Lobe-finned fish

Lobe-finned fish are vertebrates whose paired fins contain fleshy lobes supported by internal bones. The group includes coelacanths, lungfishes, and tetrapods.

Sarcopterygii: A vertebrate clade comprising lobe-finned fishes and their descendants, including tetrapods. This is the taxonomic group defined by lobe-bearing paired fins.
Fin-to-limb transition: The evolutionary transformation of vertebrate paired fins into limbs with digits. Lobe-finned fossils document anatomical stages in this transition.
Devonian: A geological period from about 419 to 359 million years ago, marked by major fish diversification. Many early lobe-finned fossils come from this period.
Ray-finned fish: Fishes whose paired fins are supported mainly by slender rays rather than fleshy bony lobes. They form the contrasting major lineage of living bony fishes.
Paired fins: Fins occurring as left-right pairs, such as pectoral and pelvic fins. Lobe-finned anatomy is a distinctive form of paired-fin structure.
Acanthostega: An extinct Devonian tetrapod with digits that was still adapted to aquatic life. Its limbs show that digits appeared before fully terrestrial locomotion.
Eusthenopteron: An extinct Devonian lobe-finned fish known from fossils in Canada. Its fin bones resemble the arrangement later seen in tetrapod limbs.
Cartilaginous fish: Fishes, including sharks and rays, whose skeletons are primarily made of cartilage. Their cartilage-based skeleton contrasts with the bony fin supports of lobe-finned fish.
Pectoral fin: A paired fin located behind the head, corresponding evolutionarily to the forelimb of tetrapods. Its internal bones reveal how a fin could become a forelimb.
Lungfish: A living lobe-finned fish that can breathe air using lungs. Lungfish demonstrate how lobe-finned anatomy persists in living aquatic vertebrates.

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