Mastodonsaurus & Early Triᴀssic Sea Monsters: Giant Amphibians and the Rise of Marine Reptiles After the Permian Extinction

Following the devastating Permian-Triᴀssic mᴀss extinction 252 million years ago, Earth’s oceans recovered slowly. In the Early Triᴀssic, giant temnospondyl amphibians such as Mastodonsaurus giganteus became the dominant aquatic predators, reaching lengths of up to 6 metres with mᴀssive, flat skulls and powerful jaws filled with dagger-like teeth.

These “mastodon lizards” (named for their enormous size) inhabited rivers, lakes, and coastal lagoons across what is now Europe and North America. Their fossils, especially from Germany’s Buntsandstein, show they were ambush hunters capable of taking large fish, other amphibians, and even early reptiles. Unlike modern amphibians, these Triᴀssic giants retained powerful limbs and could move on land when necessary.

At the same time, the first true marine reptiles began to appear. Thalattosaurs and early ichthyosaurs such as Cymbospondylus quickly colonised the open ocean, while marine temnospondyls like Trematosaurus and Aphaneramma adapted to fully marine life with elongated snouts and paddle-like limbs.

By the Middle Triᴀssic (~240 Ma), these amphibian “sea monsters” were gradually replaced by more specialised reptiles. The Early Triᴀssic thus marks a unique transitional phase when giant amphibians briefly ruled the recovering oceans before the Age of Marine Reptiles truly began.

These fossils, housed in European museums, demonstrate how life rebounded after the worst extinction in Earth’s history — with bizarre, oversized amphibians leading the way.