Hyphalosaurus is a genus of freshwater aquatic reptiles, belonging to the extinct order Choristodera. They lived during the early Cretaceous period, about 122 million years ago. The genus contains two species, H. lingyuanensis and H. baitaigouensis, both from the Yixian Formation of Liaoning Province, China. 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.
Hyphalosaurus
Juvenile H. lingyuanensis
Fossil specimen of H. baitaigouensis
H. baitaigouensis fossils displayed in the Hong Kong Science Museum
Choristodera is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the Miocene. Choristoderes are morphologically diverse, with the best known members being the crocodile-like neochoristoderes such as Champsosaurus. Other choristoderans had lizard-like or long necked morphologies. Choristoderes appear to have been confined to the Northern Hemisphere, having been found in North America, Asia, and Europe, and possibly also North Africa. Choristoderes are generally thought to be derived neodiapsids that are close relatives or members of Sauria.
Image: Philydrosaurus proseilus NMNS
Image: Ikechosaurus sp. NMNS (cropped)
Skeleton of Champsosaurus natator at the Canadian Museum of Nature
Skeletons of Hyphalosaurus, in the collections of the Beijing Museum of Natural History (BMNH)