<h2><span class="pagenum"><SPAN name="P26"></SPAN></span><SPAN name="chapVI"></SPAN>VI<br/> THE AGE OF REPTILES</h2>
<p>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.</p>
<p>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.</p>
<p>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. <span class="pagenum"><SPAN name="P27"></SPAN></span>This new land life
needed only the opportunity of favourable conditions to flourish and
prevail.</p>
<div class="fig"> <SPAN name="img-27"></SPAN> <ANTIMG src="images/img-27.jpg" alt="A FOSSIL ICHTHYOSAURUS, A MESOZOIC FISH-LIZARD" width-obs="674" height-obs="368" /> <p class="caption">
A FOSSIL ICHTHYOSAURUS, A MESOZOIC FISH-LIZARD
<br/>
<small>Found in the Lower Lias in Somersetshire
<br/>
<i>Nat. Hist. Mus.</i></small></p>
</div>
<p>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.</p>
<p>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),
<span class="pagenum"><SPAN name="P28"></SPAN></span>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.</p>
<div class="fig"> <SPAN name="img-28"></SPAN> <ANTIMG src="images/img-28.jpg" alt="A PTERODACTYL" width-obs="661" height-obs="265" /> <p class="caption">
A PTERODACTYL
<br/>
<small><i>Nat. Hist. Mus.</i></small></p>
</div>
<p>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 <i>Diplodocus Carnegii</i> 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.
<span class="pagenum"><SPAN name="P29"></SPAN></span></p>
<div class="fig"> <SPAN name="img-29"></SPAN> <ANTIMG src="images/img-29.jpg" alt="A BIG SWAMP-INHABITING DINOSAUR, THE DIPLODOCUS, OVER EIGHTY FEET FROM SNOUT TO TAIL-TIP" width-obs="665" height-obs="445" /> <p class="caption">
A BIG SWAMP-INHABITING DINOSAUR, THE DIPLODOCUS, OVER EIGHTY FEET
FROM SNOUT TO TAIL-TIP
<br/>
<small><i>Nat. Hist. Mus.</i></small></p>
</div>
<p>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.</p>
<p>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 <span class="pagenum"><SPAN name="P30"></SPAN></span>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.</p>
<p>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.</p>
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