The surangular enclosed two mandibular fenestrae. The hindmost part of the surangular had a small foramen placed in the same position as similar openings in the mandibles of non-bird theropods and modern birds. The splenial bone was three-pronged (as in some modern birds, but unlike the simple splenial of Archaeopteryx), and its lower margin followed the lower margin of the mandible. There was a large rostral mandibular fenestra and a small, rounded caudal fenestra behind it. Though only five specimens preserve parts of the beak's keratinous covering, these show that there would have been differences between species not seen in the skeleton. The holotype of C. dui preserves the outline of an upwards curving beak which sharply tapers towards its tip, while a C. sanctus specimen (IVPP V12352) has an upper margin that is almost straight, and a tip that appears to be slightly hooked downwards. Two further specimens (STM13-133 and STM13-162) belonging to an indeterminate species were described in 2020; the former suggests that, unlike modern birds, the beak on both jaws was made up of two separate elements that met at the midline, with feathers growing between them on the upper jaw. Also unlike modern birds, these specimens suggest that the upper beak extended backwards onto the maxilla due to the presence of foramina. Postcranial skeleton The various specimens seem to have a variable number of neck vertebrae, some showing eight, others nine. The first vertebra, the atlas, bore a faint keel on the underside. The next, the axis, had an expanded spinal process on the top and its side was excavated by an elongated groove in the side. The remaining neck vertebrae all had rather low spinal processes. There is no clear evidence of a pneumatisation, in the form of internal air spaces, of the vertebral bodies of the neck. The front articulation facets of the neck vertebrae were saddle-shaped. Their undersides were pinched. There were at least twelve back vertebrae. They were amphiplatian, flat at both ends, and had rather small intervertebral foramina, the spaces between the vertebral body and the neural arch. Their spinal processes were tall and narrow in side view. Their side processes projected horizontally and were deeply excavated at the rear underside. The sides of the back vertebrae also had deep oval excavations. Seven sacral vertebrae were fused into a synsacrum. The front sacral vertebra had a round and concave front articulation