largely unprepared until 2003. The few overlapping elements with Euromycter suggested that it belongs to a different taxon named Ruthenosaurus russellorum in 2011. Description Ruthenosaurus is diagnosed by several autapomorphies including dorsal vertebrae with anteriorly tilting neural spines and a diamond-shaped outline in transverse section; a first sacral rib with robust distal head, twice that of the second sacral rib; and a short iliac blade with prominent posterior process. It can be distinguished from Euromycter, from older deposits of the same locality, by the shape of the distal part of the humerus, including an ectepicondylar notch rather than a fully enclosed foramen, the specific shape of the ulna, and the overall robustness of the specimen. The lack of fusion of the neural arches with their respective vertebral centra and incomplete ossification of the ends of the limb elements, including the absence of an ossified olecranon on the ulna, show clearly that this specimen represents a juvenile individual. However, it is distinctly larger than the fully mature specimen of Euromycter, suggesting a very large size for adult Ruthenosaurus. Stratigraphic range The holotype of Ruthenosaurus was found in the uppert part of the red pelitic beds of the M2 Member, which belongs to the Grès Rouge (“Red Sandstone”) Group, a sedimentary sequence subdivided into five hectometric members (M1 to M5) localized in the western Rodez basin. Like the M1 Member that has yielded Euromycter, the deposits of the M2 Member are interpreted as a playa-lake environment (or Sabkha) under a semi-arid, hot climate. The age of the Grès Rouge Group is uncertain but it is regarded as contemporaneous to the Saxonian Group of the neighbourhing Lodève basin, where radiometric and magnetostratigraphic data suggested previously an age between the late Sakmarian (middle of the Early Permian) and the early Lopingian (early Late Permian). However, new chronostratigraphic and magnetostratigraphic data for the Saxonian Group indicate an age between the Artinskian (for the Rabejac Formation and the Octon Member of the Salagou Formation) and the late Roadian-Wordian and possibly early Capitanian (for La Lieude Formation). A more precise stratigraphic correlation of the permian Rodez basin with that of Lodève was proposed in 2022 by Werneburg and colleagues. In the Rodez basin, the FII Formation of the Salabru Group, underlying the Grès Rouge Group, yielded palynomorphs, conchostracans, and a tetrapod footprints assemblage equivalent to that of the Viala Formation of the Lodève basin. The lower part