Bird display both clearly traditional reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. The earliest known avialan fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include "Anchiornis huxleyi", "Xiaotingia zhengi", and "Aurornis xui". The well-known early avialan, "Archaeopteryx", dates from slightly later Jurassic rocks
Archaeopteryx common uses of that term. A more thorough analysis was published soon after to test this hypothesis, and failed to arrive at the same result; it found "Archaeopteryx" in its traditional position at the base of Avialae, while "Xiaotingia" was recovered as a basal dromaeosaurid or troodontid. The authors of the follow-up study noted that uncertainties still exist, and that it may not be possible to state confidently whether or not "Archaeopteryx" is a member of Avialae or not, barring new and better specimens of relevant species. Phylogenetic studies conducted by Senter, "et al." (2012) and Turner, Makovicky, and Norell