Cetiosaurus (SEET-ee-oh-sawr-us) meaning 'whale lizard', from the Greek cetus/κητος meaning 'sea monster' (later, 'whale') and saurus/σαυρος meaning 'lizard', was a sauropod dinosaur from the Mid to Late Jurassic Period (181-169 million years ago) in what are now Europe and Africa. It is estimated to have been about 53 feet (16 m) long and to have weighed roughly 24.8 tonnes (27.3 short tons). It was so named because its discoverer, Sir Richard Owen supposed it was a marine creature, initially an extremely large crocodile.