Recent macroevolutionary studies predict a diversification of early birds during the Jurassic period1–4, but the unquestionable Jurassic bird fossil record is limited to Archaeopteryx1,5,6, which has also been referred to deinonychosaurian dinosaurs by some analyses7,8. Although they have feathered wings, the known Jurassic birds are more similar to non-avialan theropods in having the ancestral long reptilian tail9–11. This is in stark contrast to most Cretaceous and crownward taxa, which have a short tail that terminates in a compound bone called the pygostyle12–14. Here we report on the oldest short-tailed avialan, Baminornis zhenghensis gen. et sp. nov., from the recently discovered Late Jurassic Zhenghe Fauna15, which fills a noticeable spatio-temporal gap in the earliest branching avialan fossil record. B. zhenghensis exhibits a unique combination of derived ornithothoracine-like pectoral and pelvic girdles and plesiomorphic non-avialan maniraptoran hand, demonstrating mosaic evolution along stem avialan line. An avialan furcula collected from the same locality is referrable to ornithuromorphs on the basis of our morphometric and phylogenetic analyses. These newly discovered fossils demonstrate the early appearance of highly derived bird features, and together with an anchiornithine fossil from the same locality, they suggest an earlier origin of birds and a radiation of early birds in the Jurassic.
