Apsaravis
| Apsaravis Temporal range: Late Cretaceous (Campanian)
| |
|---|---|
Fossil
| |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Subclass: | |
| Family: | |
| Genus: | Apsaravis
|
| Species: | A. ukhaana
|
| Binomial name | |
| Apsaravis ukhaana | |
Apsaravis is a Mesozoicbird 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 Humps sublocality of the Djadokhta Formation, at Ukhaa Tolgod in the 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).[1]
Its habitat was presumably very arid open landscape much like it is today, perhaps hotter still and with more (but nonetheless intermittent) rain. Permanent freshwater would have been scarce except in oases.
Implications
Apsaravis is important in avian Paleontology . It has provided evidence that is directly relevant to at least four issues;
Sauriurae
The Sauriurae is a putative clade of primitive birds that includes Archaeopteryx, Confuciusornis, and Enantiornithes. It is thought by Feduccia and Martin to be phylogenetically separate from the Ornithurae and, thus, from modern birds.[2] Apsaravis has features of both Sauriurae and Ornithurae. Apsaravis has several characters that place it near Aves (sensu Gauthier), but it also retains primitive characters shared withEnantiornithes and more basal theropods. This intermediate anatomy is evidence against the validity of the clade "Sauriurae". [3]
Enantiornithine monophyly
(See Enantiornithes) 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 cladeEnantiornithes. 27characters have been used to support enantiornithine monophyly, but Apsaravis brings the number down to only 4. The discovery of further basal ornithurine fossils like Apsaravis could render the Enantiornithes paraphyletic. This would mean that, rather than a radiation of birds separate from the radiation that led to modern birds, enantiornithines" would actually be steps along the way to becoming modern birds.[3]
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) [4] and Martin (1983) [5] to deduce that the ancestors of modern birds were restricted to aquatic environments, and that they were all basal members of the Chradriiformes. 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. [3]
Automatic extension of the manus
Lastly, 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 teh manus during extansion of the forelimb in Aves. This is a key function for the flight stroke of modern birds.[6]
Phylogenetic Position
Clarke and Norell (2002) found that Apsaravis is the most basal ornithurine bird, but more advanced than Enantiornithes and Patagopteryx.[3]
Mortimer's (2004) cladistic analysis confirms that Apsaravis is in the lineage that led to modern birds, together with the famous Gansus yumenensis for example, but not especially close to Ambiortus. Mortimer found it to be a not-too-distant relative of the common ancestor of all living birds. [7]
Footnotes
- ^ 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,.
- ^ Cite error: The named reference
martin83was invoked but never defined (see the help page). - ^ a b c d 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 10024.
- ^ Feduccia, Alan. (1996) "The origin and evolution of birds"New Haven, CT:Yale University Press 420pp.
- ^ Martin, Larry D. (1983) "The origin and early radiation of birds" pp.291-338in "Perspectives on Ornithology" Brush, A.H., Clark, G.A. New York: Cambridge University Press
- ^ Cite error: The named reference
ClarkeandNorell2002was invoked but never defined (see the help page). - ^ Mortimer (2004)
References
- Mortimer, Michael (2004): The Theropod Database: Phylogeny of taxa. Retrieved 2007-OCT-29.
 | This prehistoric bird article is a stub. You can help Wikipedia by expanding it. |