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Some identifiable distant relatives of life on earth

Posted in Animals, Historical articles, History, Nature, Prehistory on Thursday, 28 February 2013

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This edited article about prehistory originally appeared in Look and Learn issue number 166 published on 20 March 1965.

Prehistory, picture, image, illustration

Eocene, Oligocene and Miocene periods saw the evolution of animal species which appear more familiar to us today

By the time of the Eocene period, which began about 70 million years ago, the reign of the giant reptiles called dinosaurs was over. They had roamed the earth for about 125 million years, and over that period they had seen the birth of the great mountain systems – Himalayas, Andes, and Rockies had all raised their crags above the surrounding land.

They had witnessed the development of broad-leafed trees; they had watched the first flowers bloom, and heard the thunder of the seas as they advanced and retreated over huge land areas.

Why did the great lizards die away? There is no one satisfactory answer to this. There was no great change of vegetation at the time of their disappearance, nor did the climate apparently alter.

One thing we do know. In relation to their vast bulk, the dinosaurs had tiny brains. Perhaps the giant reptiles’ nerve centres became unable to cope with their unwieldy bodies, causing whole species to die . . . but this is only a theory.

Curiously enough one of the larger Eocene land creatures was a bird, the dyatryma. This feathered monster stood seven feet high, and like today’s ostrich, it could not fly.

The term Eocene comes from the two Greek words: eos meaning “dawn” and kainos meaning “new.” It certainly was the dawn of a new period of animal life.

Unlike the dinosaurs, which laid eggs, most Eocene animals were mammals, that is, the young were born alive and were suckled by their mother.

Eocene reptiles included big crocodiles which wallowed in the mud of a sub-tropical estuary where London stands today.

When the Oligocene period began 40 million years ago the mammals were firmly established and the ancestors of nearly all of the animals we know had appeared; hence the name oligocene, which comes from two Greek words, oligos, meaning “little,” and kainos, meaning new.

One very curious fact about the early mammals was that most of them were very small in size compared with the dinosaurs. Few of them were bigger than rabbits and many of them were rat size of even smaller.

Eohippus, from which our horse is descended, was no bigger than a fox. Unlike the horse however, it had several hooved toes instead of a single large one.

Indeed, it was the small size of the first mammals that enabled them to survive when they had been developing in the time of the dinosaurs.

Being so tiny they could live unnoticed by the giant reptiles and they needed much less food. They could move more quickly than could the lumbering brontosaurus and its huge relatives and could lie hidden in burrows. Above all, they were warm blooded and had fur instead of scales, so that they kept warm in a colder world.

Not that the Oligocene period was without its giants. One of these was the brontotherium, which was a distant relative of the rhinoceros and horse. It was about the size of today’s rhinoceros and had a thick hide and twin horns on the nose.

During the Miocene period, which began 25 million years ago, the mammals had become much bigger than in Oligocene times. The tiny eohippus had developed into the merychippus, which was still smaller than a pony but much more horse-like, with reduced side toes which did not touch the ground.

Then there was the slightly bigger procamelus, which is thought to have been the ancestor of today’s camel and llama. Birds, too, were becoming more plentiful.

Vegetation was becoming more like that of today, and there were forests of oak, beech, maple, walnut, chestnut, elm and plane trees very little different from those we know.

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