Fig. 4: Selected axial elements of Confuciusornis shifan holotype (PMoL-AB00178).

a cervical vertebrae. b synsacrum. c pygostyle. sy synsacrum. Arrows in b and c indicate the longitudinal ridge on the ventral surface of the synsacrum and the positions of foramina along the pygostyle, respectively. Also see Supplementary Fig. 1 for a close-up of the distal part of the pygostyle. Scale bars: 0.5 cm in a, c; 1 cm in b.