The Triassic @-@ Jurassic extinction event around 199 @.@ 6 Mya led to the extinction of most Mesozoic temnospondyls . The brachyopoids survived , as well as a few capitosauroids and trematosauroids . While the latter two groups soon became extinct , brachyopoids persisted and grew to large sizes during the Jurassic . Among brachyopoids , the brachyopids flourished in China and the chigutisaurids became common in Gondwana . The most recent known temnospondyl was the giant chigutisaurid Koolasuchus , known from the Early Cretaceous of Australia . It survived in rift valleys that were too cold in the winter for crocodiles that normally would have competed with them . Koolasuchus was one of the largest of the brachyopoids , with an estimated weight of 500 kg ( 1 @,@ 100 lb ) .