Fig. 3
From: The Concept of Co-option: Why Evolution Often Looks Miraculous
The evolution of the tetrapod forelimb mapped onto a simplified phylogenetic tree for the lobe-finned fishes (Sarcopterygii). It is important to note that the bones identified on this phylogeny (e.g., the humerus, radius, phalanges) continued to be modified past their point of origin. The main point, though, remains the same—the tetrapod limb evolved in an aquatic environment and not as an adaptation for living on land. ✞ = extinct species