Yanornithiformes is an order of ornithuromorph dinosaurs from the early Cretaceous Period of China. All known specimens come from the Yixian Formation and Jiufotang Formation, dating to the early Aptian age, 124.6 to 120 million years ago.
Naming and early studies The family Songlingornithidae was first named by Hou in 1997 to contain the type genus, Songlingornis.Hou, (1997). Mesozoic Birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp. Clarke et al. (2006) was first to find a close relationship between Songlingornis and the "yanornithids", which had been previously named to contain the similar species Yanornis and Yixianornis. At least one study has found Hollanda from the Late Cretaceous of Mongolia to be a member of this group. The family Yanornithidae (now Songlingornithidae) had been placed in its own order containing no other families, named Yanornithiformes, in 2001.Clarke, Zhou and Zhang, (2006). "Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui." Journal of Anatomy, 208: 287-308. Disputed relationship with the hongshanornithids
Beginning in 2012, multiple studies began to recover the songlingornithids in a clade with the hongshanornithids, a group of smaller, more specialized ornithuromorphs from the same time and place as some of the songlingornithids.O'Connor, J.K. and Zhou Z. (2012). "A redescription of Chaoyangia beishanensis (Aves) and a comprehensive phylogeny of Mesozoic birds." Journal of Systematic Palaeontology, (advance online publication). Other studies however continued to place the hongshanornithids just outside the yanornithiform clade.
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