Protorosaurus speneri (Spener 1710, von Meyer 1830, Gottmann−Quesada A and Sander PM 2009, RCSHC-Fossil Reptiles 308) Late Permian ~260 mya), is the holotype specimen, known from a disarticulated skull and a partial skeleton.This fossil was one of the first fossil vertebrates described. Originally considered similar to a crocodile, then ancestral to lizards, but it is not related to either.

Protorosaurus speneri (Spener 1710, von Meyer 1830, Gottmann−Quesada A and Sander PM 2009, NHMW 194314 lectotype) Late Permian ~260 mya, up to 2 m in length, Protorosaurus was derived from a sister to Prolacerta and was itself a sister to Boreopricea and Pamelaria, all close to the ancestry of archosauriforms.

The new lectotype for Protorosaurus (NHMW 1943I4, Gottmann−Quesada A and Sander PM 2009) has no skull but is otherwise complete and articulated. 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. Diet included conifer seeds.

The purported 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.

Protorosaurus speneri? (NMK-S-180) includes an excellent skull with a low, wide skull that included a sagittal and nuchal crest.

Evans SE and King MS 1993. A new specimen of Protorosaurus (Reptilia: Diapsida) from the Marl Slate (Late Permian) of Britain. Proceedings of the Yorkshire Geological Society 49, 229–234.

Gottmann−Quesada A and Sander PM 2009. A redescription of the early archosauromorph Protorosaurus speneri Meyer, 1832 and its phylogenetic relationships. Palaeontographica A 287, 123–220.

von Meyer 1830. Isis von Oken, p 518.

von Meyer 1832. Palaeologica pp. 109, 208.

Seeley K 1888. Research on the structure, organisation and classification of the fossil Reptilia 1. On the Protorosaurus speneri (von Meyer). Philosophical Transactions of the Royal Society, London B 178, 187–213.

Spener CM 1710. Disquisitio de crocodilo in lapide scissili expresso, aliisque Lithozois Miscellanea Berolinensia ad incrementum scientiarum ex scriptis Societati Regiae Scientiarum exhibitis 1:92-110.

wiki/Protorosaurus