''Gansus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

aquatic bird A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabi ...

s that lived during the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

age of the Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

(Aptian-Albian) period in what are now

Gansu Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibet ...

and

Liaoning Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...

provinces, western

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. The rock layers from which their fossils have been recovered are dated to 120 million years ago.Ji, S.-A. Atterholt, J. O'Connor, J.K. Lamanna, M.C. Harris, J.D. Li, D.-Q. You, H.-L. & Dodson, P. (2011
A new, three-dimensionally preserved enantiornithine bird (Aves: Ornithothoraces) from Gansu Province, north-western China
''Zoological Journal of the Linnean Society'' 162(1):201–219. It was first described in 1984 on the basis of an isolated left leg.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. It is the oldest-known member of the

Ornithurae Ornithurae (meaning "bird tails" in Greek) is a natural group which includes the common ancestor of ''Ichthyornis'', ''Hesperornis'', and all modern birds as well as all other descendants of that common ancestor. Classification Ernst Haeckel coi ...

, the group which includes modern birds ( Neornithes) and extinct related groups, such as '' Ichthyornis'' and Hesperornithes.O’Connor, J.K & Zhou, Z. (2012
A redescription of ''Chaoyangia beishanensis'' (Aves) and a comprehensive phylogeny of Mesozoic birds
''Journal of Systematic Palaeontology''.

Description

The genus ''Gansus'' contains a single species, ''G. yumenensis'', which was about the size of a pigeon and similar in appearance to

loon Loons (North American English) or divers (British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family Gaviidae and order Gavi ...

s and diving ducks.You, H.-L. Lamanna, M.C. Harris, J.D. Chiappe, L.M. O'Connor, J.K. Ji, S.-A. Lu, J.-C. Yuan, C.-X. Li, D.-G. Zhang, X. Lacovara, K.J. Dodson, P. & Ji, Q. (2006
A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China
''Science'' 312:1640-1643. It had many features common among modern birds, and also retained some basal 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 Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

at the site of an ancient lake at Changma, Gansu; the geological stratum in which the fossils were found is the

Xiagou Formation The Xiagou Formation is the middle strata of the Xinminbao Group. It is named for its type site in Xiagou, in the Changma Basin of Gansu Province, northwestern China and is considered Early Cretaceous in age. It is known outside the specialized ...

. 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.Li, Y. Zhang, Y.-G. Zhou, Z.-H. Li, Z.-H. Liu, D. & Wang, X.-L. (2011) New material of ''Gansus'' and a discussion on its habit. ''Vert. PalAs'' 49:435–445. You ''et al.'' (2006) concluded that the anatomical characteristics of ''Gansus'' were similar to foot-propelled diving birds, such as '' Hesperornis'' (from the

) and the loons ( Gaviidae) and grebes ( Podicipedidae). On the other hand, Li ''et al.'' (2011) concluded that ''Gansus'' showed a more similar morphology to ducks. Two years later, Nudds ''et al.'' (2013) showed that the pectoral limb length proportions of ''Gansus'' were most similar to swifts and hummingbirds ( Apodiformes), while the pelvic limb length proportions fell within the modern birds ( Neornithes), showing similarities with grebes (Podicipedidae), albatross ( Diomedeidae) and cormorants ( Phalacrocoracidae), suggesting that ''Gansus'' was both volant and capable of diving to some degree using either foot-propelled or, perhaps, both its wings and its feet for underwater locomotion.Nudds, R.L, Atterholt, J. Wang, X. You, H.-L. & Dyke, G.J. (2013
Locomotory abilities and habitat of the Cretaceous bird ''Gansus yumenensis'' inferred from limb length proportions
''Journal of Evolutionary Biology'' 26(1):150–154.

Classification

''Gansus'' was described as the oldest known

ornithuran Ornithurae (meaning "bird tails" in Greek) is a natural group which includes the common ancestor of ''Ichthyornis'', ''Hesperornis'', and all modern birds as well as all other descendants of that common ancestor. Classification Ernst Haeckel co ...

. The

, however, has been given several very different definitions. In the definition used by You and colleagues (that is, the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

containing all living birds plus ''Hesperornis'' and ''Ichthyornis''), ''Gansus'' is indeed the oldest known member. However, several birds from the older Yixian Formation and contemporary Jiufotang Formation are considered ornithurans under other definitions. Under any definition, all living birds, including taxa as diverse as

ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...

es, hummingbirds and

eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...

s, are descended from basal ornithurans, many of which were semi-aquatic. It is now thought possible that all modern 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. This hypothesis was corroborated by later phylogenetic studies that included this taxon.O'Connor, J.K., Gao, K.-Q. & Chiappe, L.M. (2010) A new ornithuromorph. (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher− level diversity. ''Journal of Vertebrate Paleontology'' 30:311–321.

References

External links

Waterfowl fossils fill in a big missing link.
{{Taxonbar, from=Q2130568 Prehistoric euornitheans Early Cretaceous birds of Asia Bird genera Fossil taxa described in 1984