neither evidence that the material assigned to it is monophyletic (belongs to one species), nor that it is paraphyletic (belongs to several species). This is the case because the holotype of P. (Sellosaurus) gracilis has no skull, and the other specimens consist of skulls and material that overlaps too little with the holotype to make it certain that it belongs to the same taxon. It is therefore possible that the known material contains more species belonging to Plateosaurus. Some scientists regard other species as valid as well, for example P. erlenbergensis and P. engelhardti. These claims are problematic since both P. erlenbergensis and P. engelhardti have undiagnostic type specimens. All named species of Plateosaurus except the type species, P. gracilis, or P. longiceps 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. G. ingens has been considered separate from Plateosaurus, pending a revision of the material. 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