Ambiortiformes is a group of prehistoric ornithuromorph

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

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 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...

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 is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

. ''A. dementjevi'' belongs to the Ornithuromorpha (the group containing modern birds but not

enantiornithes The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct Avialae, avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teet ...

), according to all published

cladistic Cladistics ( ; from Ancient Greek 'branch') 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 ...

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 Ornithurae (meaning "bird tails" in Greek) is a natural group that includes modern birds and their very close relatives such as the ichthyornithines and the hesperornithines. This clade is defined in the ''PhyloCode'' by Juan Benito and collea ...

, 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 Formation ...

'' 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, Liaoning, Chaoyang (People's Republic of China) dated to the early Aptian age, ...

''.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 avialan 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 ...

''. 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

{{Taxonbar, from=Q16687464 Euornithes Bird clades Cretaceous dinosaurs Dinosaurs of Mongolia