Ambiortiformes is a group of prehistoric

ornithuromorph Euornithes (from Greek ' meaning "true birds") is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to ''Sinornis''. Description Clarke ''et al''. (2006) found that the most primitive know ...

s. The first species to be included, '' Ambiortus dementjevi'', lived sometime during the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...

age between 136.4 and 125 million years agoHoltz, Thomas R. Jr. (2012). ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix
(PDF). in today's

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

. ''A. dementjevi'' belongs to the Ornithuromorpha (the group containing modern birds but not enantiornithes), according to all published

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses. However, the exact position of the species within this group has been controversial. Most analyses have found it to be either an unresolved member of the Ornithurae, or a more primitive member of Ornithuromorpha. One 2006 study, for example, found it to be more primitive than ''

Yanornis ''Yanornis'' () is an extinct genus of fish-eating Early Cretaceous birds. Two species have been described, both from Liaoning province, China: ''Yanornis martini'', based on several fossils found in the 120-million-year-old Jiufotang Formati ...

'' but more advanced than '' Hongshanornis'', or even a member of the specific group containing both ''Yanornis'' and ''

Yixianornis ''Yixianornis'' (meaning "Yixian Formation bird") is a bird genus from the early Cretaceous period. Its remains have been found in the Jiufotang Formation at Chaoyang (People's Republic of China) dated to the early Aptian age, around 120 millio ...

''.You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, (2006). "A nearly modern amphibious bird from the Early Cretaceous of Northwestern China". ''Science'', 312: 1640-1643. The group includes at least ''Ambiortus'' and possibly the supposed close relative ''

Apsaravis ''Apsaravis'' is a Mesozoic bird genus from the Late Cretaceous. The single known species, ''Apsaravis ukhaana'', lived about 78 million years ago, in the Campanian age of the Cretaceous period. Its fossilized remains were found in the Camel's ...

''. The results of a

analysis published in 2011 indicate that ''Apsaravis'' and '' Palintropus'' are very closely related.Longrich, N.R., Tokaryk, T., and Field, D.J. (2011). "Mass extinction of birds at the Cretaceous/Paleogene (K/Pg) boundary". ''Proceedings of the National Academy of Sciences'', 108(37): 15253-15257. .

References

Prehistoric euornitheans Early Cretaceous first appearances Late Cretaceous extinctions {{Theropod-stub