The lowland kagu (''Rhynochetos orarius'') is a large, extinct species of

kagu The kagu or cagou (''Rhynochetos jubatus'') is a crested, long-legged, and bluish-grey bird endemic to the dense mountain forests of New Caledonia. It is the only surviving member of the genus ''Rhynochetos'' and the family Rhynochetidae, alt ...

. It was

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the island of

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 ...

Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's New Guinea in the west to Fiji in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, Va ...

in the south-west

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

region. It was described from

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 in ...

bones found at the

Pindai Caves The Pindai Caves of New Caledonia are an archaeological and palaeontological site important for the study of prehistoric human settlement as well as of the Holocene fauna of the island. The Pindai area has been occupied by humans for varying perio ...

paleontological site on the west coast of Grande Terre. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

is a right

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These sm ...

(NCP 700), held by the

Muséum national d'histoire naturelle The French National Museum of Natural History, known in French as the ' (abbreviation MNHN), is the national natural history museum of France and a ' of higher education part of Sorbonne Universities. The main museum, with four galleries, is loc ...

in Paris. The specific

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comes from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''orarius'' (of the coast) from its presumed lowland distribution, as opposed to its congener the living

''R. jubatus''.

Description

The general proportions of the various bones of the lowland kagu are very similar to those of the kagu. They differ in the greater size of the extinct species in averaging about 15% larger, with no overlap between the hindlimb elements and only rare overlap between those of the wings. The describers postulate that ''R. orarius'' and ''R. jubatus'' were lowland and highland forms, respectively.

Taxonomic uncertainty

In 2018, Jörn Theuerkauf and Roman Gula argued that ''R. orarius'' was not a valid species.Theuerkauf, J., & Gula, R. (2018). Indirect evidence for body size reduction in a flightless island bird after human colonisation. ''Journal of Ornithology'', 159(3), 823-826. They claimed that Balouet and Olson had overstated the larger size of ''R. orarius'', and assigned all their found specimens to ''R. orarius'' but none to ''R. jubatus'', which would be rare if there were two kagu species coexisting in the same island; that the extant kagu is also found in the lowlands, making speciation unlikely, and that no other two kagu species in Oceania share the same island. Instead, they proposed that there was only one kagu species in the Holocene of New Caledonia, ''R. jubatus'', which decreased in average size after human colonization as a result of hunters and introduced predators like

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

s favoring the capture of larger animals. This very same possibility had been raised by Balouet and Olson in their original paper and discounted as unlikely, but Theuerkaf and Gula pointed that similar rapid size changes have been documented in other vertebrates when exposed to new competitors and predators.

References

Extinct birds of New Caledonia Holocene extinctions Birds described in 1989 Fossil taxa described in 1989 Late Quaternary prehistoric birds Taxa named by Jean-Christophe Balouet Controversial bird taxa {{paleo-bird-stub