A SHORT HISTORY OF THE WORLD
BY
H. G. WELLS
6.THE AGE OF REPTILES
The abundant life of the Carboniferous period was succeeded by a vast cycle of dry and bitter ages. They are represented in the Record of the Rocks by thick deposits of sandstones and the like, in which fossils are comparatively few. The temperature of the world fluctuated widely, and there were long periods of glacial cold. Over great areas the former profusion of swamp vegetation ceased, and, overlaid by these newer deposits, it began that process of compression and mineralization that gave the world most of the coal deposits of to-day. But it is during periods of change that life undergoes its most rapid modifications, and under hardship that it learns its hardest lessons. As conditions revert towards warmth and moisture again we find a new series of animal and plant forms established, We find in the record the remains of vertebrated animals that laid eggs which, instead of hatching out tadpoles which needed to live for a time in water, carried on their development before hatching to a stage so nearly like the adult form that the young could live in air from the first moment of independent existence. Gills had been cut out altogether, and the gill slits only appeared as an embryonic phase.
These new creatures without a tadpole stage were the Reptiles.
Concurrently there had been a development of seed-bearing trees, which
could spread their seed, independently of swamp or lakes. There were
now palmlike cycads and many tropical conifers, though as yet there
were no flowering plants and no grasses. There was a great number of
ferns. And there was now also an increased variety of insects. There
were beetles, though bees and butterflies had yet to come. But all the
fundamental forms of a new real land fauna and flora had been laid down
during these vast ages of severity. This new land life needed only the
opportunity of favourable conditions to flourish and prevail.
Age by age and with abundant fluctuations that mitigation came. The
still incalculable movements of the earth’s crust, the changes in its
orbit, the increase and diminution of the mutual inclination of orbit
and pole, worked together to produce a great spell of widely diffused
warm conditions. The period lasted altogether, it is now supposed,
upwards of two hundred million years. It is called the Mesozoic
period, to distinguish it from the altogether vaster Palæozoic and
Azoic periods (together fourteen hundred millions) that preceded it,
and from the Cainozoic or new life period that intervened between its
close and the present time, and it is also called the Age of Reptiles
because of the astonishing predominance and variety of this form of
life. It came to an end some eighty million years ago.
In the world to-day the genera of Reptiles are comparatively few and
their distribution is very limited. They are more various, it is true,
than are the few surviving members of the order of the amphibia which
once in the Carboniferous period ruled the world. We still have the
snakes, the turtles and tortoises (the Chelonia), the alligators and
crocodiles, and the lizards. Without exception they are creatures
requiring warmth all the year round; they cannot stand exposure to
cold, and it is probable that all the reptilian beings of the Mesozoic
suffered under the same limitation. It was a hothouse fauna, living
amidst a hothouse flora. It endured no frosts. But the world had at
least attained a real dry land fauna and flora as distinguished from
the mud and swamp fauna and flora of the previous heyday of life upon earth.
All the sorts of reptile we know now were much more abundantly
represented then, great turtles and tortoises, big crocodiles and many
lizards and snakes, but in addition there was a number of series of
wonderful creatures that have now vanished altogether from the earth.
There was a vast variety of beings called the Dinosaurs. Vegetation was
now spreading over the lower levels of the world, reeds, brakes of fern
and the like; and browsing upon this abundance came a multitude of
herbivorous reptiles, which increased in size as the Mesozoic period
rose to its climax. Some of these beasts exceeded in size any other
land animals that have ever lived; they were as large as whales. The
_Diplodocus Carnegii_ for example measured eighty-four feet from snout
to tail; the Gigantosaurus was even greater; it measured a hundred
feet. Living upon these monsters was a swarm of carnivorous Dinosaurs
of a corresponding size. One of these, the Tyrannosaurus, is figured
and described in many books as the last word in reptilian
frightfulness.
While these great creatures pastured and pursued amidst the fronds and
evergreens of the Mesozoic jungles, another now vanished tribe of
reptiles, with a bat-like development of the fore limbs, pursued
insects and one another, first leapt and parachuted and presently flew
amidst the fronds and branches of the forest trees. These were the
Pterodactyls. These were the first flying creatures with backbones;
they mark a new achievement in the growing powers of vertebrated life.
Moreover some of the reptiles were returning to the sea waters. Three
groups of big swimming beings had invaded the sea from which their
ancestors had come: the Mososaurs, the Plesiosaurs, and Ichthyosaurs.
Some of these again approached the proportions of our present whales.
The Ichthyosaurs seem to have been quite seagoing creatures, but the
Plesiosaurs were a type of animal that has no cognate form to-day. The
body was stout and big with paddles, adapted either for swimming or
crawling through marshes, or along the bottom of shallow waters. The
comparatively small head was poised on a vast snake of neck, altogether
outdoing the neck of the swan. Either the Plesiosaur swam and searched
for food under the water and fed as the swan will do, or it lurked
under water and snatched at passing fish or beast.
Such was the predominant land life throughout the Mesozoic age. It was
by our human standards an advance upon anything that had preceded it.
It had produced land animals greater in size, range, power and
activity, more “vital” as people say, than anything the world had seen
before. In the seas there had been no such advance but a great
proliferation of new forms of life. An enormous variety of squid-like
creatures with chambered shells, for the most part coiled, had appeared
in the shallow seas, the Ammonites. They had had predecessors in the
Palæozoic seas, but now was their age of glory. To-day they have left
no survivors at all; their nearest relation is the pearly Nautilus, an
inhabitant of tropical waters. And a new and more prolific type of
fish with lighter, finer scales than the plate-like and tooth-like
coverings that had hitherto prevailed, became and has since remained
predominant in the seas and rivers.