Hyphalosaurus (meaning "submerged lizard") is a genus of freshwater aquatic reptiles which represent a major part of the Jehol Biota. They lived during the early Cretaceous period (Aptian age), about 122 million years ago. The genus contains two species, H. lingyuanensis and H. baitaigouensis, both from the Yixian Formation of Liaoning Province, China.