| Adzebills | |
|---|---|
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| Skeleton ofA. otidiformis,Canterbury Museum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Gruiformes |
| Family: | †Aptornithidae Mantell, 1848 |
| Genus: | †Aptornis Owen, 1844 |
| Species | |
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| Synonyms | |
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Theadzebills,genusAptornis, were two closely relatedbirdspecies, theNorth Island adzebill, (Aptornis otidiformis), and theSouth Island adzebill, (Aptornis defossor), of theextinctfamilyAptornithidae. The family wasendemic toNew Zealand. A tentative fossil species, (Aptornis proasciarostratus), is known from theMioceneSaint Bathans fauna.[3]
Adzebills were first scientifically described in 1844 by biologistRichard Owen, who mistook them for a small species of moa.[4] The first species named wasDinornis otidiformis (laterAptornis), with the specific epithet referring to its similarity in size to thegreat bustard (Otis tarda).[5]
They have been placed in theGruiformes but this is not entirely certain. It was also proposed to ally them with theGalloanserae.[6] Studies ofmorphology andDNA sequences place them variously close to and far off from thekagu ofNew Caledonia,[7] as well as thetrumpeters.[8] However, on first discovery of fossils, they were mistaken forratites, specifically smallmoa. Its morphological closeness to the kagu may be the result ofconvergent evolution, although New Zealand's proximity toNew Caledonia and shared biological affinities (the two islands are part of the samemicrocontinent) has led some researchers to suggest they share a common ancestor fromGondwana. The Gondwanansunbittern is the closest living relative of the kagu, but these are not close to the Gruiformes proper (i.e.cranes,rails and allies).[9][10]
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A 2011 genetic study foundA. defossor to be a gruiform. There are no available DNA sequences forA. otidiformis, but it was assumed the two species were more closely related to each other than to other birds.[11]
In 2019 two studies came forth with more in-depth phylogenetic methods. The first from Boastet al. (2019) using data from near-complete mitochondrial genome sequences found adzebills to be closely related to the familySarothruridae, the flufftails.[12] Shortly after another study by Musser andCracraft (2019), using both morphological and molecular data, found support for adzebills to be closely related to trumpeters of the familyPsophiidae instead.[8] The authors took account of Boastet al. (2019) dataset and found it took 18 more steps to support the Aptornithidae-Sarothruridae clade than for Aptornithidae-Psophiidae.
The adzebills were about 80 centimetres (31 in) in length with a weight of 18 kilograms (40 lb), making them about the size of smallmoa (with which they were initially confused on their discovery) with enormous downward-curving and pointed bill, and strong legs.[13] They wereflightless and had extremely reducedwings, smaller than those of thedodo compared to the birds' overall size, and with a uniquely reducedcarpometacarpus.[14]
The two species varied mostly in size with the North Island adzebill being the smaller species; their coloration in life is not known however.
Theirfossils have been found in the drier areas of New Zealand, and only in the lowlands. Richard Owen, who described the two species, speculated that it was anomnivore, and analysis of its bones bystable isotope analysis supports this. Levels of enrichment in13C and15N for two specimens ofAptornis otidiformis compared with values for a moa,Finsch's duck andinsectivores like theowlet-nightjars suggested that the adzebill ate species higher in the food chain than insectivores.[15] They are thought to have fed on largeinvertebrates,lizards,tuatara and even smallbirds.
The adzebills were never as widespread as the moa but were subjected to the samehunting pressure as these and other large birds by the settlingMāori (and predation of eggs/hatchlings by accompanyingPolynesian rats and dogs). They became extinct before the arrival ofEuropean explorers. The Māori name forA. defossor was "ngutu hahau".[1]
