Tetrapodomorpha

Tetrapodomorpha is a clade within the lobe-finned fishes (sarcopterygians) that includes the tetrapods (amniotes and modern amphibians) and all extinct lineages more closely related to tetrapods than to lungfishes. It represents the evolutionary lineage leading from fish to land-adapted vertebrates and sits on the stem toward crown Tetrapoda. The group originated in the Paleozoic era, with the earliest known tetrapodomorph fossils dating from the Late Silurian to Early Devonian and a major diversification during the Devonian.

Anatomically, tetrapodomorphs are characterized by robust, fleshy fin structures with bones in the fin that are homologous to limb bones in tetrapods (such as upper and lower arm bones and their counterparts in the legs). They typically possess features that foreshadow terrestrial locomotion, including strengthened pectoral and pelvic girdles and fin musculature capable of supporting and maneuvering the body on uneven substrates. Some lineages show adaptations for air exposure and respiration beyond gill-based systems, reflecting a mosaic of aquatic and terrestrial tendencies.

Key fossil taxa illustrate the transition: early stem-tetrapodomorphs such as Eusthenopteron and related rhipidistians, followed by forms like Panderichthys and Tiktaalik, which display increasing limb-like characteristics. True tetrapods such as Acanthostega and Ichthyostega mark the appearance of recognizable terrestrial vertebrates in the Late Devonian. Tetrapodomorpha thus documents a major vertebrate transition from water to land, shaping the subsequent evolutionary history of amphibians, reptiles, birds, and mammals.