Gansus is a genus of aquatic birds that lived during the Lower Cretaceous period, between 115 to 105 million years ago (mya). It was found 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 related groups, such as Confuciusornis, Ichthyornis and Hesperornis.
Temporal range: Lower Cretaceous, ~110 million years ago
Hou & Liu, 1984 (type)
The genus Gansus contains a single species, G. yumenensis, which was about the size of a pigeon and similar in appearance to loons and diving ducks.  It had many features common among modern birds, and also retained some primitive traits such as its clawed wings.
Gansus was discovered in the form of a single fossil foot in 1981. Five more well-preserved 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 were 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.
- 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.
- 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 2006-06-15.
- You, Hai-lu et al. 2006. A nearly modern amphibious bird from the early Cretaceous of Northwestern China. Science 312: 1640-1643. doi:10.1126/science.1126377 Supporting Online Material
- Norris, Scott (2006-06-15). "Dinosaur-era birds surprisingly ducklike, fossils suggest". National Geographic Society. Retrieved 2006-06-15.