File:Ancestors of the land vertebrates cropped.png

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English: 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.
Français : Les dépôts du delta indiquent un climat chaud et humid, aux précipitations saisonnières produisant des périodes sèches et des mares stagnantes et étouffées par la végétation. Ces conditions ont favorisé le développement de poissons d'eau douce à respiration aérienne (les Sarcoptérygii), à partir desquels tous les vertébrés supérieurs ont évolué. Parmi les Sarcoptérygii, les Crossopterygii ont développé des nageoires aux lobes charnus à leurs bases. Ils furent les précurseurs des animaux terrestres. Leur respiration aérienne et des nageoires musclées et robustes leur permettaient de se déplacer dans une végétation aquatique dense, et de faire de courts trajets terrestres, leur donnant de meilleures chances de survie.
Le plus connu de ces poissons est l'Eusthenopteron, visible ici au premier plan.
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Source Wikimedia Commons
Author Ellen

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