Oxyurinae
Encyclopedia
Oxyurinae is a subfamily of the duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

, goose
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

 and swan
Swan
Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae...

 family of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, Anatidae
Anatidae
Anatidae is the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups...

. It has been subject of considerable debate about its validity and circumscription. Most of its members have long stiff tail feathers which are erected when the bird is at rest, and relatively large swollen bills. Though their relationships are still enigmatic, they appear to be closer to swans and true geese rather than to the typical ducks. The highest diversity is found in the warmer parts of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, but at least one species occurs in a major part of the world.

Their habitus
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 resembles a freshwater diving duck
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 the diverse and very large Anatidae family that includes ducks, geese, and swans....

, particularly when moving on dry land. Their legs are set far back, making them awkward walkers, so they rarely leave the water. When at rest, the tails are a notable difference as per above, and in the water they often swim very deep-set. Their unusual courtship displays involve drumming noises from inflatable throat-sacs, head throwing, and erecting short crests. Most display singly with a very elaborate and peculiar display, but Musk Duck
Musk Duck
The Musk Duck is a highly aquatic, stiff-tailed duck native to southern Australia. It is the only living member of the genus Biziura. An extinct relative, the New Zealand Musk Duck or de Lautour's Duck , once occurred on New Zealand, but is only known from prehistoric subfossil bones...

s congregate at leks and have a more limited display.

Systematics

There is one mid-sized genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 and two or three which are monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...

 today:
  • Heteronetta
    Black-headed Duck
    The Black-headed Duck is a South American duck allied to the stiff-tailed ducks in the subfamily Oxyurinae of the family Anatidae. It is the only member of the genus Heteronetta....

  • Nomonyx
    Masked Duck
    The Masked Duck is a tiny stiff-tailed duck ranging through the tropical Americas. They are found from Mexico to South America and also in the Caribbean...

  • Oxyura
  • Biziura
    Musk Duck
    The Musk Duck is a highly aquatic, stiff-tailed duck native to southern Australia. It is the only living member of the genus Biziura. An extinct relative, the New Zealand Musk Duck or de Lautour's Duck , once occurred on New Zealand, but is only known from prehistoric subfossil bones...

    (tentatively placed here)


The Black-headed Duck
Black-headed Duck
The Black-headed Duck is a South American duck allied to the stiff-tailed ducks in the subfamily Oxyurinae of the family Anatidae. It is the only member of the genus Heteronetta....

 of Heteronetta is indisputably quite basal, looking more like a typical ducklike Anatidae
Anatidae
Anatidae is the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups...

 with a short tail and normal bill. The Masked Duck
Masked Duck
The Masked Duck is a tiny stiff-tailed duck ranging through the tropical Americas. They are found from Mexico to South America and also in the Caribbean...

 of Nomonyx has a more intermediate position; it probably diverged from the lineage leading to the main radiation some time after Heteronetta.

The musk ducks (Biziura
Biziura
Biziura is a genus of stiff-tailed ducks endemic to Australasia and containing one living and one fossil species.-Species:* B. lobata Stephens, 1824 – Musk Duck – Widely distributed through south-eastern Australia, south-west Western Australia and the Murray-Darling Basin.* B...

) are noted for their bizarre habitus
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 and pronounced sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

; they are of uncertain position and decidedly aberrant. Their anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

 is more similar to Oxyura than to the two less derived genera, but still unique in many respects. mtDNA cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...

 sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

 data suggests a closer relationship with the pink-eared ducks (Malacorhynchus) which if correct would represent one of the most drastic cases of divergent adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

 in the whole Anseriformes
Anseriformes
The order Anseriformes contains about 150 living species of birds in three extant families: the Anhimidae , Anseranatidae , and the Anatidae, which includes over 140 species of waterfowl, among them the ducks, geese, and swans.All species in the order are highly adapted for an aquatic existence at...

.

Altogether however, the only thing that seems clear is that the musk ducks probably are not part of the stiff-tailed ducks in the strict sense but rather represent a not-too-distantly related lineage that is highly convergent
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 as regards their hindlimb anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

. These two are probably part of a very ancient radiation of Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

n (often Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n) waterfowl, including such forms as the Cape Barren Goose
Cape Barren Goose
The Cape Barren Goose is a large goose resident in southern Australia. The species is named for Cape Barren Island, where specimens were first sighted by European explorers.-Taxonomy:...

 (Cereopsis), the Coscoroba Swan
Coscoroba Swan
The Coscoroba Swan is a species of waterfowl inhabiting southern South America. It is the smallest of the birds called "swans", but still a large species of waterfowl, averaging 4.2 kg , 1 m long and 1.57 m across the wings...

 (Coscoroba), the Freckled Duck
Freckled Duck
The Freckled Duck is a moderately large, broad-bodied duck native to southern Australia. The duck is protected by law...

 (Stictonetta) which once was placed in the Oxyurinae, or the pygmy geese (Nettapus). But the exact relationships between these lineages remains unresolved. For example, the Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

n White-backed Duck
White-backed Duck
The White-backed Duck is a waterbird of the family Anatidae. It is distinct from all other ducks, but most closely related to the whistling ducks in the subfamily Dendrocygninae, though also showing some similarities to the stiff-tailed ducks in the subfamily Oxyurinae...

 (Thalassornis) also shows some similarities to Oxyura, but again, this may be yet another case of convergent evolution.

There is one fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 genus of Oxyurinae, Tirarinetta from the Pliocene of Australia, and some prehistoric members of genera still extant. Three enigmatic genera of waterfowl, Mionetta from the Late Oligocene to Middle Miocene
Middle Miocene
The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene....

 of central Europe and Dunstanetta and Manuherikia
Manuherikia
Manuherikia was a parliamentary electorate in the Otago Region of New Zealand. It existed from 1866 to 1870 and was represented by two Members of Parliament.-Population centres:The electorate included the towns of Alexandra, Cromwell, Ranfurly and Roxburgh....

from the Bathans Early/Middle Miocene of Otago, New Zealand, show some similarities to oxyurine ducks and judging from biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

, the latter two may plausibly be related. On the other hand, Manuherikia and Mionetta are sometimes held to be Dendrocheninae adapted to diving and therefore closer to whistling-ducks, a very ancient lineage of Anatidae.
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