Gansus

Gansus is a genus of aquatic birds that lived during the Aptian age of the Early Cretaceous (Aptian-Albian) period in what are now Gansu and Liaoning provinces, western China. The rock layers from which their fossils have been recovered are dated to 120 million years ago. It was first described in 1984 on the basis of an isolated left leg. It is the oldest-known member of the Ornithurae, the group which includes modern birds (Neornithes) and extinct related groups, such as Ichthyornis and Hesperornithes.

Description

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. In 2011, there were described nine additional specimens, that supported on the basis of a statistic analysis of the sternum and elements of the legs, the hypothesis that Gansus was a volant bird.