[N] 2011 Xiaotingia zhengi
Xu, X., You, H., Du, K. & Han, F. (2011) An Archaeopteryx-like theropod from China and the origin of Avialae. Nature Vol, 475 465-470 [Xiaotingia zhengi]
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China.
This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs). Notably, adding the new taxon into a comprehensive phylogenetic analysis shifts Archaeopteryx to the Deinonychosauria.
Despite only tentative statistical support, this result challenges the centrality of Archaeopteryx in the transition to birds. If this new phylogenetic hypothesis can be confirmed by further investigation, current assumptions regarding the avialan ancestral condition will need to be re-evaluated.
An initial cladistic analysis by Xu et al. showed that Xiaotingia zhengi formed a clade with Archaeopteryx , the Dromaeosauridae and the Troodontidae to the exclusion of other forms traditionally seen as birds. Xu et al. therefore (re)defined the concepts of Deinonychosauria and Avialae to the extent that Archaeopteryx and Xiaotingia belonged to the Deinonychosauria and Archaeopteryx no longer was an avialan.
This led to popular reports that \\\\\\\"Archaeopteryx is no longer a bird\\\\\\\", though Xu et al. noted that there are several competing definitions of the clade Aves currently in use, pointing out that their definitions are compatible with a traditional Aves with Archaeopteryx as a specifier. However, this was challenged by a more thorough analysis published several months later, in which Archaeopteryx was again recovered as an avialan, while Xiaotingia remained closely allied to Anchiornis within the Troodontidae.