Sapeornis chaoyangensis (Zhou and Zhang 2002. 2003; Early Cretaceous; IVPP V13276) is a basal ornithurine bird, the clade that gave rise to modern birds. The short tail was tiped with a pygostyle. The coracoids were wide and relatively short. Manual digit 3 is a vestige. The claws on the remaining digits are all raptorial.
DNHM-F3078 (Gao et al. 2012 (Figs 1, 2) was smaller, considered a juvenile based on bone texture. It lived 3-5 million years earlier and had a pubic boot. It nests with the IVPP specimen in the LRT.
As a reminder…
None of these sapeornithid birds had an ossified sternum.
Gao C, Chiappe LM, Zhang F, Pomeroy DL, Shen C, Chinsamy A and Walsh MO 2012. A subadult specimen of the Early Cretaceous bird Sapeornis chaoyangensis and a taxonomic reassessment of sapeornithids. Journal of Vertebrate Paleontology. 32(5): 1103–1112.
Zhou Z and Zhang F-C 2003. Anatomy of the primitive bird Sapeornis chaoyangensis from the Early Cretaceous of Liaoning, China. Canadian Journal of Earth Sciences 40(5): 731–747.
A clade that contains all modern birds (regardless of which definition of the name Ornithurae you’re using – under only one of them is Sapeornis a member of Ornithurae).