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'''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 of the 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.
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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.
The Ornithurae form 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. A thorough comparison of ''G. yumenensis'' to the Hesperornithes may prove especially fruitful, as the assignment of the latter to the Ornithurae is not altogether certain because of their extreme specialization (e.g. their 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.
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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

Footnotes

1. Waterfowl fossils fill in a big missing link: 110 million-year-old birds bridge gap between age of dinosaurs and today MSNBC
2. Dinosaur-Era Birds Surprisingly Ducklike, Fossils Suggest