The Chinese team claims the fossils dated to 155 million years ago (mya), whereas the Solnhofen limestone where Archaeopteyx was found is 144 mya in age. The new fossil Xiaotingia cannot be dated so accurately, as they were originally been purchased from a dealer. Prof Xu first saw the specimen at the Shandong Tianyu Museum. The other question to be asked of all early dinobirds is: could they fly?
A cladistic analysis by Xu and his team showed that Xiaotingia formed a clade with Archaeopteryx, the Dromaeosauridae and the Troodontidae. This clade excludes other birds. They therefore (re)defined the concepts of Deinonychosauria and Avialae so Archaeopteryx and Xiaotingia belonged to the Deinonychosauria and Archaeopteryx no longer was an avian (bird). This led to popular reports that "Archaeopteryx is no longer a bird".
- McGrath, Matt 2011. Feathers fly in first bird debate. BBC Science 
- Xing Xu, Hailu You, Kai Du and Fenglu Han (28 July 2011). "An Archaeopteryx-like theropod from China and the origin of Avialae". Nature 475: 465–470. doi:10.1038/nature10288. http://www.nature.com/nature/journal/v475/n7357/full/nature10288.html.