Protorosaurus speneri (Seeley 1888) Late Permian ~260 mya, 2 m in length, was originally considered ancestral to lizards, but it is not related according to the large reptile tree. Protorosaurus was derived from a sister to Prolacerta and was itself a sister to Boreopricea and Pamelaria.
The purpored juvenile Protorosaurus (IPB R 535) is actually related to Homoeosaurus, but also from the Late Permian. Another purported Protorosaurus (WMsN P47361) is closer to Pamelaria.
The new lectotype for Protorosaurus (NHMW 1943I4) has no skull but is otherwise complete and articulated. It is small.
The cervicals were massive and slightly longer overall. The dorsal neural spines were taller. That tail had taller neural spines and shorter chevrons.
The scapula was concave anteriorly, losing the plate-like anterior rim found in Prolacerta. The forelimb was more robust with larger unguals.
The pelvis was shorter. The hind limbs was more robust and digit V was not so hook-like.