Wikipedia
Caudipteridae is a family of oviraptorosaurian dinosaurs known from the Early Cretaceous of China. Found in the Yixian and Jiufotang Formations, the group existed between 125-120 million years ago. Distinguishing characteristics of this group have been indicated as including a unique dagger-shaped pygostyle (the bone at the tip of the tail in birds, used to anchor a "fan" of feathers). No clade definition has been given.
The first caudipterid described was Caudipteryx zoui (named in 1998), though the family itself was not named until the discovery of a second species, Caudipteryx dongi, in 2000. Caudipteridae was restricted to the single genus Caudipteryx and was therefore monotypic, containing only a single type and often considered redundant. However, in 2008 Similicaudipteryx yixianensis was described and classified as a caudipterid.