Lariosaurus fossil. Fossilised remains of a Lariosaurus sp. dinosaur. Lariosaurus were primitive marine nothosaur reptiles that lived during the Triassic period (250-200 million years ago). They grew up to just 60 centimetres long and as such were one of the smallest known nothosaurs. They were unique among nothosaurs as the front legs were adapted into paddles, while the back legs remained five-toed.