All named species of Plateosaurus except the type species and P. gracilis have turned out to be junior synonyms of the type species or invalid names.
Von Huene practically erected a new species and sometimes a new genus for each relatively complete find from Trossingen (three species of Pachysaurus and seven of Plateosaurus) and Halberstadt (one species of Gresslyosaurus and eight of Plateosaurus).
Later, he merged several of these species, but remained convinced that more than one genus and more than one species of Plateosaurus was present in both localities.
Jaekel also believed that the Halberstadt material included several plateosaurid dinosaurs, as well as non-plateosaurid prosauropods.
Systematic research by Galton drastically reduced the number of genera and species.
Galton synonymised all cranial material, and described differences between the syntypes of P. engelhardti and the Trossingen material, which he referred to P. longiceps.
Galton recognised P. trossingensis (P. fraasianus and P. integer are junior objective synonyms) to be identical to P. longiceps.
Markus Moser, however, showed that P. longiceps is itself a junior synonym of P. engelhardti.
Furthermore, a variety of species in other genera were created for material belonging to P. engelhardti, including Dimodosaurus poligniensis, Gresslyosaurus robustus, Gresslyosaurus torgeri, Pachysaurus ajax, Pachysaurus giganteus, Pachysaurus magnus and Pachysaurus wetzelianus.

The skull of AMNH FARB 6810, the best-preserved skull of Plateosaurus that has been taken apart during preparation and is thus available as separate bones, was described anew in 2011.
The authors of that publication, palaeontologists Albert Prieto-Márquez and Mark A. Norell, refer the skull to P. erlenbergensis, a species erected in 1905 by Friedrich von Huene and regarded as a synonym of P. engelhardti by Markus Moser.
If the P. erlenbergensis holotype is diagnostic (i.e., has enough characters to be distinct from other material), it is the correct name for the material assigned to P. longiceps Jaekel, 1913.

Aside from fossils clearly belonging to Plateosaurus, there is much prosauropod material from the German Knollenmergel in museum collections, most of it labeled as Plateosaurus, that does not belong to the type species and possibly not to Plateosaurus at all.
Some of this material is not diagnostic; other material has been recognised to be different, but was never sufficiently described.
All named species of Plateosaurus except the type species and P. gracilis have turned out to be junior synonyms of the type species or invalid names. Von Huene practically erected a new species and sometimes a new genus for each relatively complete find from Trossingen (three species of Pachysaurus and seven of Plateosaurus) and Halberstadt (one species of Gresslyosaurus and eight of Plateosaurus). Later, he merged several of these species, but remained convinced that more than one genus and more than one species of Plateosaurus was present in both localities. Jaekel also believed that the Halberstadt material included several plateosaurid dinosaurs, as well as non-plateosaurid prosauropods. Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material, and described differences between the syntypes of P. engelhardti and the Trossingen material, which he referred to P. longiceps. Galton recognised P. trossingensis (P. fraasianus and P. integer are junior objective synonyms) to be identical to P. longiceps. Markus Moser, however, showed that P. longiceps is itself a junior synonym of P. engelhardti. Furthermore, a variety of species in other genera were created for material belonging to P. engelhardti, including Dimodosaurus poligniensis, Gresslyosaurus robustus, Gresslyosaurus torgeri, Pachysaurus ajax, Pachysaurus giganteus, Pachysaurus magnus and Pachysaurus wetzelianus.
The skull of AMNH FARB 6810, the best-preserved skull of Plateosaurus that has been taken apart during preparation and is thus available as separate bones, was described anew in 2011. The authors of that publication, palaeontologists Albert Prieto-Márquez and Mark A. Norell, refer the skull to P. erlenbergensis, a species erected in 1905 by Friedrich von Huene and regarded as a synonym of P. engelhardti by Markus Moser. If the P. erlenbergensis holotype is diagnostic (i.e., has enough characters to be distinct from other material), it is the correct name for the material assigned to P. longiceps Jaekel, 1913.
Aside from fossils clearly belonging to Plateosaurus, there is much prosauropod material from the German Knollenmergel in museum collections, most of it labeled as Plateosaurus, that does not belong to the type species and possibly not to Plateosaurus at all. Some of this material is not diagnostic; other material has been recognised to be different, but was never sufficiently described.
Plateosaurus