Image: Ancestors of the land vertebrates cropped

Description: The delta deposits indicate a warm humid climate with seasonla rainfall producing dry periods and stagnant, vegetation-choked pools. These conditions favored the development of air-breathing freshwater fishes, the Sarcopterygii, from which all higher vertebrates evolved. In one division, the Crossopterygii, the fins have fleshy lobes at their bases. These were forerunners of the libs of terrestrial animals. Air-breathing fish with stout muscular fins, effective both in passage through thick aquatic vegetation and in short land journeys, would have a better chance for survival. The best known of such fish is Eusthenopteron seen here in the foreground.
Title: Ancestors of the land vertebrates cropped
Credit: Wikimedia Commons
Author: Ellen
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