have been found in the lakebottom sediments of the Yixian Formation in China, dating to 125 million years ago.
formation | Command (military formation) | Elliot Formation | Lance Formation | Crato Formation | Chinle Formation | Yixian | Two Medicine Formation | Tamayama Formation | Missing Man Formation (band) | Missing Man Formation | Marcellus Formation | Kirkwood Formation | Gettysburg Formation | Clarens Formation | Whitby Mudstone Formation | Tunbridge Wells Sand Formation | Santana Formation | Phalanx formation | phalanx formation | Mahantango Formation | Leduc Formation | Identity formation | Hanson Formation | Formation (stratigraphy) | formation (stratigraphy) | Formation | Centre International de Formation Européenne | Bakken formation | Yixian Formation |
On 7th June 2013, however, Science Magazine published an article which noted that Pascal Godefroit, the paleontologist who led the team that described Aurornis, reported that he is uncertain if the fossil material came from Liaoning province's 160-million-year-old Tiaojishan Formation, as the information provided by the fossil dealer indicated, or from the province's 125-million-year-old Yixian Formation, which is known to have produced several ancient bird fossils.