Two new ornithurine birds from the Early Cretaceous of western Liaoning, China
We describe two new ornithurine birds from the Early Cretaceous Jiufotang Formation of western Liaoning, northeast China:Yanornis martini gen. et sp. nov. andYixianornis grabaui gen. et sp. nov. They represent the best fossil record of ornithurine birds known from the Early Cretaceous. They are more advanced than the most primitive ornithurineLiaoningornis, and are more similar to the other two Chinese Early Cretaceous ornithurinesChaoyangia andSonglingornis. Compared withConfuciusornis, Liaoxiornis andEoenantiornis from the same age, the two new birds show remarkable advanced characteristics and suggest the presence of powerful flight capability like modern birds. Compared withYixianornis andChaoyangia, Yanornis is larger, with a more elongated skull and relatively long wings. The new discoveries indicate that by the Early Cretaceous both enantiornithine and ornithurine birds had already radiated significantly. The flight structures ofYanornis andYixianornis are hardly distinguishable from those of modern birds; however, both retain a few primitive traits such as teeth on the jaws, wing claws and pubic symphysis, which exclude them from being the most recent ancestor of all extant birds.