190 WHEN THE WORLD WAS YOUNG
unearthed at Swindon, but are found far more frequently in the Rocky Mountains. It is, perhaps, quite the most curious in shape of all these strange old animals. Its body forms an arch, with a pair of long solid legs not far from the centre, and another pair of quite little ones near its small head. Right down the middle of its back, stretching from its head to its spiny tail, was a ridge of huge bony plates, like colossal ivy leaves, the centre ones measuring two or three feet across. It seems to have been about twenty-five or thirty feet long; its sense of smell was very acute, its eyes were large, and could absorb much light, and it ought to have been very clever, as it had two sets of brains, one in the usual place, and the other, ten times bigger, near the thigh. As may be imagined, the Stegosaurus (or ' lizard with a roof ') was very heavy to move, and most likely found it pleasanter to pass most of its time in the water, which, being of more weight than the air, would support its great bones better. But when on land it could defend itself from its enemies by the help of its tail, which had four pairs of strong sharp spikes, calculated to keep the most bloodthirsty animal at bay. Its own food, as shown by its teeth, was soft juicy plants.
There is no time to say much of the largest of all the Dinosaurs, which has been found in America, and measured more than eighty feet. Its thigh bone alone was taller than a man, and if it walked upright it would certainly have been thirty feet high. Nor can we linger over the fish lizards, which came before all these, or the lobster-like creatures that lived before them, or over the crocodiles, some eighteen feet long, found in the new red sandstone and later rocks, or over the tapirs, or many more. But we must just glance at a few birds which are now extinct, partly through the merciless hunting down by man, and partly owing to natural causes, with which he has nothing to do.
As far as can be gathered from the rocks, the birds (which did not come into being till the great order of