The Outline of History - H. G. Wells (most recommended books txt) 📗

a time life on the earth seems to have undergone a period of world-wide bleakness.

 

We cannot discuss fully here the changes that have gone on and are going on in the climate of the earth. A great variety of causes, astronomical movements, changes in the sun and changes upon and within the earth, combine to produce a ceaseless fluctuation of the conditions under which life exists. As these conditions change, life, too, must change or perish.

 

When the story resumes again after this arrest at the end of the Palaeozoic period we find life entering upon a fresh phase of richness and expansion. Vegetation has made great advances in the art of living out of water. While the Palaeozoic plants of the coal measures probably grew with swamp water flowing over their roots, the Mesozoic flora from its very outset included palm-like cycads and low-grown conifers that were distinctly land plants growing on soil above the water level.

 

The lower levels of the Mesozoic land were no doubt covered by great fern brakes and shrubby bush and a kind of jungle growth of trees. But there existed as yet no grass, no small flowering plants, no turf nor greensward. Probably the Mesozoic was not an age of very brightly coloured vegetation. It must have had a flora green in the wet season and brown and. purple in the dry. There were no gay flowers, no bright autumn tints before the fall of the leaf, because there was as yet no fall of the leaf. And beyond the lower levels the world was still barren, still unclothed, still exposed without any mitigation to the wear and tear of the wind and rain.

 

When one speaks of conifers in the Mesozoic the reader must not think of the pines and firs that clothe the high mountain slopes of our time. He must think of low-growing evergreens. The mountains were still as bare and lifeless as ever. The only colour effects among the mountains were the colour effects of naked rock, such colours as make the landscape of Colorado so marvellous to-day.

 

Amidst this spreading vegetation of the lower plains the reptiles were increasing mightily in multitude and variety. They were now in many cases absolutely land animals. There are numerous anatomical points of distinction between a reptile and an amphibian; they held good between such reptiles and amphibians as prevailed in the carboniferous time of the Upper Palaeozoic; but the fundamental difference between reptiles and amphibia which matters in this history is that the amphibian must go back to the water to lay its eggs, and that in the early stages of its life it must live in and under water. The reptile, on the other hand, has cut out all the tadpole stages from its life cycle, or, to be more exact, its tadpole stages are got through before the young leave the egg case. The reptile has come out of the water altogether. Some had gone back to it again, just as the hippopotamus and. the otter among mammals have gone back, but that is a further extension of the story to which we cannot give much attention in this Outline.

 

[Fig 0027 Some Mesozoic Reptiles]

 

[Fig 0027]

 

In the Palaeozoic period, as we have said, life had not spread beyond the swampy river valleys and the borders of sea lagoons and the like; but in the Mesozoic, life was growing ever more accustomed to the thinner medium of the air, was sweeping boldly up over the plains and towards the hill-sides. It is well for the student of human history and the human future to note that. If a disembodied intelligence with no knowledge of the future had come to earth and studied life during the early Paloeozoic age, he might very reasonably have concluded that life was absolutely confined to the water, and that it could never spread over the land. It found a way. In the Later Paloeozoic Period that visitant might have been equally sure that life could not go beyond the edge of a swamp. The Mesozoic Period would still have found him setting bounds to life far more limited than the bounds that are set to-day. And so to-day, though we mark how life and, man are still limited to five miles of air and a depth of perhaps a mile or so of sea, we must not conclude from that present limitation that life, through man, may not presently spread out and up and down to a range of living as yet inconceivable.

 

The earliest known reptiles were beasts with great bellies and not very powerful legs, very like their kindred amphibia, wallowing as the crocodile wallows to this day; but, in the Mesozoic they soon began to stand up and go stoutly on all fours, and several great sections of them began to balance themselves on tail and hind-legs, rather as the kangaroos do now, in order to release the fore limbs for grasping food. The bones of one notable division of reptiles which retained a quadrupedal habit, a division of which many remains have been found in South African and Russian Early Mesozoic deposits, display a number of characters which approach those of the mammalian skeleton, and because of this resemblance to the mammals (beasts) this division is called the Theriomorpha (beastlike). Another division was the crocodile branch, and, another developed towards the tortoises and turtles. The Plesiosaurs and lchthyosaurs were two groups which have left no living representatives; they were huge reptiles returning to a whale-like life in the sea. Pliosaurus, one of the largest plesiosaurs, measured thirty feet from snout to tail tip"of which half was neck. The Mosasaurs were a third group of great porpoise-like marine lizards. But the largest and most diversified group of these Mesozoic reptiles was the group we have spoken of as kangaroo-like, the Dinosaurs, many of which attained, enormous proportions. In bigness these greater Dinosaurs have never been exceeded, although the sea can still show in the whales creatures as great. Some of these, and the largest among them, were herbivorous animals; they browsed on the rushy vegetation and among the ferns and bushes, or they stood up and grasped trees with their fore-legs while they devoured the foliage. Among the browsers, for example, were the Diplodocus carnegii, which measured eighty-four feet in length, and the Atlarlosaurus. The Gigantosaurs, disinterred by a German expedition in 1912 from rocks in East Africa, was still more colossal. It measured well over a hundred feet! These greater monsters had legs, and they are usually figured as standing up on them; but it is very doubtful if they could, have supported their weight in this way, out of water. Buoyed up by water or mud, they may have got along. Another noteworthy type we have figured is the Triceratops. There were also a number of great flesh-eaters who preyed upon these herbivores. Of these, Tyrannosaurus seems almost the last word in frightfulness among living things. Some species of this genus measured forty feet from snout to tail. Apparently it carried this vast body kangaroo, fashion on its tail and hindlegs. Probably it reared itself up. Some authorities even suppose that it leapt through the air. If so, it possessed muscles of a quite miraculous quality. A leaping elephant would be a far less astounding idea. Much more probably it waded half submerged in pursuit of the herbivorous river saurians.

 

5.2 Flying Dragons

 

One special development of the dinosaurian type of reptile was a light, hopping, climbing group of creatures which developed a bat-like web between the fifth finger and the side of the body, which was used in gliding from tree to tree after the fashion of the flying squirrels. These bat-lizards were the Pterodactyls. They are often described as flying reptiles, and pictures are drawn of Mesozoic scenery in which they are seen soaring and swooping about. But their breastbone has no keel such as the breastbone of a bird has for the attachment of muscles strong enough for long sustained flying. They must have flitted about like bats. They must have had a grotesque resemblance to heraldic dragons, and. they played the part of bat-like birds in the Mesozoic jungles. But bird-like though they were, they were not birds nor the ancestors of birds. The structure of their wings was altogether different from that of birds. The structure of their wings was that of a hand with one long finger and a web; the wing of a bird is like an arm with feathers projecting from its hind edge. And, these Pterodactyls had no feathers.

 

[Fig 0030 Later Mesozoic Reptiles]

 

[Fig 0030]

 

5.3 The First Birds

 

Far less prevalent at this time were certain other truly birdlike creatures, of which the earlier sorts also hopped and clambered and the later sorts skimmed and flew. These were at first"by all the standards of classification"Reptiles. They developed into true birds as they developed wings and as their reptilian scales became long and complicated, fronds rather than scales, and so at last, by much spreading and splitting, feathers. Feathers are the distinctive covering of birds, and they give a power of resisting heat and, cold far greater than that of any other integumentary covering except perhaps the thickest fur. At a very early stage this novel covering of feathers, this new heat-proof contrivance that life had chanced upon, enabled many species of birds to invade a province for which the pterodactyl was ill equipped. They took to sea fishing"if indeed they did not begin with it"and spread to the north and south polewards beyond the temperature limits set to the true reptiles. The earliest birds seem to have been carnivorous divers and water birds. To this day some of the most primitive bird forms are found among the sea birds of the Arctic and Antarctic seas, and it is among these sea birds that zoologists still find lingering traces of teeth, which have otherwise vanished completely from the beak of the bird.

 

[Fig 0031 Pterodactyls and Archaeopteryx]

 

[Fig 0031]

 

The earliest known bird (the Archaeopteryx) had no beak; it had a row of teeth in a jaw like a reptile's. It had three claws at the forward corner of its wing. Its tail, too, was peculiar. All modern birds have their tail feathers set in a short compact bony rump; the Archaopteryx had a long bony tail with a row of feathers along each side.

 

5.4 An Age of Hardship and Death

 

This great period of Mesozoic life, this second volume of the book of life, is indeed an amazing story of reptilian life proliferating and developing. But the most striking of all the story remains to be told. Right up to the latest Mesozoic Rocks we find all these reptilian orders we have enumerated still flourishing unchallenged. There is no hint of an enemy or competitor to them in the relics we find of their world. Then the record is broken. We do not know how long a time the break represents; many pages may be missing here, pages that may represent some great cataclysmal climatic change. When next we find abundant traces of the land plants and the land animals of the earth, this great multitude of reptile species had gone. For the most part they have left no descendants. They have been wiped out. The pterodactyls have gone absolutely, of the plesiosaurs and ichthyosaurs none is alive; the mosasaurs have gone; of the lizards a few remain, the monitors of the Dutch East Indies are the largest; all the multitude and diversity of the dinosaurs have vanished. Only the crocodiles and the turtles and tortoises carry on in any quantity into Cainozoic times. The place of all these types in the picture that the Cainozoic fossils presently unfold to us is taken by other