Callibrachion is an extinct genus of caseid synapsids that lived in east-central France during the Lower Permian (Asselian). The holotype and only known specimen (MNHN.F.AUT490) is represented by an almost complete postcranial skeleton associated with skull fragments discovered at the end of the 19th century in the Permian Autun basin in Saône-et-Loire department, in the Bourgogne-Franche-Comté region. It belongs to an immature individual measuring less than 1.50 m in length. Callibrachion was long considered a junior synonym of the genus Haptodus and classified among the sphenacodontid pelycosaurs. In 2015, a new study found that Callibrachion was a different animal from Haptodus and that it was a caseasaur rather than a sphenacodontid. This was confirmed in 2016 by a cladistic analysis which recovered Callibrachion as a basal caseid. Callibrachion'''s sharp teeth and unenlarged ribcage indicate that this animal was likely faunivorous. Description Callibrachion is known by a relatively complete but poorly preserved skeleton. It is preserved on a black shale slab which exposes the ventral side of the skeleton. The latter consists of a fragmentary skull, the rib cage, the forelimbs, and the right hindlimb. The left hindlimb and tail are missing as well as some parts of the shoulders and pelvis. The exposed notochordal canal and disarticulation of the scapulocoracoid and ilium (where the bony vasculature is visible) indicate an immature ontogenetic stage. In contrast, the well-ossified metapodials indicate that this is not an early juvenile. Although almost complete, no autapomorphies can be identified in Callibrachion due to the generally poor state of preservation of the specimen as well as the great incompleteness of the skull which usually concentrates many distinctive characters. Callibrachion is defined by a combination of characters such as fine and straight conical teeth, moderately thickened ribs, the possible presence of a closed ectepicondylar foramen, an ilium with the high dorsal lamina typical of caseids, robust but not enlarged phalanges, and an unreduced phalangeal formula. The skull is represented by several fragments of which only the maxilla (and possibly a portion of the premaxilla) is an element clearly identifiable by its row of marginal teeth. The ventral margin is slightly convex, with some large caniniform teeth at the anterior end indicated by the broad dental bases unlike the smaller ones preserved posterior to the latter. A second region of enlarged teeth is present posterior to the caniniform positions and is reminiscent of what is observed in eothyridids