Hyphalosaurus baitaigouensis (Gao, Tang and Wang 1999) Early Cretaceous, ~122mya, ~80 cm in length, was derived from the basal choristodere Cteniogenys and represented the last of its line.
Distinct from Cteniogenys, the skull of Hyphalosaurus was relatively smaller with a shorter rostrum.
The neck was greatly elongated. It included 26 cervicals. Another species of Hyphalosaurus had only 19. The dorsal ribs were thick and the belly was completely covered in long, straight, transversely-oriented gastralia. The tail was elongated. It was wider than tall for the first seven vertebrae, transitioning to taller than wide thereafter.A single scute topped each dorsal vertebra.
The hands and feet resembled those of Lazarussuchus in having digit 4 the longest and all digits tipped in deep, sharp unguals.
In 2007 a rare, two-headed fossil Hyphalosaurus was reported. Hyphalosaurus laid as many as 18 eggs, each without a mineralized shell. The shells were thin and leathery, like those of lizards. This stage can precede live birth as in mammals, lizards, plesiosaurs, mosasaurs and ichthyosaurs.