The Jiufotang overlays the Yixian, which suggests an Aptian or Albian age (between 100-120 million years old), according to Swisher et al. (1999).
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Paul Sereno et al. (2001) considered a similar prehistoric bird species from the same formation, Cathayornis, to be a junior synonym of Sinornis.
Paul Sereno et al., in 2002, considered Cathayornis a junior synonym of Sinornis.
It was first defined as a clade in 1998 by Paul Sereno, who made it the group of all birds closer to living birds than to Enantiornithes (represented by Sinornis).