these ancient animals. The coal formation of Nova Scotia, so full in its development, so rich in fossil remains, and so well exposed in coast cliffs, has afforded admirable opportunities for such discoveries, which have been so far improved that at least twenty-five out of the not very large number of known Carboniferous land animals have been obtained from it.[123] The descriptions of these creatures, found at various times and at various places, are scattered through papers ranging in date from 1844 to 1891,[124] and are too fragmentary to give complete information respecting the structures of the animals, and their conditions of existence.

[123] It appears that about a hundred species of Carboniferous reptiles have been recognised on the continent of Europe, in Great Britain, and in the United States. They belong to a number of distinct types, all, however, being of batrachian affinities.

[124] Papers by Lyell, Owen, and the author, in the _Journal of the Geological Society of London_, i. ii. ix. x. xi. xvi. xvii. xviii.; "Acadian Geology," by the author; Papers in _Trans. Royal Society of London_, _Am. Jl. of Science_, and _Geological Magazine_.

Footprints.

It has often happened to geologists, as to other explorers of new regions, that footprints on the sand have guided them to the inhabitants of unknown lands, and such footprints, proverbially perishable, may be so preserved by being filled up with matter deposited in them as to endure for ever. This we may see to-day in the tracks of sandpipers and marks of rain-drops preserved in the layers of alluvial mud deposited by the tides of the Bay of Fundy, and which, if baked or hardened by pressure, might become imperishable, like the inscriptions of the old Chaldeans on their tablets of baked clay. The first trace ever observed of reptiles in the Carboniferous system consisted of a series of small but well-marked footprints found by Sir W. E. Logan, in 1841, in the lower coal measures of Horton Bluff, in Nova Scotia; and as the authors of most of our general works on geology have hitherto, in so far as I am aware, failed to do justice to this discovery, I shall notice it here in detail. In the year above mentioned, Sir William, then Mr. Logan, examined the coal fields of Pennsylvania and Nova Scotia, with the view of studying their structure, and extending the application of the discoveries as to beds with roots, or Stigmaria underclays, which he had made in the Welsh coal fields. On his return to England he read a paper on these subjects before the Geological Society of London, in which he noticed the subject of reptilian footprints at Horton Bluff. The specimen was exhibited at the meeting of the Society, and was, I believe, admitted, on the high authority of Prof. Owen, to be probably reptilian. Unfortunately Sir William's paper appeared only in abstract in the Transactions; and in this abstract, though the footprints are mentioned, no opinion is expressed as to their nature. Sir William's own opinion is thus stated in a letter to me, dated June, 1843, when he was on his way to Canada, to commence the survey which has since developed so astonishing a mass of geological facts.

Natural size and reduced.

These footprints were the first indications of Carboniferous land vertebrates ever observed; they were probably made by a Microsaurian and one of the earliest species of this type. They show a remarkable length of stride and development of limb.]

"Among the specimens which I carried from Horton Bluff, one is of very high interest. It exhibits the footprints of some reptilian animal. Owen has no doubt of the marks being genuine footprints. The rocks of Horton Bluff are below the gypsum of that neighbourhood; so that the specimen in question (if Lyell's views are correct[125]) comes from the very bottom of the coal series, or at any rate very low down in it, and demonstrates the existence of reptiles at an earlier epoch than has hitherto been determined; none having been previously found below the magnesian limestone, or, to give it Murchison's new name, the 'Permian era.'"

[125] Sir Charles Lyell had then just read a paper announcing his discovery that the gypsiferous system of Nova Scotia is Lower Carboniferous, in which he mentions the footprints referred to, as being reptilian.

This extract is of interest, not merely as an item of evidence in relation to the matter now in hand, but as a mark in the progress of geological investigation. For the reasons above stated, the important discovery thus made in 1841, and published in 1842, was overlooked; and the discovery of reptilian bones by Von Dechen, at Saarbruck, in 1844, and that of footprints by Dr. King in the same year, in Pennsylvania, have been uniformly referred to as the first observations of this kind. Insects and Arachnidans, it may be observed, had previously been discovered in the coal formation in Europe.

The original specimen of these footprints is still in the collection of the Geological Survey of Canada, and a cast which Logan kindly presented to me is exhibited in the Peter Redpath Museum of McGill University. It is a slab of dark-coloured sandstone, glazed with fine clay on the surface; and having a series of seven footprints in two rows, distant about three inches; the distance of the impressions in each row being three or four inches, and the individual impressions about one inch in length. They seem to have been made by the points of the toes, which must have been armed with strong and apparently blunt claws, and appear as if either the surface had been somewhat firm, or the body of the animal had been partly water-borne. In one place only is there a distinct mark of the whole foot, as if the animal had exerted an unusual pressure in turning or stopping suddenly. One pair of feet--the fore feet, I presume--appear to have had four toes touching the ground; the other pair show only three or four, and it is to be observed that the outer toe, as in the larger footprints discovered by Dr. King, projects in the manner of a thumb, as in the cheirotherian tracks of the Trias. At a later date another series of footprints, possibly of the same animal, was obtained at the same place by Prof. Elder, and is now in the Peter Redpath Museum. Each foot in this shows five toes, and it is remarkable that the animal was digitigrade and took a long step for its size, indicating a somewhat high grade of quadrupedal organization. No mark of the tail or belly appears. The impressions are such as may have been made by animals similar to some of those to be described in the sequel.

Shortly afterward, Dr. Harding, of Windsor, when examining a cargo of sandstone which had been landed at that place from Parrsboro', found on one of the slabs a very distinct series of footprints, each with four toes, and a trace of the fifth. Dr. Harding's specimen is now in the museum of King's College, Windsor. Its impressions are more distinct, but not very different otherwise from those above described, as found at Horton Bluff. The rocks at that place are probably of nearly the same age with those of Parrsboro'. I afterward examined the place from which this slab had been quarried, and satisfied myself that the beds are Carboniferous, and probably Lower Carboniferous. They were ripple-marked and sun-cracked, and I thought I could detect some footprints, though more obscure than those in Dr. Harding's slab. Similar footprints are also stated to have been found by Dr. Gesner, at Parrsboro'. All of these were from the lowest beds of the Carboniferous system.

I have since observed several instances of such impressions at the Joggins, at Horton, and near Windsor, showing that they are by no means rare, and that reptilian animals existed in no inconsiderable numbers throughout the coal field of Nova Scotia, and from the beginning to the end of the Carboniferous period. Most of these, when well preserved, shew five toes both on the anterior and posterior limb. On comparing these earlier Carboniferous footprints with one another, it will be observed that they are of similar general character, and may have been made by one kind of animal, which must have had the fore and hind feet nearly of equal size, and a digitigrade mode of walking. Footprints of similar form are found in the coal formation, as well as others of much larger size. The latter are of two kinds. One of these shows short hind feet of digitigrade character and a long stride, in this resembling the smaller footprints of the Lower Carboniferous, which are remarkable for the length of limb which they indicate by the distance between the footprints. The other kind shows long hind feet, as if the whole heel were brought down to the ground in a plantigrade manner. These have also the outer toe separated from the others, and sometimes provided with a long claw. The fore foot is sometimes smaller than the hind foot, and differently formed.[126] In these respects they resemble the great Labyrinthodont Batrachians of the subsequent Trias. Their stride also is comparatively short, and the rows of impressions wide apart, as if the body of the animal had been broad, and its limbs short.

[126] Fine slabs of these footprints have been presented by Mr. Sandford Fleming to the Geological Survey of Canada.

We have thus two types of quadrupedal footprints, to the first of which I have given the name Hylopus, and have restricted the term Sauropus,[127] to the second. The first apparently belongs to the usually small reptiles of the group _Microsauria_, which had a well-marked lizard-like form, with well-developed limbs, and perhaps also to some of the smaller Labyrinthodonts, the second to the group of _Labyrinthodontia_, which were often of large size and with stout and short limbs and plantigrade hind feet. There are also some small and uncertain tracks, which may have been made by newt-like animals with short feet, and a singular trail of large size, and with a row of impressions at each side (Diplichnites),[128] which, if made by a vertebrate animal, would seem to indicate that serpentiform shape which we know belonged to some Carboniferous Batrachians.

[127] Given by King.

[128] Impressions and Footprints of Animals, _Am. Jour. Sci._, 1873.

The bones of these animals, however, hitherto found in Nova Scotia, may all have belonged to the two groups first named, the Labyrinthodontia and Microsauria, and I shall proceed to give some examples of each of these.

In leaving the footprints, I may merely mention that the animals which produced them may, in certain circumstances, have left distinct impressions only of three or four toes, when they actually possessed five, while in other circumstances all may have left marks; and that, when wading in deep mud, their footprints were altogether different from those made on hard sand or clay. In some instances the impressions may have been made by animals wading or swimming in water, while in others the rain marks and sun cracks afford evidence that the surface was a subaërial one. They are chiefly interesting as indicating the wide diffusion and abundance of the creatures producing them, and that they haunted tidal flats and muddy shores, perhaps emerging from the water that they might bask in the sun, or possibly searching for food among the rejectamenta of the sea, or of lagunes and estuaries.

The Labyrinthodonts of the Coal Period, Baphetes Planiceps and Dendrerpeton Acadianum.

In the summer of 1851 I had occasion to spend a day at the Albion Mines in the eastern part of Nova Scotia, and on arriving at the railway station in the afternoon, found myself somewhat too early for the train. By way of improving the time thus left on my hands, I betook myself to the examination of a large pile of rubbish, consisting of shale and ironstone from one of the pits, and in which I had previously found scales and teeth of fishes. In the blocks of hard carbonaceous shale and earthy coal, of which the pile chiefly consisted, scales, teeth and coprolites often appeared on the weathered ends and surfaces as whitish spots. In looking for these, I observed one of much greater size than usual on the edge of a block, and on splitting it open, found a large flattened skull, about six inches broad, the cranial bones of which remained entire on one side of the mass, while the palate and teeth, in several fragments, came away with the other half. Carefully trimming the larger specimen, and gathering all the smaller fragments, I packed them up as safely as possible, and returned from my little excursion much richer than I had hoped.

The specimen, on further examination, proved somewhat puzzling. I supposed it to be, most probably, the head of a large ganoid fish; but it seemed different from anything of this kind with which I could compare it; and at a distance from comparative anatomists, and without sufficient means of determination, I dared not refer it to anything higher in the animal scale. Hoping for further light, I packed it up with some other specimens, and sent it to the Secretary of the Geological Society of London, with an explanatory note as to its geological position, and requesting that it might be submitted to some one versed in such fossils. For a year or two, however, it remained as quietly in the Society's collection as if in its original bed in the coal mine, until attention having been attracted to such remains by the discoveries made by Sir Charles Lyell and myself in 1852, at the South Joggins, and published in 1853,[129] the Secretary or President of the Society re-discovered the specimen, and handed it to Sir Richard Owen, by whom it was described in December, 1853,[130] under the name of _Baphetes planiceps_, which may be interpreted the "flat-headed diving animal," in allusion to the flatness of the creature's skull, and the possibility that it may have been in the habit of diving.

[129] _Journal of Geological Society of London_, vol. ix.

[130] _Journal of Geological Society_, vol. x.; and additional notes, vol. xi.

The parts preserved in my specimen are the bones of the anterior and upper part of the skull in one fragment, and the teeth and palatal bones in others. These parts were carefully examined and described by Owen, and the details will be found in his papers referred to in the note. We may merely observe here that the form and arrangement of the bones showed batrachian affinities, that the surface of the cranium was sculptured in the manner of the group of Labyrinthodonts, and that the teeth possessed the peculiar and complicated plication of the ivory and enamel seen in creatures of this type. The whole of these characters are regarded as allying the animal with the great crocodilian frogs of the Trias of Europe, first known as _Cheirotherians_, owing to the remarkable hand-like impressions of their feet, and afterwards as _Labyrinthodonts_, from the beautifully complicated convolutions of the ivory of their teeth.

Unfortunately the original specimen exhibited only the head, and after much and frequent subsequent searching, the only other bones found are a scapula, or shoulder bone, and one of the surface scales which served for protection, and which indicate at least that the creature possessed walking limbs and was armed with bony scales sculptured in the same manner with the skull bones.

Of the general form and dimensions of _Baphetes_, the facts at present known do not enable us to say much. Its formidable teeth and strong maxillary bones show that it must have devoured animals of considerable size, probably the fishes whose remains are found with it, or the smaller reptiles of the coal. It must, in short, have been crocodilian, rather than frog-like, in its mode of life; but whether, like the Labyrinthodonts, it had strong limbs and a short body, or like the crocodiles, an elongated form and a powerful natatory tail, the remains do not decide. One of the limbs or a vertebra of the tail would settle this question, but neither has as yet been found. That there were large animals of the labyrinthodontal form in the coal period is proved by the footprints discovered by Dr. King in Pennsylvania, which may have been produced by an animal of the type of _Baphetes_, as well as by those of _Sauropus unguifer_ from the Carboniferous of Nova Scotia, and which would very well suit an animal of this size and probable form. On the other hand, that there were large swimming reptiles seems established by the discovery of the vertebræ of _Eosaurus Acadianus_, at the Joggins, by Marsh.[131] The locomotion of _Baphetes_ must have been vigorous and rapid, but it may have been effected both on land and in water, and either by feet or tail, or both. A jawbone found at the Joggins in Nova Scotia, and to which I have attached the name _Baphetes minor_, may have belonged to a second species. Great Batrachians allied to Baphetes, but different specifically or generically, have since been found in the coal formations of Great Britain, the continent of Europe and the United States.

[131] _Silliman's Journal_, 1859.

With the nature of the habitat of this formidable creature we are better acquainted. The area of the Albion Mines coal field was somewhat exceptional in its character. It seems to have been a bay or indentation in the Silurian land, separated from the remainder of the coal field by a high shingle beach, now a bed of conglomerate. Owing to this circumstance, while in the other portions of the Nova Scotia coal field the beds of coal are thin, and alternate with sandstones and shales, at the Albion Mines a vast thickness of almost unmixed vegetable matter has been deposited, constituting the "main seam" of thirty-eight feet thick, and the "deep seam," twenty-four feet thick, as well as still thicker beds of highly carbonaceous shale. But, though the area of the Albion coal measures was thus separated, and preserved from marine incursions, it must have been often submerged, and probably had connection with the sea, through rivers or channels cutting the enclosing beach. Hence beds of earthy matter occur in it, containing remains of large fishes. One of the most important of these is that known as the "Holing stone," a band of black highly carbonaceous shale, coaly matter, and clay ironstone, occurring in the main seam, about five feet below its roof, and varying in thickness from two inches to nearly two feet. It was from this band that the rubbish heap in which I found the skull of _Baphetes planiceps_ was derived. It is a laminated bed, sometimes hard and containing much ironstone, in other places soft and shaly, but always black and carbonaceous, and often with layers of coarse coal, though with few fossil plants retaining their forms. It contains large round flat scales and flattened curved teeth, which I attribute to a fish of the genus _Rhizodus_, resembling, if not identical with, _R. lancifer_, Newberry. With these are double-pointed shark-like teeth, and long cylindrical spines of a species of _Diplodus_, which I have named _D. acinaces.[132]_ There are also shells of the minute _Spirorbis_, so common in the coal measures of other parts of Nova Scotia, and abundance of fragments of coprolitic matter, or fossil excrement, sometimes containing bones and scales of fishes.

[132] "Supplement to Acadian Geology," pp. 43 and 50. These fishes are now known under the generic name Leptacanthus.

It is evident that the "Holing stone" indicates one of those periods in which the Albion coal area, or a large part of it, was under water, probably fresh or brackish, as there are no properly marine shells in this, or any of the other beds of this coal series. We may then imagine a large lake or lagune, loaded with trunks of trees and decaying vegetable matter, having in its shallow parts, and along its sides, dense brakes of _Calamites_, and forests of _Sigillaria_, _Lepidodendron_, and other trees of the period, extending far on every side as damp pestilential swamps. In such a habitat, uninviting to us, but no doubt suited to _Baphetes_, that creature crawled through swamps and thickets, wallowed in flats of black mud, or swam and dived in search of its finny prey. It was, in so far as we know, the monarch of these swamps, though there is, as already stated, evidence of the existence of similar creatures of this type quite as large in other parts of the Nova Scotia coal field. We must now notice a smaller animal belonging to the same family of Labyrinthodonts.

The geology of Nova Scotia is largely indebted to the world-embracing labours of Sir Charles Lyell. Though much had previously been done by others, his personal explorations in 1842, and his paper on the gypsiferous formation, published in the following year, first gave form and shape to some of the more difficult features of the geology of the country, and brought it into relation with that of other parts of the world. In geological investigation, as in many other things, patient plodding may accumulate large stores of fact, but the magic wand of genius is required to bring out the true value and significance of these stores of knowledge. It is scarcely too much to say that the exploration of a few weeks, and subsequent study of the subject by Sir Charles, with the impulse and guidance given to the labours of others, did as much for Nova Scotia as might have been effected by years of laborious work under less competent heads.

Sir Charles naturally continued to take an interest in the geology of Nova Scotia, and to entertain a desire to explore more fully some of those magnificent coast sections which he had but hastily examined; and when, in 1851, he had occasion to revisit the United States, he made an appointment with the writer of these pages to spend a few days in renewed explorations of the cliffs of the South Joggins. The object specially in view was the thorough examination of the beds of the true coal measures, with reference to their contained fossils, and the conditions of accumulation of the coal; and the results were given to the world in a joint paper on "The remains of a reptile and a land shell discovered in the interior of an erect tree in the coal measures of Nova Scotia," and in the writer's paper on the "Coal Measures of the South Joggins";[133] while other important investigations grew out of the following up of these researches, and much matter in relation to the vegetable fossils still remains to be worked up. It is with the more striking fact of the discovery of the remains of a reptile in the coal measures that we have now to do.

[133] _Journal of the Geological Society of London_, vols. ix. and x.; and "Acadian Geology."

The South Joggins Section is, among other things, remarkable for the number of beds which contain remains of erect trees imbedded _in situ_: these trees are for the most part Sigillariæ, those great-ribbed pillar-like trees which seem to have been so characteristic of the forests of the coal formation flats and swamps, and so important contributors to the formation of coal. They vary in diameter from six inches to five feet. They have grown on underclays and wet soils, similar to those on which the coal was accumulated; and these having been submerged or buried by mud carried down by inundations, the trees, killed by the accumulations around their stems, have decayed, and their tops being broken off at the level of the mud or sand, the cylindrical cavities left open by the disappearance of the wood, and preserved in their form by the greater durability of the bark, have been filled with sand and clay. This, now hardened into stone, constitutes pillar-like casts of the trees, which may often be seen exposed in the cliffs, and which, as these waste away, fall upon the beach. The sandstones enveloping these pillared trunks of the ancient Sigillariæ of the coal, are laminated or bedded, and the laminæ, when exposed, split apart with the weather, so that the trees themselves become broken across; this being often aided by the arrangement of the matter within the trunks, in layers more or less corresponding to those without. Thus one of these fossil trees usually falls to the beach in a series of discs, somewhat resembling the grindstones which are extensively manufactured on the coast. The surfaces of these fragments often exhibit remains of plants which have been washed into the hollow trunks, and have been imbedded there; and in our explorations of the shore, we always carefully scrutinized such specimens, both with the view of observing whether they retained the superficial markings of Sigillariæ, and with reference to the fossils contained in them. It was while examining a pile of these "fossil grindstones" that we were surprised by finding on one of them what seemed to be fragments of bone. On careful search other bones appeared, and they had the aspect, not of remains of fishes, of which many species are found fossil in these coal measures, but rather of limb bones of a quadruped. The fallen pieces of the tree were carefully broken up, and other bones disengaged, and at length a jaw with teeth made its appearance. We felt quite confident, from the first, that these bones were reptilian; and the whole, being carefully packed and labelled, were taken by Sir Charles to the United States, and submitted to Prof. J. Wyman of Cambridge; who recognised their reptilian character, and prepared descriptive notes of the principal bones, which appeared to have belonged to two species. He also observed among the fragments an object of different character, apparently a shell; which was recognised by Dr. Gould of Boston, and afterward by M. Deshayes, as probably a land-snail, and has since been named _Pupa vetusta_.

The specimens were subsequently taken to London and reexamined by Prof. Owen, who confirmed Wyman's inferences, added other characters to the description, and named the larger and better preserved species _Dendrerpeton Acadianum_, in allusion to its discovery in the interior of a tree, and to its native country of Acadia or Nova Scotia. It is necessary to state in explanation of the fragmentary character of the remains obtained, that in the decay of the animals imbedded in the erect trees at the Joggins, their skeletons have become disarticulated, and the portions scattered, either by falling into the interstices of the vegetable fragments in the bottom of the hollow trunks, or by the water with which these may have sometimes been partly filled. We thus usually obtain only separate bones; and though all of these are no doubt present in each case, it is often impossible in breaking up the hard matrix to recover more than a portion of them. The original description by Owen was therefore based on somewhat imperfect material, but additional specimens subsequently found have supplemented it in such a manner as to enable us somewhat completely to restore in imagination the form of the animal, which, though much smaller than _Baphetes_, agrees with it in its sculptured bones, in its bony armature, especially beneath, and in its plicated teeth.

The specimen illustrates the sculptured bones of Dendrerpeton and its plaited teeth, as well as large size and massive development of the arm bone.]

In form, _Dendrerpeton Acadianum_ was probably lizard-like; with a broad flat head, short stout limbs and an elongated tail; and having its skin, and more particularly that of the belly, protected by small bony plates closely overlapping each other, and arranged _en chevron_, in oblique rows meeting on the mesial line, where in front was a thoracic plate. It may have attained the length of two feet. The form of the head is not unlike that of _Baphetes_, but longer in proportion; and much resembles that of the labyrinthodont reptiles of the Trias. The bones of the skull are sculptured as in Baphetes, but in a smaller pattern.

The fore limb of the adult animal, including the toes, must have been four or five inches in length, and is of massive proportions. The bones were hollow, and in the case of the phalanges the bony walls were thin, so that they are often crushed flat. The humerus, or arm bone, however, was a strong bone, with thick walls and a cancellated structure toward its extremities; still even these have sometimes yielded to the great pressure to which they have been subjected. The cavity of the interior of the limb bones is usually filled with calc-spar stained with organic matter, but showing no structure; and the inner side of the bony wall is smooth without any indication of cartilaginous matter lining it.

The vertebræ, in the external aspect of their bodies, remind one of those of fishes, expanding toward the extremities, and being deeply hollowed by conical cavities, which appear even to meet in the centre. There is, however, a large and flattened neural spine. The vertebræ are usually much crushed, and it is almost impossible to disengage them from the stone. The ribs are long and curved, showing a reptilian style of chest. The posterior limb seems to have been not larger than the anterior, perhaps smaller. The tibia, or principal bone of the fore leg is much flattened at the extremity, as in some Labyrinthodonts, and the foot must have been broad, and probably suited for swimming, or walking on soft mud, or both. That the hind limb was adapted for walking is shown, not merely by the form of the bones, but also by that of the pelvis.

The external scales are thin, oblique-rhomboidal or elongated-oval, marked with slight concentric lines, but otherwise smooth, and having a thickened ridge or margin, in which they resemble those of Archegosaurus, and also those of _Pholidogaster pisciformis_, described by Huxley from the Edinburgh coal field,--an animal which indeed appears in most respects to have a close affinity with _Dendrerpeton_. The microscopic structure of the scales is quite similar to that of the other bones, and different from that of the scales of ganoid fishes, the shape of the cells being batrachian. For other particulars of its structure reference may be made to the papers named at the end of the chapter.

With respect to the affinities of the creature, I think it is obvious that it is most nearly related to the group of Lahyrinthodonts, and that it has the same singular mixture of batrachian and reptilian characters which distinguish these ancient animals, and which give them the appearance of prototypes of the reptilian class. A second and smaller species of Dendrerpeton was subsequently obtained at the Joggins, and others have been found, more especially by Fritsch, in the Carboniferous and Permian of Europe.

This ancient inhabitant of the coal swamps of Nova Scotia was, in short, as we often find to be the case with the earliest forms of life, the possessor of powers and structures not usually, in the modern world, combined in a single species. It was certainly not a fish, yet its bony scales and the form of its vertebræ, and of its teeth, might, in the absence of other evidence, cause it to be mistaken for one. We call it a Batrachian, yet its dentition, the sculpturing of the bones of its skull, which were certainly no more external plates than the similar bones of a crocodile, its ribs, and the structure of its limbs, remind us of the higher reptiles; and we do not know that it ever possessed gills, or passed through a larval or fish-like condition. Still, in a great many important characters, its structures are undoubtedly batrachian. It stands, in short, in the same position with the _Lepidodendra_ and _Sigillariæ_ under whose shade it crept, which, though placed by palæobotanists in alliance with certain modern groups of plants, manifestly differed from these in many of their characters, and occupied a different position in nature. In the coal period the distinctions of physical and vital conditions were not well defined. Dry land and water, terrestrial and aquatic plants and animals, and lower and higher forms of animal and vegetable life, are consequently not easily separated from each other. This is no doubt a state of things characteristic of the earlier stages of the earth's history, yet not necessarily so; for there are some reasons, derived from fossil plants, for believing that in the preceding Devonian period there was less of this, and consequently that there may then have been a higher and more varied animal life than in the coal period.[134]

[134] See the author's paper on Devonian plants, _Journal of the Geological Society_, vol. xviii. p. 328.

The dentition of _Dendrerpeton_ shows it to have been carnivorous in a high degree. It may have captured fishes and smaller reptiles, either on land or in water, and very probably fed on dead carcases as well. If, as seems likely, any of the footprints referred to previously belong to this animal, it must have frequented the shores, either in search of garbage, or on its way to and from the waters. The occurrence of its remains in the stumps of Sigillaria, with land snails and millipedes, shows also that it crept in the shade of the woods in search of food; and in noticing coprolitic matter, in a subsequent page, I shall show that remains of excrementitious substances, probably of this species, contain fragments attributable to smaller reptiles, and other animals of the land.

All the bones of _Dendrerpeton_ hitherto found, as well as those of the smaller reptilian species hereafter described, have been obtained from the interior of erect Sigillariæ, and all of these in one of the many beds, which, at the Joggins, contain such remains. The thick cellular inner bark of Sigillaria was very perishable; the slender woody axis was somewhat more durable; but near the surface of the stem, in large trunks, there was a layer of elongated cells, or bast tissue, of considerable durability, and the outer bark was exceedingly dense and indestructible.[135] Hence an erect tree, partly imbedded in sediment, and subjected to the influence of the weather, became a hollow shell of bark; in the bottom of which lay the decaying remains of the woody axis, and shreds of the fibrous bark. In ordinary circumstances such hollow stems would be almost immediately filled with silt and sand, deposited in the numerous inundations and subsidences of the coal swamps. Where, however, they remained open for a considerable time, they would constitute a series of pitfalls, into which animals walking on the surface might be precipitated; and being probably often partly covered by remains of prostrate trunks, or by vegetation growing around their mouths, they would be places of retreat and abode for land snails and such creatures. When the surface was again inundated or submerged, all such animals, with the remains of those which had fallen into the deeper pits, would be imbedded in the sediment which would then fill up the holes. These seem to have been the precise conditions of the bed which has afforded all these remains.

[135] See a paper by the author, on the Structures of Coal, _Journal of the Geological Society_, vol. xv.; also "Supplement to Acadian Geology."

This is a sketch of a tree which afforded remains of Dendrerpeton, Pupæ, etc.]

The history of a bed containing reptiliferous erect trees would thus be somewhat as follows:--

A forest or grove of the large-ribbed trees known as _Sigillariæ_, was either submerged by subsidence, or, growing on low ground, was invaded with the muddy waters of an inundation, or successive inundations, so that the trunks were buried to the depth of several feet. The projecting tops having been removed by subaërial decay, the buried stumps became hollow, while their hard outer bark remained intact. They thus became hollow cylinders in a vertical position, and open at top. The surface having then become dry land, covered with vegetation, was haunted by small quadrupeds and other land animals, which from time to time fell into the open holes, in some cases nine feet deep, and could not extricate themselves. On their death, and the decomposition of their soft parts, their bones and other hard portions remained in the bottom of the tree intermixed with any vegetable _débris_ or soil washed in by rain, and which formed thin layers separating successive animal deposits from each other. Finally, the area was again submerged or overflowed by water, bearing sand and mud. The hollow trees were filled to the top, and their animal contents thus sealed up. At length the material filling the trees was by pressure and the access of cementing matter hardened into stone, not infrequently harder than that of the containing beds, and the whole being tilted to an angle of 20°, and elevated into land exposed to the action of the tides and waves, these singular coffins present themselves as stony cylinders projecting from the cliff or reef, and can be extracted and their contents studied.

The singular combination of accidents above detailed was, of course, of very rare occurrence, and in point of fact we know only one set of beds at the South Joggins in which such remains so preserved occur; nor is there, so far as I am aware, any other known instance elsewhere. Even in the beds in question only a portion of the trees, about fifteen in thirty, have afforded animal remains. We have, however, thus been enabled to obtain specimens of a number of species which would probably otherwise have been unknown, being less likely than others to be preserved in properly aqueous deposits. Such discoveries, on the one hand impress us with the imperfection of the geological record; on the other, they show us the singular provisions which have been made in the course of geological time for preserving the relics of the ancient world, and which await the industry and skill of collectors to disclose their hidden treasures.

I may add that I believe all the trees, about thirty in number, which have become exposed in this bed since its discovery, have been ransacked for such remains; and that while the majority have afforded some reward for the labour, some have been far more rich than others in their contents. It is also to be observed that owing to the mode of accumulation of the mass filling the trees, the bones are usually found scattered in every position, and those of different species intermingled; and that being often much more friable than the matrix, much labour is required for their development; while after all has been done, the result is a congeries of fragments. A few specimens only have been found, showing skeletons complete, or nearly so, and I shall endeavour to figure one or two of these by way of illustration in the present chapter.

The beds on a level with the top of the reptiliferous erect trees are arenaceous sandstones, with numerous erect _Calamites_. I have searched the surfaces of these beds in vain for bones or footprints of the reptiles which must have traversed them, and which, but for hollow erect trees," would apparently have left no trace of their existence. On a surface of similar character, sixty feet higher, and separated by three coals, with their accompaniments, and a very thick compact sandstone, I observed a series of footprints, which may be those of _Dendrerpeton_ or _Hylonomus_.

Species of Microsauria. Hylonomus Lyelli.

In the original reptiliferous tree discovered by Sir C. Lyell and the writer, at the Joggins, in 1851, there were, beside the bones of _Dendrerpeton Acadianum_, some small elongated vertebræ, evidently of a different species. These were first detected by Prof. Wyman, in his examination of these specimens, and were figured, but not named, in the original notice of the specimens. In a subsequent visit to the Joggins I obtained from another erect stump many additional remains of these smaller reptiles, and, on careful comparison of the specimens, was induced to refer them to three species, all apparently generically allied. I proposed for them the generic name _Hylonomus_, "forest dweller." They were described in the Proceedings of the Geological Society for 1859, with illustrations of the teeth and other characteristic parts.[136] The smaller species first described I named _H. Wymani_; the next in size, that to which this article refers, and which was represented by a larger number of specimens, I adopted as a type of the genus, and dedicated to Sir Charles Lyell. The third and largest, represented only by a few fragments of a single skeleton, was named _H. aciedentatus_. This I had subsequently to remove to a new genus, _Smilerpeton_.

[136] _Journal of Geological Society_, vol. xvi.

_Hylonomus Lyelli_ was an animal of small size. Its skull is about an inch in length, and its whole body, including the tail, could not have been more than six or seven inches, long. The bones appear to have been thin and easily separable; and even when they remain together, are so much crushed as to render the shape of the skull not easily discernible. They are smooth on the outer surface to the naked eye; and under a lens show only delicate, uneven striæ and minute dots. They are more dense and hard than those of _Dendrerpeton_, and the bone-cells are more elongated in form. The bones of the snout would seem to have been somewhat elongated and narrow. A specimen in my possession shows the parietal and occipital bones, or the greater part of them, united and retaining their form. We learn from them that the brain case was rounded, and that there was a parietal foramen. There would seem also to have been two occipital condyles, as in modern Batrachians. Several well-preserved specimens of the maxillary and mandibular bones have been obtained. They are smooth, or nearly so, like those of the skull, and are furnished with numerous sharp, conical teeth, anchylosed to the jaw, in a partial groove formed by the outer ridge of the bone. In the anterior part of the lower jaw there is a group of teeth larger than the others. The total number of teeth in each ramus of the lower jaw was about forty, and the number in each maxillary bone about thirty. The teeth are perfectly simple, hollow within, and with very fine radiating tubes of ivory. The vertebræ have the bodies cylindrical or hour-glass shaped, covered with a thin, hard, bony plate, and having within a cavity of the form of two cones, attached by the apices. This cavity was completely surrounded by bone, as it is filled with stained calc-spar in the same manner as the cavities of the limb bones. It was probably occupied by cartilage. The vertebræ were apparently bi-concave, and are furnished with upper and lateral processes similar to those of small lacertian animals. The ribs are long, curved, and at the proximal end have a shoulder and neck. They are hollow, with thin hard bony walls. The anterior limb, judging from the fragment procured, seems to have been slender, with long toes, four or possibly five in number. The posterior limb was longer and stronger, and attached to a pelvis so large and broad as to give the impression that the creature enlarged considerably in size toward the posterior extremity of the body, and that it may have been in the habit of sitting erect. The thigh bone is large and well-formed, with a distinct head and trochanter, and the lower extremity flattened and moulded into two articulating surfaces for the tibia and fibula, the fragments of which show that they were much shorter. The toes of the hind feet have been seen only in detached joints. They seem to have been thicker than those of the fore foot. Detached vertebræ, which seem to be caudal, have been found, and show that the tail was long and probably not flattened. The limb bones are usually somewhat crushed and flattened, especially at their articular extremities, and this seems to have led to the error of supposing that this flattened form was their normal condition; there can be no doubt, however, that it is merely an effect of pressure. The limb bones present in cross section a wall of dense bone with elongated bone-cells, surrounding a cavity now filled with brown calc-spar, and originally occupied with cartilage or marrow. I desire to specify the above points because I believe that most of the creatures referred by Fritsch, Credner, and other European naturalists to the Microsauria are of inferior grade to Hylonomus, though admitted to present points of approximation to the true reptiles. Woodward has recently described the remains of a Microsaurian from the English coal formation. Nothing is more remarkable in the skeleton of this creature than the contrast between the perfect and beautiful forms of its bones, and their imperfectly ossified condition, a circumstance which raises the question whether these specimens may not represent the young of some reptile of larger size.

The dermal covering of this animal is represented in part by oval bony scales, which are so constantly associated with its bones that I can have no doubt that they belonged to it, being, perhaps, the clothing of its lower or abdominal parts. But the most remarkable and unexpected feature of this little creature was the beautiful and ornate scaly covering of its back and sides. Modern Batrachians are characteristically naked, and though we know that some fossil species had coverings below of bony scales, these seemed rather to ally them with bony fishes. One of the specimens of Hylonomus had associated with it a quantity of crumpled shining skin, black and carbonaceous, and which may perhaps have been tanned and so preserved by the water filling the hollow tree impregnated with solution of tannin from the bark. This skin was covered with minute overlapping scales, which, under the microscope, showed the structure of horn rather than of bone. Besides these ordinary scales there were bony prominences, like those of the horned frog, on the back and shoulders, and a species of epaulettes made of long horny bristles curved downward, and apparently placed at the edges of the shoulders. Besides these there were in front and at the side rows of pendants or lappets, all no doubt ornamented with colouring, though now perfectly black. It may be asked what was the use of the ornate covering, and perhaps the question raises that perplexing problem, of the use of beauty in a world where there were no animals with higher æsthetic faculties than those of Batrachians. Scudder suggests a somewhat prosaic use in supposing them to be an armour against the venomous scorpions which were the contemporaries of these little reptiles, and some of them almost as large in size. But the word "venomous" raises another question, for we only infer that the scorpions were venomous from modern analogy and traces of an inflated joint at the end of the tail in some specimens. We have no absolute certainty that the subtle and complex organic poison of the scorpion, and his beautiful injection syringe for placing it under the skin, were perfected at this early time. Thus we have in the far back Carboniferous age a creature as elaborately ornamented and protected as any of the modern lizards, and this, let it be observed, constitutes another and important departure from that batrachian type to which these animals are supposed to conform. I may add here that subsequently portions of skin were found, which from their size probably belonged to _Dendrerpeton_, and that these also were scaly and had lappets, though they did not appear to have the horny tubercles and fringes. It may be asked why such advanced characters should be found in Nova Scotia alone. The answer is that the circumstances of preservation in the erect trees were peculiar, and that only animals of purely terrestrial habits could find access to them, whereas the remains of reptiles found in the Carboniferous elsewhere are in aqueous beds in which aquatic forms were more likely to be preserved, and in which all the soft parts were certain to perish.