Los temnospóndilos (Temnospondyli) son un importante grupo extinto de tetrápodos primitivos que prosperaron durante los períodos Carbonífero, Pérmico y Triásico. Unos cuantos linajes sobrevivieron hasta el Cretácico Inferior, siendo Koolasuchus el último temnospóndilo del que se tengan registros. El grupo se originó en el Viseano, a mediados del período Carbonífero Inferior (también conocido como Misisípico) hace aproximadamente 340 millones de años, logrando a lo largo de su historia evolutiva diversificarse y establecerse en un amplio rango de hábitats (tanto acuáticos como semiacuáticos y terrestres) y nichos ecológicos, en especial en el Carbonífero Superior y el Pérmico Inferior. Hacia finales del Pérmico (Lopingiense) y a raíz de la extinción masiva del Pérmico-Triásico, la gran mayoría de los temnospóndilos se extinguieron, sobreviviendo tres linajes relictuales de distribución gondwánica (Dvinosauria y los progenitores de los clados Capitosauria y Trematosauria) que, posteriormente, se diversificaron y repoblaron la tierra a partir del Triásico inferior (Induense). Tras este evento de extinción y hasta la desaparición del grupo en el Cretácico Inferior hace aproximadamente 120 millones de años, los temnospóndilos estuvieron prácticamente restringidos a hábitats acuáticos. Presentaban un carácter cosmopolita, habiéndose descubierto restos fósiles de temnospóndilos a lo largo de todo el mundo, desde Groenlandia hasta el Continente Antártico.

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Temnospondyli (from Greek τέμνειν (temnein, "to cut") and σπόνδυλος (spondylos, "vertebra")) is a diverse subclass of extinct small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including fresh water, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis, and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are considered amphibians, many had characteristics, such as scales, claws, and armour-like bony plates, that distinguish them from modern amphibians. Temnospondyls have been known since the early 19th century, and were initially thought to be reptiles. They were described at various times as batrachians, stegocephalians, and labyrinthodonts, although these names are now rarely used. Animals now grouped in Temnospondyli were spread out among several amphibian groups until the early 20th century, when they were found to belong to a distinct taxon based on the structure of their vertebrae. Temnospondyli means "cut vertebrae", as each vertebra is divided into several parts. Experts disagree over whether temnospondyls were ancestral to modern amphibians (frogs, salamanders, and caecilians), or whether the whole group died out without leaving any descendants. Different hypotheses have placed modern amphibians as the descendants of temnospondyls, another group of early tetrapods called lepospondyls, or even as descendants of both groups (with caecilians evolving from lepospondyls and frogs and salamanders evolving from temnospondyls). Recent studies place a family of temnospondyls called the amphibamids as the closest relatives of modern amphibians. Similarities in teeth, skulls, and hearing structures link the two groups.

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