Aspects of this topic are discussed in the following places at Britannica.
By the Late Devonian the earliest tetrapods had appeared. Forms such as Ichthyostega and Acanthostega (both from eastern Greenland) are the best-known. Aptly described as fish with legs, they are classified as labyrinthodont amphibians, which retained many fishlike features, including gills, up to eight digits per foot, and a tail fin...
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