National Geographic : 1956 Mar
Some algae and fungi, perhaps two billion years old, also a few sponges, brachiopods, arthropods, and wormlike trails and burrows have been found-and that's about all. This fragmentary chapter contains the most signifi cant part of life's story. Small wonder that young paleontologists dream of unearthing on some unexplored island or remote con tinental tract a fossil sequence that will show how protozoans evolved into trilobites! Like an underwater camera, the fossil se quence records the kaleidoscopic life of Cam brian seas, then moves on to parade primi tive jawless vertebrates, hideous scorpionlike creatures eight feet long, and fantastic ar mored fish. Old species become extinct, new ones rise to dominance. Plants invade the gray barrens of the con tinents. Sharks and bony fishes battle in the oceans. A footprint in Devonian sands records the dramatic moment, some 300 mil lion years ago, when a lunged amphibian ven tured out on a land now mantled with green. Drawing i,> John W. Lothirs 4 Life's Endless Miracle Parades Out of the Mists of Time For ages after earth was born, there was no life. Creation's first stirrings took place in warm primeval seas, but wrote no record in the rocks. Tiny one celled algae and fungi left the earliest evidences of life some two billion years ago. The fossil story remains almost blank until the Cambrian, half a billion years in the past. Marine invertebrates (figures 2 through 8) were already well developed by that period; they live on today in countless species of sponges, corals, worms, mollusks, and crustaceans. First vertebrates were the fishes (9-11), progeni tors of the amphibians (13), whose lungs and limbs enabled them to waddle out on land. Dinosaurs (27, 28, 38), descendants of the amphibians, grew to giant size, only to become extinct, but crocodiles (51) sur vived, as though evolution had stood still. Birds (29) and reptilian pteranodon (39) with its leathery 27-foot wingspread evolved from related cold-blooded stock. Mammals branched off from the reptiles in the Mesozoic. Whale (49), the largest, and man (60), the brainiest of mammals, appeared in the Cenozoic, the era in which we live. Paralleling animals, the vegetable kingdom evolved from primitive seaweeds (1) through ferns (12), cycads (23), conifers (25), and flowering plants (35).