New ornithuromorph bird material from the Lower Cretaceous Yixian Formation of Weichang, Hebei Province, China

New Ornithothoraces fossil material was recovered during a systematic survey of fossil and geological heritage resources from the Lower Cretaceous Yixian Formation of Chedaogou locality, Weichang County, Hebei Province, northeastern China. The specimen preserves several dorsal vertebrae and an articulated pelvic girdle. Detailed morphological analysis reveals a specimen with the following significant anatomical features: the synsacrum is composed of 8-9 fused vertebrae; the pelvic girdle is well fused with a developed antitrochanter; the ilium is relatively broad, with the postacetabular region significantly shorter than the pre-acetabular region; the ischium is broad and shallowly arcuate, slightly bending ventrally and lacking a distinct dorsal process in the middle and with a non-pointed distal margin; and the pubis is slender and cylindrical, with a relatively uniform diameter, lacking a pubic boot and with unfused distal ends. These features probably indicate a new ornithuromorph species. This discovery enriches our understanding of avian diversity in Jehol Biota, providing an important specimen for studying the evolution of the pelvic girdle in Mesozoic birds. Additionally, the result of this geological survey shows the Yixian Formation disconformity with the underlying Zhangjiakou Formation at Chedaogou locality, suggesting a discontinuous deposition in the research area.