Alex Soares Ribeiro, age12, of Montreal, Que., Canada, for his question:
WHAT WERE THE PALEOZOIC SEA CREATURES LIKE?
No doubt there were earlier creatures, but they left no fossils to show us what they were like. The Paleozoic sea dwellers came later and many of them had shells and even bones. The oldest known fossils came from the seas of the ancient Paleozoic Era.
The word Paleozoic means ancient life, so one would expect the creatures of those far off times to be smallish and rather simple. However, there were a few surprises, including a jawless fish with a skeleton and a water scorpion nine feet long.
The Paleozoic Era began about 600 million years ago and lasted through more than 300 million years. So let's expect tofind some enormous advances and variations in this first long chapter of life on earth. For example, when it began, the land was bare. When it closed, there were swampy coal forests, populated with insects, amphibians and early reptiles. It was a mild era and shallow seas often slopped over much of the land. Our eastern and western mountains were unborn.
The sunny shallow seas were less salty and the Paleozoic creatures had all the time in the world to improve themselves. From the beginning there were sponges and polyps, jellyfish and assorted sea worms. Corals had plenty of time to build reefs and offshore islands. And the waters teemed with assorted algae.
During the first 100 million years or so, the most advanced creatures were the trilobites, arthropod ancestors of our shrimps and insects. The first backboned animal was a jawless fish, who arrived with the mollusks about 480 million years ago.
Then came the sharks and the fish family branched out in assorted shapes and sizes. The Age of the Trilobites began to wane and the last of these ancestral arthropods died out with the Paleozoic Era. Meantime, about 400 million years ago, the Age of Fishes began. For a while they were the most advanced creatures on the earth.
After 200 million years of struggling to survive and improve, life in the sea was well established. The next great strides forward came with the plants and animals that left the ancient seas and established life on the dry land.