Hainosaurus ("Hain river lizard") is an extinct genus of marine lizard belonging to the mosasaur family. It was one of the largest mosasaurs, reaching lengths of up to 15 meters (49 ft) which made it one of the top predators of the Late Cretaceous. These animals may have preyed on turtles (Archelon), mosasaurs (Halisaurus), plesiosaurs (Elasmosaurus), pterosaurs (Pteranodon), cephalopods (Tusoteuthis), sharks (Squalicorax) and fish (Xiphactinus).