''Ambiortus'' is a prehistoric

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

. The only known

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''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 preceded ...

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 the

Andaikhudag Formation The Andaikhudag Formation, in older literature referred to as Unduruh Formation or Ondorukhaa Formation, is an Early Cretaceous (Hauterivian to Barremian) geologic formation in Mongolia.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, ...

. It was discovered by

Yevgeny Kurochkin Yevgeny Nikolayevich Kurochkin (Евгений Николаевич Курочкин; 12 July 1940 - 13 December 2011) was a Russian paleornithologist at the Paleontological Institute of the Russian Academy of Sciences. He served as President of t ...

in 1982.

Classification

''Ambiortus dementjevi'' belongs to the

Ornithuromorpha 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 ...

(the group containing modern birds but not

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

), according to all published cladistic analyses. However, the exact position of the species within this group has been controversial. Early studies suggested it was a member of the

Palaeognathae Palaeognathae (; ) is a infraclass of birds, called paleognaths, within the class Aves of the clade Archosauria. It is one of the two extant infraclasses of birds, the other being Neognathae, both of which form Neornithes. Palaeognathae contai ...

, the group containing modern

ratite A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites. The systematics ...

s and

Tinamou Tinamous () form an order of birds called Tinamiformes (), comprising a single family called Tinamidae (), divided into two distinct subfamilies, containing 46 species found in Mexico, Central America, and South America. The word "tinamou" come ...

,Kurochkin, (1985). "A true carinate bird from Lower Cretaceous deposits in Mongolia and other evidence of Early Cretaceous birds in Asia." ''Cretaceous Research'', 6: 271-278. but this has not been supported by later research. Some studies have found it to be closely related to the

Ichthyornithes Ichthyornithes is an extinct group of toothed avialans very closely related to the common ancestor of all modern birds. They are known from fossil remains found throughout the late Cretaceous period of North America, though only two genera, ''Ich ...

, a relatively derived group closely related to

modern birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight s ...

.Kurochkin (1999). "The relationships of the Early Cretaceous ''Ambiortus'' and ''Otogornis'' (Aves: Ambiortiformes)". pp. 275-284 in Olson (ed.), ''Avian Paleontology at the Close of the 20th Century: Proceedings of the 4th International Meeting of the Society of Avian Paleontology and Evolution. Smithsonian Contributions to Paleobiology'', 89. However, most analyses have found it to be either an unresolved member of the

Ornithurae Ornithurae (meaning "bird tails" in Greek) is a natural group which includes the common ancestor of ''Ichthyornis'', ''Hesperornis'', and all modern birds as well as all other descendants of that common ancestor. Classification Ernst Haeckel coi ...

, or a more basal 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, People's Republic of China, China: ''Yanornis martini'', based on several fossils found in the 120-million-ye ...

'' but more advanced than ''

Hongshanornis ''Hongshanornis'' is a genus of ornithuromorph birds known from early Cretaceous lake deposits of the Yixian Formation, Inner Mongolia, China. The holotype specimen, recovered in 2005, is currently held by the Institute of Vertebrate Paleontology ...

'', 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 million ...

''.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

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Ambiortidae is sometimes used for this genus, especially if it is considered a close relative of the much younger ''

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 ...

''. (2011): The Theropod Database
Phylogeny of taxa
. Retrieved 2013-03-02. The results of a cladistic analysis published in 2011, on the other hand, indicate that at least ''Apsaravis'' and ''

Palintropus ''Palintropus'' is a prehistoric bird genus from the Late Cretaceous. A single species has been named (''Palintropus retusus'') based on a proximal coracoid from the Lance Formation of Wyoming, dated to the latest Maastrichtian, million years ag ...

'' (which was mistaken as a much more modern bird initially) 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

Bird genera Early Cretaceous birds of Asia Fossil taxa described in 1982 Prehistoric euornitheans {{paleo-bird-stub