THE AGE OF REPTILES
We have already said that in the many hundreds of thousands of
years which went by during Carboniferous times the sea sometimes
advanced and sometimes receded, and nothing shows this better than
the great thickness of the deposits in which the coal lies in
seams. In America, as in Europe, Asia, Africa, Australia, and New
Zealand, South and Central America, the Carboniferous system is
found. In Arkansas, in North America, the coal measures attain the
remarkable thickness of 18,000 feet; in the Wasatch Mountains the
Carboniferous strata have been estimated to be 13,000 feet thick,
and in silver-bearing Nevada 10,000 feet. The formations of the
Western European coal measures, like those of Eastern North America,
consist principally of shales and clays, with smaller amounts of
sandstone and limestone. They attain great thickness, and, including
5500 feet of the Millstone Grit, are 13,500 feet thick in Lancashire
and several thousand feet thick in many parts of Great Britain and
Ireland. The extraordinary thicknesses show that near our islands
must have been a very extensive and lofty area of land. In Germany
the same strata, thickly seamed with coal, are 10,000 feet thick.
There must also have been considerable volcanic or earthquake
action as we know, because in Germany, near the Hartz Mountains and
elsewhere, there are many igneous rocks thrust into the strata,
and also because in Belgium and in France the coal strata are very
much twisted and contorted. The same or similar beds are found in
Siberia, in Japan, and in China, where the coal beds are said to be
thicker than anywhere else in the world. The Carboniferous system
is also found in Africa, in the north, south-east, and south of the
continent; and in Australia and New Zealand Carboniferous strata to
the thickness of 10,000 feet are indicated.
At the close of this period the changes ever taking place transformed
the conditions of life in a way the reverse of that which we have
hitherto been examining. So far each age has shown an increase
of life on the age preceding it. But when the great outburst of
carboniferous activity began to wane it was followed by a lessening
of the wave of life. As we said in the last chapter, there lie on the
top of the coal-bearing strata beds to which the older geologists
gave the name of New Red Sandstone. But in 1841 the New Red Sandstone
was divided into two distinct geological formations. To the lower
and older part Murchison gave in 1841 the name of Permian (from
_Perm_ or _Permia_, an ancient kingdom in Russia, where red sandy
rocks of this age form nearly all the surface), but in Germany it
is more frequently called the Dyas (from Lat. _duo_, two), because
in that country it is composed of _two_ well-marked divisions--red
sandstones below and magnesian limestones above. Thus there are two
types of this Permian formation: the Permian type proper--a mixed
series of red sandstones, marls, shales, and limestones, with some
thin beds of coal, as found in Russia; and the Dyassic type, as seen
in Germany.
We do not know what brought about the change: though we do know
that during it there was great volcanic activity over Europe and
that the waning forests of vegetation and the steaming swamps gave
place to desert plains. Vegetation sank lower and lower. The forests
disappeared or dwelt only in clusters. The soft sappy trees gave
place to hardy pines which clung to the plains and the mountains, and
other sterner types began to appear, allied to the spruces, yews,
and ginkgo. The ginkgo tree is one of the oldest of the tree type
which now has a living representative. Any reader interested enough
in the matter to walk along Royal Hospital Road, Chelsea, will find a
ginkgo tree just outside the Old Physic Garden; and of course a good
many other examples are preserved in botanic gardens. The cycads,
offshoots of the ferns, through the strange group of trees known as
the cycado-filices, spread through the woods.
The trilobites, to turn to animal life, all but disappeared,
though one elegant example remained; the corals were changing; and
the lamp-shells were dropping out. There were a few new species
of fishes, but none of any great strength or capacity, and all
preserving still the tail which is part of the backbone. There was an
all-round impoverishment of life--so great, indeed, that the early
geologists used to believe that a complete destruction of all life
followed this, the closing stage of the Palæozoic era, and that a
re-creation followed. They would have been confirmed in this belief
had they but known that intense cold and glaciation were setting
in where the tropics were situated and that the dryness of vast
deserts was sweeping away life elsewhere. But we now know that life
was not entirely lost; that many species survived, and that others,
altering to suit altering conditions, became stronger in the process.
Nevertheless, life was greatly impoverished. A census made a few
years ago gave the known animal species of the Carboniferous period
as 10,000, while those of the Permian period were only 300, or three
per cent. Possibly the percentage was larger than that, but still it
was small.
But if the Permian was poor in life it was very interesting. The
amphibians had been growing in strength during the later stages of
the Carboniferous age, and may possibly have been more numerous then
than at any other time, for the vast swamps were very favourable for
them. They diminished in the Permian, though the Permian amphibians
showed some advances, and began to assume a likeness to reptiles.
Perhaps the reptiles may have first appeared in the Carboniferous,
but they declared themselves in the Permian age. Two great branches
of reptiles seem already to have defined themselves; perhaps they
had never formed a common group as reptiles, but had separated while
still amphibians. The one bore resemblance to, and were perhaps the
forerunners of, the great hosts of lizards, crocodiles, dinosaurs,
ichthyosaurs, and flying saurians, which are the most pronounced
of the reptiles, and of which we shall have a great deal to say
presently. The other group were perhaps the ancestors of the turtles
and plesiosaurs which appeared later, and possibly led the way to
the mammals. This rapid and diverse spreading out of the reptiles
in a period when life as a whole was at a low ebb is not a little
remarkable. These creatures seem to show the arrival of a more
pronounced form of _air-breathing_ animal; and that may have been the
consequence of the presence of more oxygen in the earth's atmosphere.
Of the Permian amphibians, one of the most interesting was like the
Sphenodon, which still creeps about the northern islands of New
Zealand. The most striking of the reptiles was the _Naosaurus_, a
beast-like creature with a high back of spines webbed together like a
solid porcupine. It was from three to ten feet in length.
All these changes were brought about by the general withdrawal of
the sea, both in the North American continent and in Europe. In both
continents there are beds which accumulated fresh water; in both beds
which were laid down in salt lakes or inland seas; and in both beds
which were laid down on the floor of seas washing the continents.
Great areas seem to have been sometimes dry and sometimes submerged;
other and greater areas, bordered by ice and sometimes swept by icy
blasts, or subject to burning sun in summer, were deserts such as
we are aware of now in Asia or North Africa or mid-Australia, but
much larger in extent than any of these. It was in conditions such
as these that the ancient or Palæozoic rocks came to an end and the
Mesozoic or Middle Period began.
The Middle period of strata and of the life which those strata have
preserved has usually been separated from the older rocks because,
owing to the great period of arid desert conditions, the character of
life changed a great deal; but fuller knowledge shows that the links
were still there, and that ceaseless adaptation of animals to their
surroundings was ceaselessly going on. We need not follow closely
all the changes and relationships, and only much greater knowledge
than geologists yet possess will enable them to trace all the
alterations of the land and sea. But we may trace the alterations in
the appearance of the continents in broad outline. Nearly the whole
extent of the British Isles was now above the sea, and was enjoying a
climate perhaps as cold as present-day Iceland. To the south and east
of Scotland was a great shallow inland lake, while north of Great
Britain a huge plain stretched across Europe. To the south of the
lake was a belt of land, and farther south still the sea had invaded
Italy and reached to Southern Germany, and in this sea was being
laid down the limestone which in later eras was to be elevated into
the mountains of the Apennines, the Alps, and the Pyrenees. North
Africa was under water, but farther south the uplifted lands were
joining hands with India. Sea swept part of Asia, but North America
was larger and broader than it is now, her western coast stretching
farther out into the ocean.
In this period, which is called the Triassic (the name given to it
by the German geologist Bronn because of the three distinct beds
he found in it, though the middle of these, a shelly limestone,
does not exist in Great Britain), there was a wide development of
large reptiles and amphibians. We cannot enumerate them all, for
not one chapter nor one volume would suffice to deal adequately
with the reptiles of the Trias formations and of the Jurassic rocks
which followed them, and of the Permian which preceded them. But
we may speak of some of them. One of the most striking was the
_Pareiasaurus_, which has been found in the Jurassic sandstones and
limestones of South Africa, of Russia, of India and Scotland, and of
middle England. The skeleton of the Pareiasaurus looks like that of a
gigantic pug dog eight feet long; but it was a comparatively harmless
animal, the teeth of which show that it largely fed on vegetable food.
In Sir E. Ray Lankester's lectures on "Extinct Animals" he described
the finding of a great many of these fossil reptiles by Professor
Amalitzky on the banks of the River Dwina, near Archangel. There is a
cliff of Permian strata on the banks of the Dwina, and in this cliff
there is a peculiar pocket or accumulation of sandy matter with large
hard nodules embedded in it. These nodules are removed and broken up
for mending the roads. The pocket seems to be in a fissure and of
Triassic age, later, that is to say, than the Permian rocks on either
side of it. However that may be, the nodules are usually removed
for road-mending, and four or five years ago Professor Amalitzky on
visiting the spot was astounded and delighted to find that when
broken each nodule was seen to contain the skeleton or skull of
a great reptile. The Russian geologist determined to make a most
thorough investigation of this wonderful deposit, and for years spent
several thousand pounds in having the nodules dug out by the peasants
after the year's farming work was over, and in removing them to the
University of Warsaw, where with the finest instruments and greatest
care the nodules are opened, and each bone removed in fragments is
put together from its more or less broken parts, and firmly cemented
and set up in its natural position as a complete skeleton.
These Pareiasaurs reconstructed by Professor Amalitzky were about as
big as well-grown cattle, but not so high on the legs. Living at the
same time, and its skeleton now found near them, was an enormous and
truly terrible flesh-eating animal, with a skull two feet long and
enormous tiger-like teeth. This creature was named Inostransevia.
No doubt the vegetarian herds of Pareiasaurus, whose small peg-like
teeth indicate their harmlessness, were preyed on by the terrible
Inostransevia, as were their brethren in South Africa devoured by
other carnivorous reptiles of that remote Triassic age. So we see the
co-existence of blood-sucker and victim--of the destructive oppressor
and the helpless oppressed--forced on our attention in these two
localities, Russia and South Africa, in days long before man was.
Other land forms were grotesque and curious in shape, the Chelonians
for example, big birds and crocodiles rolled into one, and clothed
in lizard-like skin--queer pear-shaped brutes with huge hind limbs,
short fore limbs, narrow chests, and pigmy skulls.
Both branches of the reptilian horde, those representing the saurians
and those which were the forerunners of the mammals, sent delegations
to the sea before the close of the Triassic period. The Ichthyosaurs
represented the more pronounced reptilian line; the Plesiosaurs were
the representatives of the coming mammals. It is not difficult to
find good reason for this movement to the sea. Besides the inevitable
tendency of every masterful race to invade all accessible realms,
the renewed extension of the sea that set in during the Triassic
period and became pronounced before its close, especially invited
this, for the shallow waters creeping out upon the land with their
now prolific life set tempting morsels before the voracious reptiles,
on the one hand, while on the other, the reduction of the land area
and the restriction of their feeding-grounds, intensified by the
multiplication of the reptiles themselves, forced a resort to the
sea. One of the reptiles of this period, the _Lariosaurus_, shows by
its development how the change affected the reptiles. In the earlier
stages of the Trias it resembled a rather swollen alligator with four
limbs symmetrically situated and used for crawling. In the later
forms of these reptiles the limbs were modified with paddles, and all
power to move about on land was lost.