CHAPTER V.
THE COLD-BLOODED AIR-BREATHERS OF THE GLOBE IN TIMES BOTH PAST AND PRESENT.
And now the transformation is complete, for when we pass on to the next division of backboned animals, the “Reptiles,” we hear nothing more of gills, nor air taken from the water, nor fins, nor fishes’ tails. From this time onward all the animals we shall study live with their heads in the air, even if their bodies may be in the water; they swim with their legs or, as in the case of the snakes, with their wriggling bodies, and they lay their eggs on the land where their young begin life at once as air-breathers.
Yet they can often remain for a long time both under water and under ground, for they are still cold-blooded animals, breathing very slowly, and easily falling into a state of torpor when the air around them is cold and chill. They are but the first step, as it were, to active land-animals; yet they have played a great part in the world, and when we know their history we shall be surprised to find how much Life has been able to make of her cold-blooded children.
To learn how this has been, however, we must travel away from home and our own surroundings. The tiny brown lizard which runs over our heaths, while its legless relation, the slowworm, burrows in the ground,—the few snakes which glide through the grass of our meadows, and the stray turtles thrown at rare intervals on our shores,—tell us very little about true reptile life. It is to Africa, India, South America, and other warm countries, that we must go to find the formidable crocodiles, huge tortoises, large monitor-lizards, and dangerous boa-constrictors, cobras, and rattle-snakes. And even then, strong and powerful as some of these creatures are, they do not tell us half the history of the cold-blooded air-breathers. For the day of reptile greatness, like that of the sharks and enamel-scaled fish, was long long ago.
Now that we know how frogs pass from water-breathing to air-breathing, and how axolotls, accustomed to live all their life in the water, can lose their gills and become land-animals, we can form an idea how in those ancient days, while still the huge-plated newts were wandering in the marshes, some creatures which had lost their gills would take to the land, and their young ones starting at once as air-breathers, as the black salamanders do now (see [p. 80]), would in time lose all traces of the double or amphibian life, and become true air-breathing reptiles.
At any rate, there we find them appearing soon after the coal-forest period passed away, at first few and far between, in company with the large amphibians, but spreading more and more as the ages passed on, till they in their turn became monarchs of the globe. Already, when the coal-forests had but just passed away, a lizard,[65] in some points like the monitors that now wander on the banks of the Nile, was living among his humbler neighbours; and from that time onwards we find more and more reptiles, till just before the time when our white chalk was being formed by the tiny slime-animals at the bottom of the sea, we should have seen strange sights if we could have been upon the globe. For the great eft was no longer
“... lord and master of earth.”
All over the world, and even in our own little England, which was then part of a great continent, cold-blooded reptiles of all sizes, from lizards a few inches long to monsters measuring fifty or sixty feet from head to tail, swarmed upon the land, in the water, and in the air. There were among them a few kinds something like our tortoises, lizards, and crocodiles; but the greater number were forms which have quite died out since birds and beasts have spread over the earth, and a wonderful and powerful set they were.
Some were vegetable-feeders, which browsed upon the trees or fed upon the water-weeds, as our elephants and giraffes, our hippopotamuses and sea-cows do now. Others were ferocious animal-eaters, and their large pointed teeth made havoc among their reptile companions, as lions and tigers do among beasts. Some swam in the water devouring the fish, while others, like birds or bats, soared in the air.
In the open ocean were the sea-lizards, some called Fish-Lizards,[66] like huge porpoises thirty feet long, but really cold-blooded reptiles, with paddles for legs, and long flattened tails for swimming. Woe to the heavily-enamel-scaled fish when these monsters came along, their pointed teeth hanging in their widely-gaping mouths as they raised their huge heads, with large open eyes, out of the water! Then among these were others with long swan-like necks and small heads,[67] which would strike at the fish below them in the water, while other slender, long-bodied monsters,[68] measuring more than seventy feet from tip to tail, flapped along the sea-shore with their four large paddles, or swam out to sea like veritable sea-serpents, devouring all that came in their way. These were all water-reptiles, while there were also many smaller land-lizards playing about upon the shore, and among the trees and bushes. But the strangest of all were perhaps the “Flying reptiles”[69] of all sizes, from one as small as a sparrow to one which measured twenty-five feet from tip to tip of its wings. These reptiles did not fly like birds, for they had no feathers, but only a broad membrane, stretching from the fifth finger of their front claw to their body, and with this they must have flown much as bats do now, while some of them were armed not only with claws, but also with hooked beaks and sharp teeth, with which they could tear their prey.