Yanornis

Taxobox
name = "Yanornis"
fossil_range = Early Cretaceous
regnum = Animalia
phylum = Chordata
classis = Aves
subclassis = Ornithurae
ordo = Yanornithiformes
familia = Songlingornithidae
genus = "Yanornis"
genus_authority = Zhou & Zhang, 2001
subdivision_ranks = Species
subdivision =
*"Y. martini" Zhou & Zhang, 2001 (type)
synonyms =
* "Archaeovolans" Czerkas & Xu, 2002

"Yanornis" was an Early Cretaceous bird, thought to be closely related to the common ancestor of all modern birds. One species, "Yanornis martini", ["Yanornis", from the Ancient Chinese Yan dynasties, whose capital was at Chaoyang, and Ancient Greek "ornis", "bird". "martini", dedicated to avian paleontologist Larry D. Martin.] has been described from fossils found in the Jiufotang Formation at Chaoyang, Western Liaoning province, PRC, and as of 2004 five specimens were known. [Zhou "et al." (2002)] The age of the Jiufotang Formation is somewhat unclear, but most estimates point towards an early Aptian origin, about 125-120 million years ago.

It was the size of a large pigeon, had a long skull with about 10 teeth in the upper and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula (wishbone). It ate fish, [Zhou "et al." (2004)] and in the associated adaptations shows remarkable convergent evolution to the unrelated enantiornithine "Longipteryx". [Zhou & Zhang (2001)] Furcula and teeth, on the other hand, are more like in the enantiornithine "Aberratiodontus".Gong "et al." (2004)]

The absence of the prefrontal bone and the non-diapsid skull place "Yanornis" into the Ornithurae which also includes the common ancestor of living birds. Similarly, its scapula and coracoid had evolved the basic shape and layout as in modern birds; enable "Yanornis" to lift its wings far above its back for an efficient upstroke. It thus was a more efficient flyer compared to Enantiornithes (which have the modern condition in a less well developed form), let alone "Confuciusornis" which like "Archaeopteryx" was only marginally able to perform an upstroke. [Senter (2006)] To allow for the necessarily large flight muscles, its sternum was longer than wide, again representing an essentially modern condition, as did many features of its arm skeleton.

Taxonomy and systematics

"Yanornis" gained notoriety when the front half of a fossil bird was combined with the tail of a "Microraptor" to make the paleontological forgery "Archaeoraptor". Upon discovering this, the bird half was described as "Archaeovolans repatriatus", which was later found to be a junior synonym of "Yanornis". See "Archaeoraptor".

In a 2006 study of early bird relationships, it was found that "Yanornis", "Yixianornis", and "Songlingornis" formed a monophyletic group; since "Songlingornis" was the first of these birds to be described, the family containing this group is Songlingornithidae. [Mortimer (2004), Clarke "et al." (2006)] The order Yanornithiformes has been erected to mark their distinctness from other early Ornithurae such as "Gansus", but might be called Songlingornithiformes; especially if the present taxon is indeed a junior synonym of "Songlingornis" as sometimes proposed. On the other hand, other analyses seem to suggest that these two genera were well distinct. [Mortimer (2004)]

Footnotes

References

* (2006): Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of "Yixianornis grabaui". "Journal of Anatomy" 208 (3):287-308. DOI|10.1111/j.1469-7580.2006.00534.x [http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1469-7580.2006.00534.x PDF fulltext] [http://www.blackwell-synergy.com/doi/suppl/10.1111/j.1469-7580.2006.00534.x/suppl_file/JOA534_a3.xls Electronic Appendix]
* (2004) Enantiornithine Bird with Diapsidian Skull and Its Dental Development in the Early Cretaceous in Liaoning, China. "Acta Geologica Sinica" 78(1): 1-7. [http://www.paper.edu.cn/downloadpaper.php?serial_number=gongenpu-3&type=2 PDF fulltext]
* (2004): The Theropod Database: [http://home.comcast.net/~eoraptor/Phylogeny%20of%20Taxa.html Phylogeny of taxa] . Retrieved 2008-AUG-14.
* (2006): Scapular orientation in theropods and basal birds, and the origin of flapping flight. "Acta Palaeontologica Polonica" 51(2): 305–313. [http://www.app.pan.pl/acta51/app51-305.pdf PDF fulltext]
* (2001): Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. "Chinese Science Bulletin" 46 (15): 1258-1264. [http://www.ivpp.ac.cn/pdf/magazine192.pdf PDF fulltext]
* (2002): Archaeoraptor's better half. "Nature" 420:285. DOI|10.1038/420285a (HTML abstract) [http://www.nature.com/nature/journal/v420/n6913/suppinfo/420285a.html Supplementary information]
* (2004): Gastroliths in "Yanornis": an indication of the earliest radical diet-switching and gizzard plasticity in the lineage leading to living birds?. "Naturwissenschaften" 91:571-574. [http://www.meas.ncsu.edu/faculty/clarke/publications/ZhouClarZhaWing2004.pdf PDF fulltext]