Eurypygiformes is an order formed by the kagus, comprising two species in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Rhynochetidae endemic to

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

, and the sunbittern (''Eurypyga helias'') from the tropical regions of the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...

. Its closest relatives appear to be the tropicbirds of the tropical Atlantic, Indian, and Pacific oceans.

Classification

The affinities of Eurypygiformes are not very well resolved. The group consists of two families from a

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

n lineage of birds. Based on some morphological characteristics, they were initially classed as members of the family Ardeidae, and later the Gruiformes. According to Jarvis, et al.'s 2014 "Whole-genome analyses resolve early branches in the tree of life of modern birds", the group is distantly related to the Phaethontiformes.Whole-genome analyses resolve early branches in the tree of life of modern birds
Erich D. Jarvis, ''et al''., ''Science'' 12 December 2014: Vol. 346 no. 6215 pp. 1320-1331 DOI: 10.1126/science.1253451 When seen as a gruiform, the kagu is generally considered related to the extinct adzebills from

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...

and the sunbittern from

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and

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. Recent studies do indicate that the sunbittern is the closest living relative of the kagu. For example, Fain & Houde found these to be certainly sister taxa and Furo ''et al.'' indicated a close phylogenetic relationship between them by cytotaxonomy; they suggest that their common ancestor was separated by the Gondwana vicariance in South America and New Caledonia, respectively. They and the

mesite The mesites (Mesitornithidae) are a family of birds that are part of a clade (Columbimorphae) that include Columbiformes and Pterocliformes. They are smallish flightless or near flightless birds endemic to Madagascar. They are the only family wit ...

s did not group with traditional Gruiformes in their study, but instead with their proposed

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 ter ...

Metaves, which also includes the hoatzin, pigeons, Caprimulgiformes, flamingos, tropicbirds, Apodiformes,

sandgrouse Sandgrouse is the common name for Pteroclidae , a family of sixteen species of bird, members of the order Pterocliformes . They are traditionally placed in two genera. The two central Asian species are classified as ''Syrrhaptes'' and the oth ...

and

grebes Grebes () are aquatic diving birds in the order Podicipediformes . Grebes are widely distributed freshwater birds, with some species also found in marine habitats during migration and winter. Some flightless species exist as well, most notably i ...

. The internal structure of this group was not well resolvable by their data, and contains numerous groupings not otherwise corroborated (such as Caprimulgidae and flamingos). The usefulness and monophyly of "Metaves" is therefore unclear. Notwithstanding, the kagu and sunbittern – and possibly the adzebills – seem to form a distinct

n lineage of birds, possibly one order, possibly more, even though the relationships between them, the mesites, and the "core Gruiformes" are not yet resolved. It is notable, however, that the sunbittern and the mesites possess powder down, whereas the "core Gruiformes" do not. While the kagu is the only living species in the family Rhynochetidae, a larger species, the lowland kagu (''Rhynochetos orarius''), has been described from late

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

subfossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains. The body measurements of this species were 15% greater than '' Rhynochetos jubatus'', with no overlap in measurements except those of the wings. Given that the sites where ''R. orarius'' has been found are all lowland sites, and that no fossils of ''R. jubatus'' were found in these sites, the scientists who described the fossils suggested they represented highland and lowland species, respectively. ''R. orarius'' is one of many species to have become extinct in New Caledonia after the arrival of humans. The validity of the species has been questioned by some authors,del Hoyo, J. Elliott, A. & Sargatal, J. (editors). (1996) ''Handbook of the Birds of the World. Volume 3: Hoatzin to Auks''. Lynx Edicions. but accepted by others. Fossil Messelornithidae once included in Eurypygiformes are now considered the oldest known members of Ralloidea ( Gruiformes).

References

{{Taxonbar, from=Q147907 Neognathae Bird orders