fintolimb

Fintolimb is a hypothetical concept used in discussions of vertebrate evolution to describe a transitional stage between the fin of fish and the limb of tetrapods. The term combines fin and limb to highlight the idea that limb evolution was gradual, involving incremental changes in skeletal structure, girdles, and musculature.

In the fintolimb model, early fin skeletons would progressively ossify into paired limb bones, with radials and fin rays rearranged to form stylopod, zeugopod, and autopod-like segments, while girdle elements (pectoral and pelvic) enlarge to support weight-bearing locomotion. It is important to note that fintolimb is not a named fossil taxon or an officially recognized anatomical category; rather, it is a didactic shorthand used to illustrate the continuum from aquatic to terrestrial life.

In the evolutionary narrative, the fin-to-limb transition is evidenced by a sequence of fossil forms (for example, early sarcopterygian fishes, and transitional tetrapods such as Tiktaalik, Acanthostega, and Ichthyostega) that display mixtures of aquatic and terrestrial traits. The fintolimb concept helps learners picture these mosaic anatomies, but it remains a simplification, as actual evolutionary steps likely varied across lineages.

See also: Tetrapod, Fin-to-limb transition, Tiktaalik, Acanthostega, Panderichthys.

Further reading: general vertebrate embryology and paleontology texts on limb evolution.