_THE OLDEST AIR-BREATHERS._
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.
[Illustration: Footprints of _Hylopus Logani_, Dawson, Lower
Carboniferous, Nova Scotia.
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.
[Illustration: Humerus and Mandibles of Dendrerpeton Acadianum. Natural
size, with one of the teeth enlarged. (From a Photograph.)
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."
[Illustration: A reptiliferous Tree _in situ_, South Joggins, N. Scotia.
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_.
[Illustration: A typical Carboniferous Microsaurian, _Hylonomus Lyelli_
Restoration showing dermal armour and ornaments. Skeleton restored from
measurements of the bones of the type specimen figured at the beginning
of the chapter.]
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.
It is evident from the remains thus described, that we have in
_Hylonomus Lyelli_ an animal of lacertian form, with large and stout
hind limbs, and somewhat smaller fore limbs, capable of walking and
running on land; and though its vertebræ were imperfectly ossified
externally, yet the outer walls were sufficiently strong, and their
articulation sufficiently firm, to have enabled the creature to
erect itself on its hind legs, or to leap. They were certainly
proportionately larger and much more firmly knit than those of
_Dendrerpeton_. Further, the ribs were long and much curved, and imply
a respiration of a higher character than that of modern Batrachians,
and consequently a more highly vitalized muscular system. If to these
structural points we add the somewhat rounded skull, indicating a large
brain, we have before us a creature which, however puzzling in its
affinities when anatomically considered, is clearly not to be ranked
as low in the scale of creation as modern tailed Batrachians, or even
as the frogs and toads. We must add to these also, as important points
of difference, the bony scales with which it was armed below, and the
ornate apparatus of horny appendages, with which it was clad above.
These last, as described in the last section, show that this little
animal was not a squalid, slimy dweller in mud, like _Menobranchus_
and its allies, but rather a beautiful and sprightly tenant of the
coal-formation thickets, vying in brilliancy, and perhaps in colouring,
with the insects which it pursued and devoured. Remains of as many
as eight or ten individuals have been obtained from three erect
Sigillariæ, indicating that these creatures were quite abundant, as
well as active and terrestrial in their mode of life.
With respect to the affinities of this species, I think it is
abundantly manifest that it presents no close relationship with any
reptile hitherto discovered in the Carboniferous system, except perhaps
some of the smaller forms in the Permian of Europe, with which Credner
and Fritsch have compared it. It is scarcely necessary to say that
the characters above described entirely remove this animal from the
Labyrinthodonts. Equal difficulties attend the attempt to place it in
any other group of recent or extinct Batrachians or proper reptiles.
The structures of the skull, and of some points in the vertebræ,
certainly resemble those of Batrachians; but, on the other hand,
the well-developed ribs, evidently adapted to enlarge the chest in
respiration, the pelvis, and the cutaneous covering, are unexampled in
modern Batrachians, and assimilate the creature to the true lizards.
I have already, in my original description of the animal in 1859,
expressed my belief that _Hylonomus_ may have had lacertian affinities,
but I do not desire to speak too positively in this matter;[137] and
shall content myself with stating the following alternatives as to
the probable relations of these animals, (1) They may have been true
reptiles of low type, and with batrachian tendencies. (2) They may have
been representatives of a new family of Batrachians, exhibiting in some
points lacertian affinities. (3) They may have been the young of some
larger reptile, too large and vigorous to be entrapped in the pitfalls
presented by the hollow Sigillaria stumps, and in its adult state
losing the batrachian peculiarities apparent in the young. Whichever of
these views we may adopt, the fact remains, that in the structure of
this curious little creature we have peculiarities both batrachian and
lacertian, in so far as our experience of modern animals is concerned.
It would, however, accord with observed facts in relation to other
groups of extinct animals, that the primitive Batrachians of the
coal period should embrace in their structures points in after times
restricted to the true reptiles. On the other hand, it would equally
accord with such facts that the first-born of Lacertians should lean
towards a lower type, by which they may have been preceded. My present
impression is, that they may constitute a separate family or order, to
which I would give the name of Microsauria, and which may be regarded
as allied, on the one hand, to certain of the humbler lizards, as the
Gecko or Agama, and, on the other, to the tailed Batrachians.
[137] I am glad to say that Fritsch and Credner now lean to the same
view.
It is likely that _Hylonomus Lyelli_ was less aquatic in its habits
than _Dendrerpeton_, Its food consisted, apparently, of insects and
similar creatures. The teeth would indicate this, and near its bones
there are portions of coprolite, containing remains of insects and
myriapods. It probably occasionally fell a prey to _Dendrerpeton_, as
bones, which may have belonged either to young individuals of this
species or to its smaller congener _H. Wymani_, are found in larger
coprolites, which may be referred with probability to _Dendrerpeton
Acadianum_. This coprolitic matter, which is somewhat plentiful on
some of the surfaces in the erect trees, also informs us that the
imprisoned animals may in some cases have continued to live for some
time, feeding on such animals as may have fallen into their place of
confinement, which was destined also to be their tomb. Some other
points of interest appear on the examination of this excrementitious
matter. It contains much carbonate of lime, indicating that snails or
other mollusks furnished a considerable part of the food of the smaller
reptiles. Some portions of it are filled with chitinous fragments,
parts of millipedes or insects, but usually so broken up as scarcely to
be distinguishable. One curious exception was a part of the head of an
insect containing a portion of one of its eyes. The facets of this can
be readily seen with the microscope, and are similar to those of modern
cockroaches. About 250 of these little eyes are discernible, and they
must have been much more numerous. Two points are of interest here:
First, the perfection of the compound eye for vision in air. It had
long before, in the case of the Trilobites, been used for seeing under
water. Secondly, the great age of the still ubiquitous and aggressive
family of the cockroaches. In point of fact the oldest known insect,
the Protoblattina of the Silurian, is one of these creatures, and they
are the most abundant insects in the Carboniferous, so that if they now
dispute with us the possession of our food, they may at least put in
the claim of prior occupancy of the world. In one mass a quantity of
thickish crust or shell appears, which under the microscope presents a
minutely tubular and laminated appearance. It may have belonged to some
small crustacean or large scorpion on which a _Dendrerpeton_ may have
been feeding before it fell into the pit in which it was entombed.
[Illustration: _Dolichosoma longissimum_, a serpentiform Permian
Batrachian after Fritsch. This and Hylonomus are opposite or extreme
types in regard to general form.]
In addition to the reptilian species above noticed, the erect trees of
Coal Mine Point have afforded several others. There is a second and
smaller species of Dendrerpeton (_D. Oweni_) and other forms belonging
to the group of Microsauria of which Hylonomus is the type. A second
species of that genus (_H. Wymani_) has already been mentioned. A
similar creature, but of larger size and with teeth of a wedge or
chisel shape, has been referred to a distinct genus, _Smilerpeton_. It
seems to have been rare, and the only skeleton found is very imperfect.
Its teeth are of a form that may have served even for vegetable food,
as their sharp edges must have had considerable cutting power. Another
curious form of tooth appears in the genus _Hylerpeton_. It has the
points worked into oblique grooves separated by sharp edges, which
must have greatly aided in piercing tough integument. These creatures
seem to have been of stout and robust build, with large limbs. Still
another generic type (_Fritschia_) is represented by a species near to
Hylonomus in several respects, and with long and beautifully formed
limb bones, but with the belly protected with rod-like bodies instead
of scales. In this respect Hylerpeton is somewhat intermediate, having
long and narrow scales on the belly instead of the oval or roundish
scales of Hylonomus. All these last-mentioned forms are Microsaurians,
with simple teeth and well-developed ribs and limbs, and smooth
cranial bones. Two other species are represented by portions of single
skeletons too imperfect to allow them to be certainly determined.
I would emphasize here that the vertebrate animals found in the erect
trees are necessarily a selection from the most exclusively terrestrial
forms, and from the smaller species of these. The numerous newt-like
and serpentiform species found in the shales of the coal formation
could not find access to these peculiar repositories, nor could the
larger species of the Labyrinthodonts and their allies, even if they
were in the habit of occasionally prowling in the forests in search of
prey, and this would scarcely be likely, more especially as the waters
must have afforded to them much more abundant supplies of food. Of
the numerous species figured by Fritsch, Cope and Huxley, only a few
approach very near to the forms entrapped in the old hollow Sigillariæ,
though several have characters half batrachian and half reptilian.
Invertebrate Air-breathers.
The coal formation rocks have afforded Land Snails, Millipedes,
Spiders, Scorpions and Insects, so that all the great types of
invertebrate life which up to this day can live on land already had
representatives in this ancient period. Some of them, indeed, we can
trace further back, the land snails probably to the Devonian, the
Millipedes to the same period, and the Scorpions and insects as far as
the Silurian. No land vertebrate is yet known, older than the Lower
Carboniferous, but there is nothing known to us in physical condition,
to preclude the existence of such creatures at least in the Devonian.
It would take us too far afield to attempt to notice the invertebrate
land life of the Palæozoic in general. This has been done in great
detail by Dr. Scudder. I shall here limit myself to the animals found
in our erect trees, and merely touch incidentally on such others as may
be connected with them.
I have already mentioned the occurrence of a land-snail, a true
pulmonate mollusk, in the first find by Lyell and myself at Coal Mine
Point, and this was the first animal of this kind known in any rocks
older than the Purbeck formation of England. It is one of the groups
of so-called Chrysalis-shells, scarcely distinguishable at first
sight from some modern West Indian species, and distinctly referable
to the modern genus Pupa. It was named _Pupa vetusta_, and a second
and smaller species subsequently found was named _P. Bigsbyi_, and a
third of different form, and resembling the modern snails, bears the
name _Zonites priscus_. The only other Palæozoic land mollusks known
at present are a few species found in the coal formation of Ohio, and
a fragment supposed to indicate another species from the Devonian
plant-beds of St. John's, New Brunswick. This last is the oldest known
evidence of pulmonate snails. If we ask the precise relations of these
creatures to modern snails, it may be answered that of the two leading
subdivisions of the group of air-breathing snails (_Pulmonifera_), the
Operculate, or those with a movable plate to close the mouth of the
shell, and the Inoperculate, or those that are destitute of any such
shelly lid or operculum to close the shell, the first has been traced
no farther back than the Eocene. The second or inoperculate division,
includes some genera that are aquatic and some that are terrestrial.
Of the aquatic genera no representatives are known in formations
older than the Wealden and Purbeck, and these only in Europe. The
terrestrial group, or the family of the _Helicidæ_, which, singularly
enough, is that which diverges farthest from the ordinary gill-bearing
Gasteropods, is the one which has been traced farthest back, and
includes the Palæozoic species. It is further remarkable that a very
great gap exists in the geological history of this family. No species
are known between the Carboniferous and the early Tertiary, though in
the intervening formations there are many fresh-water and estuarine
deposits in which such remains might be expected to occur. There is
perhaps no reason to doubt the continuance of the Helicidæ through
this long portion of geological time, though it is probable that
during the interval the family did not increase much in the numbers
of its species, more especially as it seems certain that it has its
culmination in the modern period, where it is represented by very many
and large species, which are dispersed over nearly all parts of our
continents.
[Illustration: Carboniferous Land Snails.
_Pupa vetusta_, Dawson, and _Conulus priscus_, Carpenter, with egg of
_Pupa vetusta_--the whole considerably magnified.]
[Illustration: I published in 1880, in the _American Journal of
Science_, a fragment of what seemed to be a land-snail, from the Middle
Erian plant-beds of St. John, New Brunswick (_Strophia grandava_,
figured here), but have mentioned it with some doubt in the text. Mr.
G. F. Matthew has, however, recently communicated to the Royal Society
of Canada a second species, found by Mr. W. I. Wilson in the same beds,
and which he names _Pupa primava_. It is accompanied with a scorpion
and a millipede. Thus the existence of Land Snails of the Pupa type in
the Devonian may be considered as established.]
The mode of occurrence of the Palæozoic Pulmonifera in the few
localities where they have been found is characteristic. The earliest
known species, _Pupa vetusta_, was found, as already stated, in the
material filling the once hollow stem of a Sigillaria at the South
Joggins in Nova Scotia, and many additional specimens have subsequently
been obtained from similar repositories in the same locality,
where they are associated with bones of Batrachians and remains of
Millipedes. Other specimens, and also the species _Zonites priscus_,
have been found in a thin, shaly layer, containing _débris_ of plants
and crusts of Cyprids, and which was probably deposited at the outlet
of a small stream flowing through the coal-formation forest. The two
species found in Illinois occur, according to Bradley, in an underclay
or fossil soil which may have been the bed of a pond or estuary, and
subsequently became a forest subsoil. The Erian .species occurs in
shales charged with remains of land plants, and which must consequently
have received abundant drainage from neighbouring land. It is only
in such deposits that remains of true land snails can be expected to
occur; though, had fresh-water or brackish water Pulmonates abounded
in the Carboniferous age, their remains should have occurred in those
bituminous and calcareo-bituminous shales which contain such vast
quantities of _débris_ of Cyprids, Lamellibranchs and fishes of the
period, mixed with fossil plants.
The specimen first obtained in 1887 having been taken by Sir Charles
Lyell to the United States, and submitted to the late Prof. Jeffries
Wyman, the shell in question was recognised by him and the late Dr.
Gould, of Boston, as a land shell. It was subsequently examined by M.
Deshayes and Mr. Gwyn Jeffries, who concurred in this determination;
and its microscopic structure was described by the late Prof. Quekett,
of London, as similar to that of modern land shells. The single
specimen obtained on this occasion was somewhat crushed, and did
not show the aperture. Hence the hesitation as to its nature, and
the delay in naming it, though it was figured and described in the
paper above cited in 1852. Better specimens showing the aperture were
afterward obtained by the writer, and it was named and described by
him in his "Air-breathers of the Coal Period," in 1863. Owen, in his
"Palæontology," subsequently proposed the generic name _Dendropupa_.
This I have hesitated to accept, as expressing a generic distinction
not warranted by the facts; but should the shell be considered to
require a generic or sub-generic distinction, Owen's name should be
adopted for it. There seems, however, nothing to prevent it from being
placed in one of the modern sub-genera of simple-lipped Pupæ. With
regard to the form of its aperture, I may explain that some currency
has been given to an incorrect representation of it, through defective
specimens. In the case of delicate shells like this, imbedded in a hard
matrix, it is of course difficult to work out the aperture perfectly;
and in my published figure in the "Air-breathers," I had to restore
somewhat the broken specimens in my possession. This restoration,
specimens subsequently found have shown to be very exact.
As already stated, this shell seems closely allied to some modern Pupæ.
Perhaps the modern species which approaches most nearly to it in form,
markings and size, is _Macrocheilus Gossei_ from the West Indies,
specimens of which were sent to me some years ago by Mr. Bland, of New
York, with the remark that they must be very near to my Carboniferous
species. Such edentulous species as _Pupa (Leucochila) fallax_ of
Eastern America very closely resemble it; and it was regarded by the
late Dr. Carpenter as probably a near ally of those species which are
placed by some European conchologists in the genus _Pupilla_.
_Pupa vetusta_ has been found at three distinct levels in the coal
formation of the South Joggins. The lowest is the shale above referred
to. The next, 1,217 feet higher, is that of the original discovery.
The third, 800 feet higher, is in an erect Sigillaria holding no
other remains. Thus, this shell has lived in the locality at least
during the accumulation of 2,000 feet of beds, including a number of
coals and erect forests, as well as beds of bituminous shales and
calcareo-bituminous shale, the growth of which must have been very slow.
In the lowest of these three horizons the shells are found, as already
stated, in a thin bed of concretionary clay of dark grey colour,
though associated with reddish beds. It contains _Zonites priscus_ as
well, though this is very rare, and there are a few valves of _Cythere_
and shells of _Naiadites_ as well as carbonaceous fragments, fronds of
ferns, _Trigonocarpa_, etc. The _Pupæ_ are mostly adult, but many very
young shells also occur, as well as fragments of broken shells. The bed
is evidently a layer of mud deposited in a pond or creek, or at the
mouth of a small stream. In modern swamps multitudes of fresh-water
shells occur in such places, and it is remarkable that in this case
the only Gasteropods are land shells, and these very plentiful, though
only in one bed about an inch in thickness. This would seem to imply
an absence of fresh-water Pulmonifera. In the erect _Sigillariæ_ of
the second horizon the shells occur either in a sandy matrix, more or
less darkened with vegetable matter, or in a carbonaceous mass composed
mainly of vegetable _débris_. Except when crushed or flattened, the
shells in these repositories are usually filled with brownish calcite.
From this I infer that most of them were alive when imbedded, or at
least that they contained the bodies of the animals; and it is not
improbable that they sheltered themselves in the hollow trees, as is
the habit of many similar animals in modern forests. Their residence
in these trees, as well as the characters of their embryology, are
illustrated by the occurrence of their mature ova. One of those, which
I have considered worth figuring, has been broken in such a way as to
show the embryo shell.
They may also have formed part of the food of the reptilian animals
whose remains occur with them. In illustration of this I have elsewhere
stated that I have found as many as eleven unbroken shells of _Physa
heterostropha_ in the stomach of a modern _Menobranchus_. I think it
certain, however, that both the shells and the reptiles occurring in
these trees must have been strictly terrestrial in their habits, as
they could not have found admission to the erect trees unless the
ground had been sufficiently dry to allow several feet of the imbedded
hollow trunks to be free from water. In the highest of the three
horizons the shells occurred in an erect tree, but without any other
fossils, and they had apparently been washed in along with a greyish
mud.[138]
[138] The discovery of the shells in this tree was made by Albert I.
Hill, C.E. The tree is in Group XXVI. of Division 4 of my Joggins
section. The original reptiliferous trees are in Group XV., and the
lowest bed in Group VIII.
If we exclude the alleged _Palæorbis_ referred to below, all the
Palæozoic Pulmonifera hitherto found are American. Since, however, in
the Carboniferous age, Batrachians, Arachnidans, Insects and Millipedes
occur on both continents, it is not unlikely that ere long European
species of land snails will be announced The species hitherto found
in Eastern America are in every way strangely isolated. In the plant
beds of St. John, about 9,000 feet in thickness, and in the coal
formation of the South Joggins, more than 7,000 feet in thickness,
no other Gasteropods occur, nor, I believe, do any occur in the beds
holding land snails in Illinois. Nor, as already stated, are any of
the aquatic Pulmonifera known in the Palæozoic. Thus, in so far as
at present known, these Palæozoic snails are separated not only from
any predecessors, if there were any, or successors, but from any
contemporary animals allied to them.
It is probable that the land snails of the Erian and Carboniferous
were neither numerous nor important members of the faunas of those
periods. Had other species existed in any considerable numbers, there
is no reason why they should not have been found in the erect trees,
or in those shales which contain land plants. More especially would
the discovery of any larger species, had they existed, been likely to
have occurred. Further, what we know of the vegetation of the Palæozoic
period would lead us to infer that it did not abound in those
succulent and nutritious leaves and fruits which are most congenial
to land snails. It is to be observed, however, that we know little as
yet of the upland life of the Erian or Carboniferous. The animal life
of the drier parts of the low country is indeed as yet very little
known; and but for the revelations in this respect of the erect trees
in one bed in the coal formation of Nova Scotia, our knowledge of the
land snails and Millipedes, and also of an eminently terrestrial group
of reptiles, the _Microsauria_, would have been much more imperfect
than it is. We may hope for still further revelations of this kind,
and in the meantime it would be premature to speculate as to the
affinities of our little group of land snails with animals either their
contemporaries or belonging to earlier or later formations, except to
note the fact of the little change of form or structure in this type
of life in that vast interval of time which separates the Erian period
from the present day.
It may be proper to mention here the alleged Pulmonifera of the
genus _Palæorbis_ described by some German naturalists. These I
believe to be worm tubes of the genus _Spirorbis_, and in fact to
be nothing else than the common _S. carbonarius_ or _S. pusillus_
of the coal formation. The history of this error may be stated
thus. The eminent palæobotanists Germar, Goeppert and Geinitz have
referred the _Spirorbis_, so common in the Coal measures to the fungi,
under the name _Gyromyces_, and in this they have been followed
by other naturalists, though as long ago as 1868 I had shown that
this little organism is not only a calcareous shell, attached by
one side to vegetable matters and shells of mollusks, but that it
has the microscopic structure characteristic of modern shells of
this type.[139] More recently Van Beneden, Cænius, and Goldenberg,
perceiving that the fossil is really a calcareous shell, but
apparently unaware of the observations made in this country by myself
and Mr. Lesquereux, have held the _Spirorbis_ to be a pulmonate mollusk
allied to _Planorbis_, and have supposed that its presence on fossil
plants is confirmatory of this view, though the shells are attached
by a flattened side to these plants, and are also found attached to
shells of bivalves of the genus _Naiadites_. Mr. R. Etheridge, jun.,
of the Geological Survey of Great Britain, has summed up the evidence
as to the true nature of these probably brackish-water shells, and
has revised and added to the species, in a series of articles in the
_Geological Magazine_ of London, vol. viii.
[139] "Acadian Geology," 2nd edition, p. 205.
The erect trees of Coal Mine Point are rich in remains of Millipedes.
The first of these (_Xylobius Sigillariæ_), which was the first known
Palæozoic Myriapod, was described by me from specimens found in a
tree extracted in 1852, and this, with a number of other remains
subsequently found, was afterwards placed in the hands of Dr.
Scudder, who has recognised in the material submitted to him eight
species belonging to three genera (_Xylobius_, _Archiulus_, and
_Amynilyspes_). These animals in all probability haunted these trees
to feed on the decaying wood and other vegetable matter, and were
undoubtedly themselves the prey of the Microsaurians. Though these
were the earliest known, their discovery was followed by that of many
other species in Europe and America, and some of them as old as the
Devonian.[140]
[140] The two first-named genera from the erect trees, according to
Scudder, belong to an extinct family of Millipedes, which he names
Archiulidæ, and places with other Carboniferous genera in the order
_Archipolypoda_. The third belongs to family Euphoberidæ. Proc. R. S.
of London, 1892.
The only other remains of Air-breathers found in the erect trees
belong to Scorpions, of which some fragments remain in such a state
as to make it probable that they have been partially devoured by the
imprisoned reptiles. No remains of any aquatic animals have been found
in these trees. The Scorpions are referred by Scudder to three species
belonging to two genera.[141]
[141] _Mazonia Acadica_, and a second species of _Mazonia_, with
fragments of a third species, generally distinct. Proceedings Royal
Society of London, 1892.
In the previous paper we have considered the mode of accumulation
of Coal, and it may be useful here to note the light thrown on this
subject by the Air-breathers of the coal formation and their mode of
occurrence.
In no part of the world are the coal measures better developed, or
more fully exposed, than in the coast sections of Nova Scotia and Cape
Breton; and in these, throughout their whole thickness, no indication
has been found of any of the marine fossils of the Lower Carboniferous
Limestone. Abundant remains of fishes occur, but these may have
frequented estuaries, streams and ponds, and the greater part of them
are small ganoids which, like the modern _Lepidosteus_ and _Amia_, may
have been specially fitted by their semi-reptilian respiration, for
the impure waters of swampy districts. Bivalve mollusks also abound;
but these are all of the kinds to which I have given the generic name
_Naiadites_, and Mr. Salter those of _Anthracomya_ and _Anthracoptera_.
These shells are all distinct from any known in the marine limestones.
Their thin edentulous valves, their structure consisting of a wrinkled
epidermis, a thin layer of prismatic shell and an inner layer of
imperfectly pearly shell, all remind us of the Anodons and Unios.
A slight notch in front concurs with their mode of occurrence in
rendering it probable that, like mussels in modern estuaries, they
attached themselves to floating or sunken timber. They are thus
removed, both in structure and habit, from truly marine species; and
may have been fresh-water or brackish-water mussels closely allied to
modern Unios.
[Illustration: Carboniferous Millipedes, _Xylobius Sigillariæ_, Dawson
(_a, c_), and _Archiulus xylobioides_, Scudder (_b_).
Carboniferous Cockroach.--_Blattina Bretonensis_, Sc.
Carboniferous Scorpion.--_Anthracomartus Carbonarius_, abdominal
segments.]
The crustaceans (_Eurypterus_, _Diplostylus_, _Cyprids_), and the
worm shell (_Spirorbis_) found with them, are not necessarily marine,
though some of them belonged probably to brackish water, and they have
not yet been found in those carboniferous beds deposited in the open
sea. There is thus in the whole thickness of the middle coal measures
of Nova Scotia a remarkable absence at least of open sea animals; and
if, as is quite probable, the sea inundated at intervals the areas of
coal accumulation, the waters must have been shallow, and to a great
extent land-locked, so that brackish-water rather than marine animals
inhabited them.
On the other hand, there are in these coal measures abundant evidences
of land surfaces; and subaërial decay of vegetable matter in large
quantity is proved by the occurrence of the mineral charcoal of the
coal itself, as I have elsewhere shown.[142] The erect trees which
occur at so many levels also imply subaërial decay. A tree imbedded in
sediment and remaining under water, could not decay so as to become
hollow and deposit the remains of its wood in the state of mineral
charcoal within the hollow bark. Yet this is the case with the greater
part of the erect Sigillariæ which occur at more than twenty levels in
the Joggins section. Nor could such hollow trunks become repositories
for millipedes, snails and reptiles, if under water. On the other hand,
if, as seems necessary to explain the character of the reptiliferous
erect trees, these remained dry, or nearly so, in the interior, this
would imply not merely a soil out of water, but comparatively well
drained; as would indeed always be the case, when a flat resting on a
sandy subsoil was raised several feet above the level of the water.
Further, though the peculiar character of the roots of _Sigillariæ_
and _Calamites_ may lend some countenance to the supposition that they
could grow under water, or in water-soaked soils, this will not apply
to coniferous trees, to ferns, and other plants, which are found under
circumstances which show that they grew with the _Sigillariæ_.
[142] _Journal of Geological Survey_, vol. xv.
In the coal measures of Nova Scotia, therefore, while marine conditions
are absent, there are ample evidences of fresh-water or brackish-water
conditions, and of land surfaces, suitable for the air-breathing
animals of the period. Nor do I believe that the coal measures of Nova
Scotia were exceptional in this respect. It is true that in Great
Britain evidences of marine life do occur in the coal measures; but
not, so far as I am aware, in circumstances which justify the inference
that the coal is of marine origin. Alternations of marine and land
remains, and even mixtures of these, are frequent in modern submarine
forests. When we find, as at Fort Lawrence in Nova Scotia, a modern
forest rooted in upland soil forty feet below high-water mark,[143]
and covered with mud containing living Tellinas and Myas, we are not
justified in inferring that this forest grew in the sea. We rather
infer that subsidence has occurred. In modern salt marshes it is not
unusual to find every little runnel or pool full of marine shell
fish, while in the higher parts of the marsh land plants are growing;
and in such places the deposit formed must contain a mixture of land
plants and marine animals with salt grasses and herbage--the whole _in
situ_.[144]
[143] _Journal of Geological Society_, vol. xi.
[144] In the marshes at the mouth of Scarborough River, in Maine,
channels not more than a foot wide, and far from the sea, are full of
Mussels and Myæ; and in little pools communicating with these channels
there are often many young _Limuli_, which seem to prefer such places,
and the cast-off shells and other remains of which may become imbedded
in mud and mixed with land plants, just as in the shales of the coal
measures.
These considerations serve, I think, to explain all the apparently
anomalous associations of coal plants with marine fossils; and I do
not know any other arguments of apparent weight that can be adduced
in favour of the marine or even aquatic origin of coal, except such
as are based on misconceptions of the structure and mode of growth of
sigillaroid trees and of the stratigraphical relations of the coal
itself.[145] It is to be observed, however, that while I must maintain
the essentially terrestrial character of the ordinary coal and of
its plants, I have elsewhere admitted that cannel coals and earthy
bitumen present evidences of subaquatic deposition; and have also
abundantly illustrated the facts that the coal plants grew on swampy
flats, liable not only to river inundations, but also to subsidence and
submergence.[146] In the oscillation of these conditions it is evident
that _Sigillariæ_ and their contemporaries must often have been placed
in conditions unfavourable or fatal to them, and when their remains
are preserved to us in these conditions, we may form very incorrect
inferences as to their mode of life. Further, it is to be observed that
the conditions of submergence and silting up which were favourable to
the preservation of specimens of _Sigillariæ_ as fossils, must have
been precisely those which were destructive to them as living plants;
and on the contrary, that the conditions in which these forests may
have flourished for centuries must have been those in which there was
little chance of their remains being preserved to us, in any other
condition at least than that of coal, which reveals only to careful
microscopic examination the circumstances, whether aërial or aquatic,
under which it was formed.
[145] It is unfortunate that few writers on this subject have combined
with the knowledge of the geological features of the coal a sufficient
acquaintance with the phenomena of modern marshes and swamps, and with
the conditions necessary for the growth of plants such as those of the
coal. It would be easy to show, were this a proper place to do so, that
the "swells," "rock faults," splitting of beds, and other appearances
of coal seams quite accord with the theory of swamp accumulation; that
the plants associated with _Sigillariæ_ could not have lived with
their roots immersed in salt water; that the chemical character of
the underclays implies drainage and other conditions impossible under
the sea; that the composition and minute structure of the coal are
incompatible with the supposition that it is a deposit from water, and
especially from salt water; and that it would be more natural to invoke
wind driftage as a mode of accumulation for some of the sandstones,
than water driftage for the formation of the coal. At the same time it
is pretty certain that such beds as the cannels and earthy bitumens
which appear to consist of finely comminuted vegetable matter, without
mineral charcoal, may have been deposits of muck in shallow lakes or
lagoons.
[146] _Journal of Geol. Socy._, vols. x. and xv., and "Acadian Geology."
It is also noticeable that, in conditions such as those of the coal
formation, it would be likely that some plants would be specially
adapted to occupy newly emerged flats and places liable to inundation
and silting up. I believe that many of the Sigillariæ, and still more
eminently the _Calamites_, were suitable to such stations. There
is direct evidence that the nuts named Trigonocarpa were drifted
extensively by water over submerged flats of mud. Many _Cardiocarpa_
were winged seeds which may have drifted in the air. The Calamites
may, like modern _Equiseta_, have produced spores with elaters capable
of floating them in the wind. One of the thinner coals at the Joggins
is filled with spores or spore cases that seem to have carried
hairs on their surfaces, and may have been suited to such a mode of
dissemination. I have elsewhere proved[147] that at least some species
of _Calamites_ were, by their mode of growth, admirably fitted for
growing amid accumulating sediment, and for promoting its accumulation.
[147] "Acadian Geology," chapter on Coal Plants.
The reptiles of the coal formation are probably the oldest known to us,
and possibly, though this we cannot affirm, the highest products of
creation in this period. Supposing, for the moment, that they are the
highest animals of their time, and, what is perhaps less likely, that
those which we know are a fair average of the rest, we have the curious
fact that they are all carnivorous, and the greater part of them fitted
to find food in the water as well as on the land. The plant feeders of
the period, on the land at least, are all invertebrates, as snails,
millipedes, and perhaps insects. The air-breathing vertebrates are not
intended to consume the exuberant vegetable growth, but to check the
increase of its animal enemies. Plant life would thus seem to have had
in every way the advantage. The millipedes probably fed only on roots
and decaying substances, the snails on the more juicy and succulent
plants growing in the shadow of the woods, and the great predominance
of the family of cockroaches among carboniferous insects points to
similar conclusions as to that class. While, moreover, the vegetation
of the coal swamps was most abundant, it was not, on the whole, of a
character to lead us to suppose that it supported many animals. Our
knowledge of the flora of the coal swamps is sufficiently complete to
exclude from them any abundance of the higher phænogamous plants. We
know little, it is true, of the flora of the uplands of the period; but
when we speak of the coal-formation land, it is to the flats only that
we refer. The foliage of the plants on these flats with the exception
of that of the ferns, was harsh and meagre, and there seem to have been
no grasses or other nutritious herbaceous plants. These are wants of
themselves likely to exclude many of the higher forms of herbivorous
life. On the other hand, there was a profusion of large nut-like seeds,
which in a modern forest would probably have afforded subsistence to
squirrels and similar animals. The pith and thick soft bark of many
of the trees must at certain seasons have contained much nutritive
matter, while there was certainly sufficient material for all those
insects whose larvæ feed on living and dead timber, as well as for
the creatures that in turn prey on them. It is remarkable that there
seem to have been no vertebrate animals fitted to avail themselves of
these vast stores of food. The question: "What may have fed on all
this vegetation?" was never absent from my mind in all my explorations
of the Nova Scotia coal sections; but no trace of any creature other
than those already mentioned has ever rewarded my search. In Nova
Scotia it would seem that a few snails, gally-worms, and insects
were the sole links of connection between the plant creation and
air-breathing vertebrates. Is this due to the paucity of the fauna, or
the imperfection of the record? The fact that a few erect stumps have
revealed nearly all the air-breathers yet found, argues strongly for
the latter cause; but there are some facts bearing on the other side.
A gally-worm, if, like its modern relatives, hiding in crevices of
wood in forests, was one of the least likely animals to be found in
aqueous deposits. The erect trees gave it its almost sole chance of
preservation. _Pupa vetusta_ is a small species, and its shell very
thin and fragile, while it probably lived among thick vegetation.
Further, the measures 2,000 feet thick, separating the lowest and
highest beds in which it occurs, include twenty-one coal seams, having
an aggregate thickness of about twenty feet, three beds of bituminous
limestone of animal origin, and perhaps twenty beds holding _Stigmaria_
_in situ_, or _erect_ _Sigillariæ_ and _Calamites_. The lapse of time
implied by this succession of beds, many of them necessarily of very
slow deposition, must be very great, though it would be mere guess work
to attempt to resolve it into years. Yet long though this interval must
have been, _Pupa vetusta_ lasted without one iota of change through
it all; and, more remarkable still, was not accompanied by more than
two other species of its family. Where so many specimens occur, and in
situations so diverse, without any additional species, the inference
is strong that no other of similar habits existed. If in any of those
subtropical islands, whose climate and productions somewhat resemble
those of the coal period, after searching in and about decaying trees,
and also on the bars upon which rivers and lakes drifted their burdens
of shells, we should find only three species, but one of these in very
great numbers, we would surely conclude that other species, if present,
were very rare.
Again, footprints referable to _Dendrerpeton_, or similar animals,
occur in the lower Carboniferous beds below the marine limestones, in
the middle coal measures, and in the upper coal formation, separated
by a thickness of beds which may be estimated at 15,000 feet, and
certainly representing a vast lapse of time. Did we know the creature
by these impressions alone, we might infer its continued existence for
all this great length of time; but when we also find its bones in the
principal repositories of reptile remains, and in company with the
other creatures found with it, we satisfy ourselves that of them all it
was the most likely to have left its trail in the mud flats. We thus
have reason to conclude that it existed alone during this period, in so
far as its especial kind of habitat was concerned; though there lived
with it other reptiles, some of which, haunting principally the woods,
and others the water, were less likely to leave impressions of their
footprints. These may be but slight indications of truth, but they
convey strong impressions of the persistence of species, and also of
the paucity of species belonging to these tribes at the time.
If we could affirm that the Air-breathers of the coal period were
really the first species of their families, they might acquire
additional interest by their bearing on this question of origin of
species. We cannot affirm this; but it may be a harmless and not
uninstructive play of fancy to suppose for a moment that they actually
are so, and to inquire on this supposition as to the mode of their
introduction. Looking at them from this point of view, we shall first
be struck with the fact that they belong to all of the three great
leading types of animals which include our modern Air-breathers the
Vertebrates, the Arthropods, and the Mollusks. We have besides to
consider in this connection that the breathing organs of an insect are
air tubes opening laterally (tracheæ), those of a land snail merely a
modification of the chamber which in marine species holds the gills,
while those of the reptiles represent the air bladder of the fishes.
Thus, in the three groups the breathing organs are quite distinct in
their nature and affinities. This at once excludes the supposition that
they can all have been derived from each other within the limits of the
coal period. No transmutationist can have the hardihood to assert the
convertibility, by any direct method, of a snail into a millipede or
an insect, or of either into a reptile. The plan of structure in these
creatures is not only different, but contrasted in its most essential
features. It would be far more natural to suppose that these animals
sprang from aquatic species of their respective types. We should then
seek for the ancestors of the snail in aquatic Gasteropods, for those
of the millipede in worms or Crustaceans, and for those of the reptiles
in the fishes of the period. It would be easy to build up an imaginary
series of stages, on the principle of natural selection, whereby these
results might be effected; but the hypothesis would be destitute of
any support from fact, and would be beset by more difficulties than it
removes. Why should the result of the transformation of water-snails
breathing by gills be a _Pupa ?_ Would it not much more likely be an
_Auricula_ or a _Limnea ?_ It will not solve this difficulty to say
that the intermediate forms became extinct, and so are lost. On the
contrary, they exist to this day, though they were not, in so far
as we know, introduced so early. But negative evidence must not be
relied on; the record is very imperfect, and such creatures may have
existed, though unknown to us. It may be answered that they could not
have existed in any considerable numbers, else some of their shells
would have appeared in the coal-formation beds, so rich in crustaceans
and bivalve mollusks. Further, the little Pupa remained unchanged
during a very long time, and shows no tendency to resolve itself into
anything higher, or to descend to anything lower, while in the lowest
bed in which it occurs it is associated with a round snail of quite
different type. Here, if anywhere, in what appears to be the first
introduction of air-breathing invertebrates, we should be able to find
the evidences of transition from the gills of the Prosobranchiate
and the Crustacean to the air sac of the Pulmonate and the tracheæ of
the millipede. It is also to be observed that many other structural
changes are involved, the aggregate of which makes a Pulmonate or a
millipede different in every particular from its nearest allies among
gill-bearing Gasteropods or Crustaceans.
It may be said, however, that the links of connection between the coal
reptiles and fishes are better established. All the known coal reptiles
have leanings to the fishes in certain characters; and in some, as
in _Archegosaurus_, these are very close. Still the interval to be
bridged over is wide, and the differences are by no means those which
we should expect. Were the problem given to convert a ganoid fish into
an _Archegosaurus_ or _Dendrerpeton_, we should be disposed to retain
unchanged such characters as would be suited to the new habits of the
creature, and to change only those directly related to the objects
in view. We should probably give little attention to differences in
the arrangement of skull bones, in the parts of the vertebræ, in the
external clothing, in the microscopic structure of the bone, and other
peculiarities for serving similar purposes by organs on a different
plan, which are so conspicuous so soon as we pass from the fish to the
Batrachian. It is not, in short, an improvement of the organs of the
fish that we witness so much as the introduction of new organs.[148]
The foot of the batrachian bears, perhaps, as close a relation to the
fin of the fish as the screw of one steamship to the paddle wheel
of another, or as the latter to a carriage wheel; and can be just
as rationally supposed to be not a new instrument, but the old one
changed. In this connection even a footprint in the sand startles us as
much as that of Friday did Robinson Crusoe. We see five fingers and
toes, and ask how this numerical arrangement started at once from fin
rays of fishes all over the world; and how it has continued unchanged
till now, when it forms the basis of our decimal arithmetic.
[148] An ingenious attempt by Prof. Cope, to deduce the batrachian foot
from the fins of certain carboniferous fishes, will be found in the
_Proceedings of the Philos. Academy of Philadelphia_ for the present
year.
Again, our reptiles of the coal do not constitute a continuous series,
and belong to a great number of distinct genera and families, nor
is it possible that they can all, except at widely different times,
have originated from the same source. It either happened, for some
unknown reason, that many kinds of fishes put on the reptilian guise
in the same period, or else the vast lapse of ages required for the
production of a reptile from a fish must be indefinitely increased for
the production of many dissimilar reptiles from each other; or, on the
other hand, we must suppose that the limit between the fish and reptile
being once overpassed, a facility for comparatively rapid changes
became the property of the latter. Either supposition would, I think,
contradict such facts bearing on the subject as are known to us.
We commenced with supposing that the reptiles of the Coal might
possibly be the first of their family, but it is evident from the
above considerations, that on the doctrine of natural selection, the
number and variety of reptiles in this period would imply that their
predecessors in this form must have existed from a time as early as
any in which even fishes are known to exist; so that if we adopt any
hypothesis of derivation, it would probably be necessary to have
recourse to that which supposes at particular periods a sudden and
as yet unaccountable transmutation of one form into another; a view
which, in its remoteness from anything included under ordinary natural
laws, does not materially differ from that currently received idea of
creative intervention, with which, in so far as our coal reptiles can
inform us, we are for the present satisfied.
There is one other point which strikes the naturalist in considering
these animals, and which has a certain bearing on such hypothesis.
It is the combination of various grades of reptilian types in these
ancient creatures. It has been well remarked by Hugh Miller, and more
fully by Agassiz, that this is characteristic of the first appearance
of new groups of animals. Now selection, as it acts in the hands of the
breeder, tends to specialization; and natural selection, if there is
such a thing, is supposed to tend in the same direction. But when some
distinctly new form is to be introduced, an opposite tendency seems to
prevail, a sort of aggregation in one species of characters afterward
to be separated and manifested in distinct groups of creatures. The
introduction of such new types also tends to degrade and deprive of
their higher properties previously existing groups of lower rank. It is
easy to perceive in all this, law and order, in that higher sense in
which these terms express the will and plan of the Supreme Mind, but
not in that lower sense in which they represent the insensate operation
of blind natural forces.
References:--"Air-breathers of the Coal Period." Montreal, 1886.
Papers on Reptiles, etc., in South Joggins Coal Field, _Journal
of Geological Society of London_, vols. ix. x. xi. xvi. Remains
of Animals in Erect Trees in the Coal Formation of Nova Scotia,
_Trans. Royal Society_, 1881. "Acadian Geology," fourth edition,
1891. Revision of Land Snails of the Palæozoic Era, _Am. Journal of
Science_, vol. xx., 1880. Supplementary Report to Royal Society of
London, Proceedings, 1892. Notice of additional Reptilian Remains,
_Geological Magazine of London_, 1891.
_MARKINGS, FOOTPRINTS AND FUCOIDS._
DEDICATED TO THE MEMORY OF THE LATE
DR. J. J. BIGSBY, F.R.S.,
OF LONDON,
The painstaking and accurate Author
of the Thesaurus Siluricus and Devonico-Carboniferous,
a warm and kind Friend and Christian Gentleman
and one of the
Pioneers of Canadian Geology.
Reminiscences of Lyell's Work--Tidal Flats of the Bay of Fundy--Rill
Marks and Shrinkage Cracks--Worm Trails and Burrows--The Paces of
Limulus--Fucoids Versus Trails--Footprints of Vertebrates
[Illustration: Track of Limulus.--Modern, Orchard Beach. Showing its
resemblance to the _Protichnites_ of the Cambrian. (Page 320.)]