Before crocodiles ruled the waters, these giant amphibians dominated the world's ecosystems.

Nature · Published 3 October 2026 Swipe more like this →

In short: Stereospondyli were a diverse group of extinct amphibians that thrived across all seven continents during the Mesozoic. Often filling niches now occupied by crocodilians, these creatures survived the Permo-Triassic mass extinction and persisted in various forms until the Cretaceous, leaving behind a complex fossil record that continues to challenge paleontologists.

Defined in 1888 by Zittel, the Stereospondyli are primarily recognized by their unique vertebral anatomy, where the intercentrum dominates the vertebral structure alongside the neural arch. However, this classification remains fluid; researchers have identified diverse morphologies, such as the diplospondylous condition found in tupilakosaurids and the distinct plagiosaurid arrangement. These amphibians first appeared in the early Permian, with fragmentary remains discovered in Brazil's Pedra de Fogo Formation. While they were once thought to have radiated from high-latitude refugia in Australia or Antarctica following the Permo-Triassic extinction, newer evidence of rhinesuchid communities in South America suggests a potential origin in western Gondwana.

By the end of the Early Triassic, these amphibians had achieved a global presence, with major clades appearing across the fossil record. While many large-bodied stereospondyls were obligately aquatic—evidenced by pachyostotic bone histology, lateral line systems, and occasional gill preservation—others, like the small-bodied lapillopsids, likely possessed greater terrestrial capabilities. Some trematosauroids were even euryhaline, inhabiting marine environments. Their ecological roles were vast; rather than simple crocodile analogs, they occupied varied niches, including those of benthic ambush predators. Bone beds featuring metoposaurids suggest that some species may have aggregated in large groups before mass mortality events.

The group represents the latest-surviving temnospondyls. While most disappeared following the Triassic extinction and the rise of pseudosuchian archosaurs, chigutisaurid brachyopoids lingered into the Jurassic. The youngest known stereospondyl, Koolasuchus, survived until the late Early Cretaceous in Australia. A provocative, though contested, hypothesis suggests that if the Late Triassic North American taxon Chinlestegophis is indeed a stem caecilian, then the lineage of the Stereospondyli has not truly vanished but persists in the form of modern limbless amphibians. This ongoing debate underscores how much remains to be understood about these resilient survivors of the Mesozoic world.

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