We have already noted the size of the earlier water scorpions. For long ages such creatures were the supreme lords of life. Then in a division of these Palæozoic rocks called the Silurian division, which many geologists now suppose to be as old as five hundred million years, there appears a new type of being, equipped with eyes and teeth and swimming powers of an altogether more powerful kind. These were the first known backboned animals, the earliest fishes, the first known Vertebrata. SHARKS AND GANOIDS OF THE DEVONIAN PERIOD SHARKS AND GANOIDS OF THE DEVONIAN PERIOD _By Alice Woodward_ These fishes increase greatly in the next division of rocks, the rocks known as the Devonian system. They are so prevalent that this period of the Record of the Rocks has been called the Age of Fishes. Fishes of a pattern now gone from the earth, and fishes allied to the sharks and sturgeons of to-day, rushed through the waters, leapt in the air, browsed among the seaweeds, pursued and preyed upon one another, and gave a new liveliness to the waters of the world. None of these were excessively big by our present standards. Few of them were more than two or three feet long, but there were exceptional forms which were as long as twenty feet. We know nothing from geology of the ancestors of these fishes. They do not appear to be related to any of the forms that preceded them. Zoologists have the most interesting views of their ancestry, but these they derive from the study of the development of the eggs of their still living relations, and from other sources. Apparently the ancestors of the vertebrata were soft-bodied and perhaps quite small swimming creatures who began first to develop hard parts as teeth round and about their mouths. The teeth of a skate or dogfish cover the roof and floor of its mouth and pass at the lip into the flattened toothlike scales that encase most of its body. As the fishes develop these teeth scales in the geological record, they swim out of the hidden darkness of the past into the light, the first vertebrated animals visible in the record. V THE AGE OF THE COAL SWAMPS The land during this Age of Fishes was apparently quite lifeless. Crags and uplands of barren rock lay under the sun and rain. There was no real soil—for as yet there were no earthworms which help to make a soil, and no plants to break up the rock particles into mould; there was no trace of moss or lichen. Life was still only in the sea.