Hyphalosaurus (meaning "submerged lizard") is a genus of freshwater aquatic reptiles, belonging to the extinct order Choristodera. They lived during the early Cretaceous period (late Barremian to early Aptian age), about 123-120 million years ago. The genus contains two species, H. lingyuanensis from the Yixian Formation and H. baitaigouensis from both the Yixian and Jiufotang Formation of Liaoning Province, China.[1] They are among the best-known animals from the Jehol Biota, with thousands of fossil specimens representing all growth stages in scientific and private collections.