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.

The exposed notochordal canal and disarticulation of the scapulocoracoid and ilium (where the bony vasculature is visible) indicate an immature ontogenetic stage.

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.

[2] 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 and in the basal caseid Martensius.

[2] The vertebral column is represented by about twelve centra of dorsal vertebrae, as well as uncertain remains of the cervical series and neural arches.

[2] The holotype of Callibrachion was discovered in the 19th century in the Margenne site during oil shale mining then in progress in the Autun basin.

The palaeontological richness of this basin allowed at the time to define the Autunian as a reference stage for the continental Lower Permian of Europe.

Based on plant, invertebrate, and amphibian fossils, the Autunian was considered to be an age equivalent to the global marine stages of the late Gzhelian, Asselian, Sakmarian, and Artinskian.

The middle part of the Igornay Formation is dated at 299.9 ± 0.38 Ma and represents the late Gzhelian (latest Carboniferous), confirming the first age estimates of the oldest Autunian levels.

The Lally oil shale bed in the lower part of the Muse Formation is dated at 298.91 ± 0.08 Ma, which corresponds, at ± 100,000 years, to the Carboniferous-Permian boundary set in the marine strata in the Ural Mountains.

[6] The rare amniotes found in these lacustrine layers, such as Callibrachion, the small sphenacodontid Haptodus and the taxon of uncertain affinity “Belebey” augustodinensis[nb 3][9][10] (both known from another site in the same formation) are allochthonous.

[14] Callibrachion lacked the enlarged rib cage of derived herbivorous caseids which had a voluminous intestine necessary for digestion of high-fiber vegetation.

[15] It was not until 2015 that the animal was re-studied by Spindler and colleagues and identified as a caseasaur on the basis of its overall proportions as well as dental and osteological characteristics that exclude it from any other synapsid clades.