Hydrotherosaurus was a carnivorous dinosaur from the Cretaceous Period. Its name means "Fishing Lizard". The Hydrotherosaurus measured approximately 26 ft in length. It has one of the longest necks relative to total length among elasmosaurids, with 60 vertebrae in total. It had a small head that measured about 13 in long, a streamlined body, and four large flippers that were specially designed to help the huge animal balance, move, and accelerate itself.