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