and in the basal caseid Martensius. It is not possible to provide an exact number of teeth or an estimate of the jaw length because the outline of the bone is uncertain. Preserved teeth have a thin, conical crown with a smooth surface, devoid of any significant curvature except in the anterior part of the preserved tooth row. The mandible is represented by a thin and rather shallow branch of the right jaw. Its preserved length of around 70 mm could be close to its original length, as large and slightly curved teeth are found in what is most likely the end of the dentary. The vertebral column is represented by about twelve centra of dorsal vertebrae, as well as uncertain remains of the cervical series and neural arches. The tail is not preserved. Two barely visible cervical centra appear to lie between the skull and the shoulder girdle. Some vertebrae have been damaged during preparation, while others are covered by the shoulder girdle. Nevertheless, thanks to the articulation of the skeleton, it is possible to provide an estimate of the presacral number. In particular, the uninterrupted series of approximately 21 dorsal ribs indicates a minimum presacral number of 23 vertebrae. The ribs are robust. In the posterior dorsal region, the ribs decrease in length, but not in width. The limbs are also strong. A distinctive feature is the scapula much shorter than the humerus. The two manus are fairly well preserved and articulated. The bones of the manus are strong and well developed. However, the metacarpals and phalanges do not exhibit the stocky and enlarged morphology of derived caseids. Their proportions are rather similar to those observed in Eocasea, Martensius, and Casea broilii. The digit IV is the longest in the series. One of its middle phalanges is shortened, measuring about 70% of the length of neighbouring phalanges. Terminal phalanges are strongly curved, with a strong flexor tubercle and an enlarged flat dorsal roof. The manus exhibits the plesiomorphic condition of early amniotes with a phalangeal formula of 2-3-4-5-3. The preserved elements of the right pes are for the most part disarticulated. It is not possible to precise its phalangeal formula, but the individual elements seem to be as robust and strongly developed as those of the manus. Stratigraphic range The holotype of Callibrachion was discovered in the 19th century in the Margenne site during oil shale mining then