The geological record of marine creatures is vastly richer than that of land creatures. The first fishes appeared in the oceans some 525 million years ago in the late Cambrian period, and evolved quickly to dominate the oceans until today. Their success was so extraordinary that all land vertebrates including, of course, us humans, evolved from them.

Some species of fish have evolved very little since the Paleozoic era hundreds of millions of years ago.

The hagfish, for example, and the better-known lamprey, maintain many characteristics of those first primitive fishes, such as the lack of jaws. However, undoubtedly the most celebrated living fossil is the coelacanth, a rare fish that lives on the Indian Ocean seafloor and was believed to have become extinct 251 million years ago, until in 1933 some fishermen caught a specimen off the coast of South Africa

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