"anningasaura" is known only from the holotype specimen nhmuk 49202, which consists of a complete skull, palate, and mandible, with eight associated cervical vertebrae, including the atlas-axis complex. the partial skeleton came from a juvenile plesiosaur. it was originally referred to ""plesiosaurus" macrocephalus" by charles william andrews in 1896, which is otherwise known only from the very young type specimen nhmuk or1336. nhmuk 49202 was collected at lyme regis, of dorset, from the hettangian to early sinemurian-aged beds of the lower lias group.