| Eurypygiformes | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Clade: | Eurypygimorphae |
| Order: | Eurypygiformes Hackett et al., 2008 |
| Families | |
Eurypygiformes/jʊərɪˈpɪdʒɪfɔːrmiːz/ is an order formed by the kagus, comprising two species in thefamilyRhynochetidae endemic toNew Caledonia, and thesunbittern (Eurypyga helias) from the tropical regions of theAmericas.[1] Its closest relatives appear to be the tropicbirds of the tropical Atlantic, Indian, and Pacific oceans.[2]
The affinities of Eurypygiformes are not very well resolved. The group consists of two families from aGondwanan lineage of birds. Based on some morphological characteristics, they were initially classed as members of the familyArdeidae, and later theGruiformes. 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 thePhaethontiformes.[2]The oldest known fossil eurypygiform is an indeterminate fossileurypygid from theEarly Eocene-agedGreen River Formation of the United States.[3]
When seen as a gruiform, thekagu is generally considered related to the extinctadzebills fromNew Zealand and thesunbittern fromCentral andSouth America. Recent studies do indicate that the sunbittern is the closest living relative of thekagu. For example, Fain & Houde found these to be certainlysister taxa[4] and Furoet al. indicated a close phylogenetic relationship between them bycytotaxonomy; they suggest that their common ancestor was separated by the Gondwana vicariance in South America and New Caledonia, respectively.[5] They and themesites did not group with traditional Gruiformes in their study, but instead with their proposedcladeMetaves, which also includes thehoatzin,pigeons,Caprimulgiformes,flamingos,tropicbirds,Apodiformes,sandgrouse andgrebes. The internal structure of this group was not well resolvable by their data, and contains numerous groupings not otherwise corroborated (such asCaprimulgidae andflamingos). The usefulness and monophyly of "Metaves" is therefore unclear. Notwithstanding, thekagu and sunbittern – and possibly the adzebills – seem to form a distinctGondwanan 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 possesspowder down, whereas the "core Gruiformes" do not.
While thekagu is the only living species in the family Rhynochetidae, a larger species, thelowland kagu (Rhynochetos orarius), has been described from lateHolocenesubfossil remains. The body measurements of this species were 15% greater thanRhynochetos jubatus, with no overlap in measurements except those of the wings. Given that the sites whereR. orarius has been found are all lowland sites, and that no fossils ofR. 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.[6] The validity of the species has been questioned by some authors,[7] but accepted by others.[8]
FossilMesselornithidae once included in Eurypygiformes are now considered the oldest known members ofRalloidea (Gruiformes).[9][10]
| Common name | Binomial name | Population | Status | Trend | Notes | Image |
|---|---|---|---|---|---|---|
| Kagu | Rhynochetos jubatus | 250–999[11] | EN[11] |  [11] | Total population estimated to be 601-2,000 individuals.[11] |  |
| Sunbittern | Eurypyga helias | 500,000–4,999,999[12] | LC[12] | [12] | Estimate for mature individuals only.[12] | .JPG) |
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