Stephanosaurus (meaning "crown lizard"[1]) is a dubious genus of hadrosaurid dinosaur with a complicated taxonomic history.

In 1902, Lawrence Lambe named a new set of hadrosaurid limb material and other bones (originally GSC 419) from Alberta as Trachodon marginatus.

[2] Paleontologists began finding better remains of hadrosaurids from the same rocks in the 1910s, in what is now known as the late Campanian-age (Upper Cretaceous) Dinosaur Park Formation.

Lambe assigned two new skulls to T. marginatus, and based on the new information, coined the genus Stephanosaurus for the species in 1914.

Because there was very little to associate the complete skulls with the scrappy earlier marginatus material, in 1923 William Parks proposed a new genus and species for the skulls, with both generic and specific names honoring Lambe: Lambeosaurus lambei (type specimen NMC 2869, originally GSC 2869).