Protorosaurus ("first lizard"), a lizard-like reptile of the order Prolacertiformes, is the earliest known archosauromorph. It lived during the Late Permian period in Germany. In 1914, a new ceratopsian dinosaur found by Lawrence Lambe was again given the name Protorosaurus (in this sense meaning "before Torosaurus"). When Lambe found that the name had already been used for the early archosauromorph, he renamed his ceratopsian Chasmosaurus.
In Geopark of Paleorrota, Rio Grande do Sul, Brazil, 3 vertebrae and some bones of the animal were found.
Protorosaurus grew up to 2 metres (6.6 ft) in length, and was a slender, lizard-like animal, with long legs and a long neck. Its body form suggests that it was fast-moving, although it may have fed primarily on insects. Protorosaurus was closely related to Czatkowiella from the Early Triassic of Poland.