''Gansus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 seab ...

s that lived during the

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

age of the Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

(Aptian-Albian) period in what are now

Gansu Gansu is a provinces of China, province in Northwestern China. Its capital and largest city is Lanzhou, in the southeastern part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibetan Plateau, Ti ...

and

Liaoning ) , image_skyline = , image_alt = , image_caption = Clockwise: Mukden Palace in Shenyang, Xinghai Square in Dalian, Dalian coast, Yalu River at Dandong , image_map = Liaoning in China (+all claims hatched).svg , ...

provinces, western

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. 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 that includes modern birds and their very close relatives such as the ichthyornithines and the hesperornithines. This clade is defined in the ''PhyloCode'' by Juan Benito and collea ...

, the group which includes modern birds (

Neornithes Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight ...

) and extinct related groups, such as '' Ichthyornis'' and

Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic Avialae, avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genus, genera such ...

.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 Columbidae is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with small heads, relatively short necks and slender bills that in some species feature fleshy ceres. ...

and similar in appearance to

loon Loons (North American English) or divers (British English, 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 (biolog ...

s and

diving duck The diving ducks, commonly called pochards or scaups, are a category of duck which feed by diving beneath the surface of the water. They are part of Anatidae, the diverse and very large family that includes ducks, geese, and swans. The diving ...

s.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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

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.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 ''Hesperornis'' (meaning "western bird") is a genus of cormorant-like Ornithuran that spanned throughout the Campanian age, and possibly even up to the early Maastrichtian age, of the Late Cretaceous period. One of the lesser-known discoverie ...

'' (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 The Apodiformes is an Order (biology), order, or Taxonomy, taxonomic grouping, of Bird, birds which traditionally contained three living Family (biology), families—the Swift (bird), Apodidae (swifts), the Treeswift, Hemiprocnidae (treeswifts), ...

), while the pelvic limb length proportions fell within the modern birds (

), showing similarities with grebes (Podicipedidae), albatross (

Diomedeidae Albatrosses, of the biological family (biology), family Diomedeidae, are large seabirds related to the procellariidae, procellariids, storm petrels, and diving petrels in the order Procellariiformes (the tubenoses). They range widely in the So ...

) 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. The

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

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

containing all living birds plus ''Hesperornis'' and ''Ichthyornis''), ''Gansus'' is indeed the oldest known member. However, several birds from the older

Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...

and contemporary

Jiufotang Formation The Jiufotang Formation () is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. T ...

are considered ornithurans under other definitions. Under any definition, all living birds, including

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

as diverse as

ostrich Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...

es,

hummingbirds Hummingbirds are birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With approximately 366 species and 113 genus, genera, they occur from Alaska to Tierra del Fuego, but most species are found in Cen ...

and

eagle Eagle is the common name for the golden eagle, bald eagle, and other birds of prey in the family of the Accipitridae. Eagles belong to several groups of Genus, genera, some of which are closely related. True eagles comprise the genus ''Aquila ( ...

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 Euornithes Early Cretaceous dinosaurs of Asia Fossil taxa described in 1984