the dorsal (trunk) vertebrae with two joints, acting together as a simple hinge joint, which has allowed researchers to reconstruct the inhaled and exhaled positions of the ribcage. The difference in volume between these two positions defines the air exchange volume (the amount of air moved with each breath), determined to be approximately 20 L for a P. engelhardti individual estimated to have weighed 690 kg, or 29 mL/kg bodyweight. This is a typical value for birds, but not for mammals, and indicates that Plateosaurus probably had an avian-style flow-through lung, although indicators for postcranial pneumaticity (air sacs of the lung invading the bones to reduce weight) can be found on the bones of only a few individuals, and were only recognised in 2010. Combined with evidence from bone histology this indicates that Plateosaurus was endothermic. The type species of Plateosaurus is P. trossingensis. Adults of this species reached in length, and ranged in mass from . The geologically older species, P. gracilis (formerly named Sellosaurus gracilis), was somewhat smaller, with a total length of . Classification Plateosaurus is a member of a group of early herbivores known as "prosauropods". The group is not a monophyletic group (thus given in quotation marks), and most researchers prefer the term basal sauropodomorph. Plateosaurus was the first "prosauropod" to be described, and gives its name to the family Plateosauridae as the type genus. Initially, when the genus was poorly known, it was only included in Sauria, being some kind of reptile, but not in any more narrowly defined taxon. In 1845, von Meyer created the group Pachypodes (a defunct junior synonym of Dinosauria) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus. Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda. Later it was moved to "Prosauropoda" by von Huene, a placement that was accepted by most authors. Before the advent of cladistics in paleontology during the 1980s, with its emphasis on monophyletic groups (clades), Plateosauridae was defined loosely, as large, broad-footed, broad-handed forms with relatively heavy skulls, unlike the smaller "anchisaurids" and sauropod-like "melanorosaurids". Reevaluation of "prosauropods" in light of the new methods of analysis led to the reduction of Plateosauridae. For many years the clade only included Plateosaurus and various junior synonyms, but later two more genera were considered to belong to it: Sellosaurus and possibly Unaysaurus. Of these, Sellosaurus is probably another junior synonym of Plateosaurus. Basal sauropodomorph phylogeny simplified