"Vertebrates are derived from a very primitive Precambrian marine arthropod, the stage before compound eyes were evolved. Vertebrates arose from its free-swimming larval stage, and their organs evolved, through those of the protarthropod, from those of the annelid. The evolution and deployment of the lower fishes (s.l.) are sketched. The first vertebrates evolved mainly in fresh water within one or more river basins of perhaps a 'north-Atlantic' continent, though before this their ancestors were marine."

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