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How did the fins of ancient fishes contribute to the evolution of land vertebrate limbs?

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Least tern, Sternula antillarum, flying with wings raised and its yellow-tipped black bill pointed forward. — Locomotion These birds largely reside in coastal areas of North America, although some populations live in the continent's interior along large rivers.

The evolution of land vertebrate limbs from the paired fins of ancient fishes is a transition rooted in the anatomy of sarcopterygian (lobe-finned) fishes.123

Structural Transition

The limbs of tetrapods share a common pattern with the paired fins of lobe-finned fishes, which possessed internal skeletal support extending beyond the body's muscle mass. During the transition, which occurred over 80 million years, the fin-ray sections declined and were eventually replaced by skeletal elements. This process involved the development of joints—such as the elbow, knee, wrist, and ankle—that allowed for bending rather than simple curving.23

Functional Evolution

Initially, these appendages likely functioned as supportive struts for movement along the bottom of shallow water bodies rather than for weight-bearing on land. As these animals spent more time in terrestrial environments, natural selection favored a more robust, tightly linked skeleton to counter the effects of gravity. This included the firm anchoring of the pelvic girdle to the vertebral column and the detachment of the pectoral girdle from the skull to facilitate neck flexibility and improved steering.23