Dinosaurus is an extinct genus of enigmatic therapsids that lived during the Middle Permian in what is now Russia. Initially described as a species of the related genus Rhopalodon by Gotthelf Fischer von Waldheim in 1845, the taxon was assigned its own genus by the same author two years later under the new combination D. murchisonii. The only known specimen consists of cranial remains belonging to a single individual discovered in a copper mine of the former Orenburg Governorate, west of the Ural Mountains. The animal's generic name refers to the supposedly "wild and voracious" nature, while the specific name honours the Scottish geologist Roderick Murchison. Despite its name, Dinosaurus is not a dinosaur; like Dimetrodon, it belongs to the clade Synapsida and is therefore more closely related to mammals than to dinosaurs, the latter being sauropsids.
History of study
The holotype and only known specimen of Dinosaurus was discovered in the early 1840s in the Klyuchevskiy-1 copper mine, located in the Belebeyevsky District within the Orenburg Governorate of the Russian Empire, on the western slopes of the Ural Mountains. This locality was initially dated to the Late Permian, before later being reassigned to the Middle Permian. The specimen originally consisted of a portion of the mandible associated with the left side of the upper jaw, both belonging to the anterior region of the skull. Two years later, Fischer described a third fossil which he considered to belong to the same species, but sufficiently distinct to justify the erection of a new genus. As the animal was regarded as "wild and voracious", he established the genus Dinosaurus. In 1848, the German naturalist Karl Eduard von Eichwald demonstrated that the fragments previously described by Fischer actually belonged to a single skull. Nevertheless, he reassigned the species to Rhopalodon, considering that the observed differences were not yet sufficient to justify a separate genus. Eichwald also pointed out that the name Dinosaurus was very similar to Dinosauria, a reptile taxon created a few years earlier by the British palaeontologist Richard Owen in 1842, and therefore regarded the generic name as potentially preoccupied. However, such a similarity between two scientific names does not in itself constitute a valid reason for nomenclatural invalidation.
thumb|right|alt=|Holotype skull of [[Phthinosuchus discors, a taxon once regarded as a junior synonym of Dinosaurus.]]
Due to the discovery of numerous therapsid fossils in the Klyuchevskiy-1 mine, the validity of Dinosaurus was questioned by several authors over the following decades. In 1894, the British paleontologist Harry Govier Seeley notably suggested that Cliorhizodon (now regarded as a junior synonym of the anteosaurid Syodon) could not be distinguished from Dinosaurus. In 1954, the Russian paleontologist Ivan Yefremov in turn proposed that Dinosaurus and Rhopalodon should be regarded as junior synonyms of Brithopus. Although this interpretation was later followed by some authors, it was rejected by others, who pointed out that Brithopus is based solely on a partial and non-diagnostic humerus, rendering the taxon a nomen dubium. In the absence of directly comparable or associated fossil material with the remains assigned to Dinosaurus, they considered this synonymy impossible to demonstrate reliably. In 2000, the Russian palaeontologist Mikhail F. Ivakhnenko synonymised Phthinosuchus discors with Dinosaurus, arguing that the much more complete holotype skull of the former anatomically corresponded to the cranial fragments known for the latter. However, in 2011, the American paleontologist Christian F. Kammerer noted that the very limited anatomical data available for Dinosaurus make any definitive confirmation of this proposed synonymy difficult.
See also
- Gresslyosaurus – Originally was to be called "Dinosaurus"