Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a taxon of the bony fishes whose members are known as lobe-finned fishes.

What is special about lobe-finned fish?

One of the most important characteristics of lobe-finned fish is the lobe in their fins. Unlike other fish, sarcopterygian fish has a cental appendage in their fins containing many bones and muscles. The fins are very flexible and potentially useful for supporting the body on land, as in lungfish and tetrapods.

What makes a lobe-finned fish?

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The lobe-finned fishes are the sister group to the ray-finned fishes. They are characterized by their paired, fleshy pectoral, and pelvic fins that are each articulated via a single bone. Ancestral records clearly show us that terrestrial vertebrates evolved from lobe-finned fishes nearly 400 million years ago.