View source for Biology:Apsaravis

{{Short description|Extinct genus of birds}}
{{Speciesbox
| fossil_range = [[Earth:Late Cretaceous|Late Cretaceous]], {{fossil range|78}}
| genus = Apsaravis
| parent_authority = Norell & Clarke, 2001
| species = ukhaana
| authority = Norell & Clarke, 2001
}}

'''''Apsaravis''''' is a [[Earth:Mesozoic|Mesozoic]] [[Biology:Bird|bird]] [[Biology:Genus|genus]] from the Late [[Earth:Cretaceous|Cretaceous]]. The single known species, '''''Apsaravis ukhaana''''', lived about 78 million years ago, in the [[Earth:Campanian|Campanian]] age of the Cretaceous period.  Its [[Biology:Fossil|fossil]]ized remains were found in the Camel's  Humps sublocality of the Djadokhta Formation,  at Ukhaa Tolgod in the [[Earth:Gobi Desert|Gobi Desert]] of Mongolia. They were collected in the 1998 field season by the Mongolian Academy of Sciences/American Museum of Natural History Paleontological Expeditions. It was described by Norell and Clarke (2001).<ref name="Norell&Clarke2001">Norell, Mark A., Clarke, Julia A. (2001). "Fossil that fills a critical gap in avian evolution". ''Nature'' Vol. 409 11 January 2001 pp.181-184.</ref>

Its habitat was presumably very [[Earth:Arid|arid]] open landscape much like it is today, perhaps hotter still and with more (but nonetheless intermittent) rain. Permanent freshwater would have been scarce.

==Implications==
''Apsaravis'' is important in avian paleontology. It has provided evidence that is directly relevant to at least four issues:

=== Sauriurae ===

The [[Biology:Sauriurae|Sauriurae]] are a putative clade of  primitive birds that includes  ''[[Biology:Archaeopteryx|Archaeopteryx]]'',  ''[[Biology:Confuciusornis|Confuciusornis]]'', and [[Biology:Enantiornithes|Enantiornithes]]. It is thought  by Feduccia and Martin to be phylogenetically separate from the Ornithurae and, thus, from modern birds.<ref name="Martin83"/> ''Apsaravis'' has  features of both Sauriurae and Ornithurae. ''Apsaravis'' has several characters that place it near [[Biology:Aves|Aves]] (sensu Gauthier), including the presence of at least ten [[Biology:Sacrum|sacral]] vertebrae, a pubis and ischium that are closely appressed, distal pubes that do not touch, an 'obturator flange' on the ischium, loss of the cuppedicus muscle fossa on the ilium, a patellar groove on the distal [[Biology:Femur|femur]], an anterior sternal keel, completely heterocoelus vertebrae, curved scapular shaft, and several features of the forelimb, ankle, and foot. Apsaravis also retains primitive characters shared with Enantiornithes and more basal theropods, including a narrow intercondylar groove and barrel-shaped [[Biology:Condyle|condyle]]s of the [[Biology:Tibiotarsus|tibiotarsus]], a dorsal fossa of the coracoid, into which the supracoracoideus nerve [[Biology:Foramen|foramen]] opens, and several features of the [[Biology:Humerus|humerus]]. This intermediate anatomy is evidence against the validity of the clade "Sauriurae".<ref name=Clarke&Norell2002>Clarke, Julia A., Norell, Mark A. (2002). "The morphology and phylogenetic position of ''Apsaravis ukhaana'' from the Late Cretaceous of Mongolia". ''American Museum Novitates'', No. 3387, American Museum of Natural History, New York, NY.</ref>

===Enantiornithine monophyly===
In their cladistic analyses, Clarke and Norell (2002) found that ''Apsaravis'' had a mixture of primitive and advanced characters (described above in "Sauriurae") that removed most of the supporting characters for the clade [[Biology:Enantiornithes|Enantiornithes]]. Twenty-seven characters have been used to support enantiornithine monophyly, but ''Apsaravis'' brings the number down to only four. The discovery of further basal ornithurine fossils like ''Apsaravis'' could render the Enantiornithes paraphyletic. This would mean that, rather than a radiation of primitive birds separate from the radiation that led to modern birds, "enantiornithines" would actually be steps along the way to becoming modern birds.<ref name=Clarke&Norell2002/>

===Ecological bottle neck ===
Prior to the discovery of ''Apsaravis'',  most ornithurine birds had been found in marine, lacustrine, or littoral sediments. This led Feduccia (1996)<ref name="Feduccia96">Feduccia,  Alan (1996). ''The origin and evolution of birds''. New Haven, CT: Yale University Press. 420pp.</ref> and Martin (1983)<ref name="Martin83 ">Martin, Larry D. (1983). "The origin and early radiation of birds" pp.291-338 in ''Perspectives on Ornithology'' Brush, A.H., Clark, G.A. New York: Cambridge University Press</ref> to deduce that the ancestors of modern birds were restricted to aquatic environments, and that they were all basal members of the [[Biology:Charadriiformes|Charadriiformes]]. Because they believed that all such birds had a "shorebird ecology", they described this limited habitat as an "ecological bottleneck", with all other ecological niches being dominated by enantiornithine birds instead. ''Apsaravis'', however, was found in a sand dune environment, and it has no obviously aquatic anatomical adaptations, giving clear evidence that not all early members of Ornithurae were shorebirds.<ref name=Clarke&Norell2002/>

=== Automatic extension of the manus ===

''Apsaravis'' is the most basal bird that possesses an extensor process. This is a bony projection on metacarpal I that develops at the insertion of the m.extensor metacarpi radialis muscle and the propatagial ligaments. This anatomy functions to "automate" extension of the [[Biology:Manus (anatomy)|manus]] during extension of the forelimb in [[Biology:Aves|Aves]]. This is a key function for the flight stroke of modern birds.<ref name=Clarke&Norell2002/>

==Phylogenetic position==
Clarke and Norell (2002) found that ''Apsaravis'' is the most basal ornithurine bird,  but more advanced than  [[Biology:Enantiornithes|Enantiornithes]] and  ''[[Biology:Patagopteryx|Patagopteryx]]''.<ref name = Clarke&Norell2002/>

Subsequent cladistic analysis indicates that it and the more advanced ''[[Biology:Palintropus|Palintropus]]'' &ndash; long believed to be a modern bird &ndash;, and perhaps ''[[Biology:Ambiortus|Ambiortus]]'' with which the preceding two had occasionally been allied, form a distinct lineage. This has been named "Palintropiformes", but Apsaraviformes was proposed earlier for the ''Apsaravis'' lineage and is thus the senior synonym. And if this group is held to include ''Apatornis'' too, it would receive the name Ambiortiformes, which was proposed even earlier.

==Footnotes==
{{Reflist}}

==References==
* {{smallcaps|Mortimer, Michael}} (2004): The Theropod Database: [https://web.archive.org/web/20130516175802/http://archosaur.us/theropoddatabase/Phylogeny%20of%20Taxa.html Phylogeny of taxa]. Retrieved 2013-MAR-02.

{{Taxonbar|from=Q4782167}}

[[Category:Bird genera]]
[[Category:Prehistoric euornitheans]]

{{Sourceattribution|Apsaravis}}