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Evolution The process by which all living things have developed from primitive life forms through changes occurring over billions of years is evolution. All living things arose through a long history of changes formed by physical and chemical processes that are still taking place. It is possible that all organisms can be traced back to the origin of life from inanimate matter. Paleontology is the most direct proof of evolution because it studies life of …

…largely barren of animal life. However, the seas were crowded with many invertebrates, cartilaginous and bony fish. A prominent bony fish, the Crossopterygii, possessed the ability to rise to the surface and gulp air. This fish was one of the first amphibians. What led the Crossopterygii to venture on to land is still under speculation by scientists. The Crossopterygians were crudley adapted for land existance but bacause they had no competitors they survived. They possessed