Gansus

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iGansus Fossil range: Early Cretaceous
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Genus: Gansus Hou & Liu, 1984
Binomial name
Gansus yumenensis Hou & Liu, 1984

Gansus is a genus of aquatic birds that lived during the Albian stage of the Early Cretaceous period (around 110 million years ago) in what is now Gansu province, western China. It is the oldest-known Ornithurae, the group which includes modern birds (Neornithes) and extinct relatives groups, such as Ichthyornithes and Hesperornithes.

The genus contains a single species, G. yumenensis, which was about the size of a pigeon and similar in appearance to loons and diving ducks. ^[1] It had most modern bird features, with exceptions such as its lack of hollow bones, and its clawed wingtips, both of which may have impaired its flight slightly. This bird is the oldest-known member of the Ornithurae (a clade which contains all living birds and their closest relatives).

All extant birds, including taxa as diverse as ostriches, hummingbirds and eagles, are descended from basal Ornithurans. It is now thought entirely possible that all birds descended specifically from a semi-aquatic bird similar to Gansus. Thus, while Gansus is not necessarily a direct ancestor of today's birds, it is closely related to such an ancestral species. It is the oldest modern bird known to date. Especially a thorough comparison of G. yumenensis to the Hesperornithes may prove fruitful, as the assignment of the latter to the Ornithurae ist not altogether certain because of their extreme specialization (e.g. near-complete loss of wings and feet that were carried splayed sidewards).

Previously known from only a single fossil foot discovered in 1981, five well-preserved Gansus fossils were found in 2003–2004, in mudstone at the site of an ancient lake at Changma, Gansu; the geological stratum in which the fossils are found is the Xiagou Formation. Their bodies had settled in anoxic mud and were soon covered with further extremely fine silty sediments; without oxygen, their remains resisted decay: these specimens preserved remains of flight feathers and traces of the webbing between their toes. ^[2]

[edit] References

• Hou, L. & Liu, Z. (1984): A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Sci. Sin. Ser. B 27: 1296−1302.
• You, Hai-lu; Lamanna, Matthew C.; Harris, Jerald D.; Chiappe, Luis M.; O'Connor, Jingmai; Ji, Shu-an; Lü, Jun-chang; Yuan, Chong-xi; Li, Da-qing; Zhang, Xing; Lacovara, Kenneth J.; Dodson, Peter & Ji, Qiang (2006): A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China. Science 312: 1640-1643. DOI: 10.1126/science.1126377 HTML abstract Supporting Online Material
• http://www.theglobeandmail.com/servlet/story/RTGAM.20060615.woldbird0615/BNStory/Science/home

[edit] Footnotes

1. ^ MSNBC (2006-06-15). Waterfowl fossils fill in a big missing link: 110 million-year-old birds bridge gap between age of dinosaurs and today. Retrieved on 2006-06-15.
2. ^ Norris, Scott (2006-06-15). Dinosaur-Era Birds Surprisingly Ducklike, Fossils Suggest. National Geographic Society. Retrieved on 2006-06-15.