Adzebill
The adzebills are two species of gruiform birds belonging to the genus Aptornis, the sole member of the extinct family Aptornithidae, which were endemic to New Zealand. The species were divided between the North and South islands of the country, with Aptornis otidiformis being the North Island adzebill, and Aptornis defossor being the South Island adzebill. Additional material from the Saint [Bathans fauna] may represent a third species.
Taxonomy
Adzebills were first scientifically described by biologist Richard Owen in 1844, who mistook them for a small species of moa; the type species was initially named Dinornis otidiformis with the specific epithet referring to its comparable size with the great bustard. Later on, the specimens' distinction were recognised, and so the genus Aptornis was erected to accommodate them; Aptornis is noted to be a syncope of Apterygiornis, an apparent allusion to the genus Apteryx. The alternate spelling Apterornis was coined a week earlier, though it was considered a likely typographical error and was not coined by nor ever used by Owen; a 1997 ICZN ruling rendered it invalid and conserved Aptornis, rendering it the valid name for this taxon.The common name refers to the adze, which is a woodworking tool with the cutting edge perpendicular to the handle.
Interrelationships
The placement of adzebills within Aves has long been contentious, with historical proposals to ally them with the Galloanserae, or the kagu of New Caledonia, Its morphological resemblance to the kagu was considered to possibly be a result of convergent evolution, although New Zealand's proximity to New Caledonia has led some researchers to suggest the two shared a common ancestor which lived in prehistoric Gondwana; another Gondwanan bird, the sunbittern of South America, is the closest living relative of the kagu.A 2011 genetic study recovered A. defossor as a gruiform, a lineage of birds which includes the cranes, coots, and moorhens. At the time, there were no available DNA sequences for A. otidiformis, but it was assumed the two species were more closely related to each other than to other birds.
In 2019 two studies came forth with more in-depth phylogenetic methods. The first from Boast et al. using data from near-complete mitochondrial genome sequences found adzebills to be closely related to the family Sarothruridae, gruiform birds known as flufftails. Another study by Musser and Cracraft was published shortly afterwards, using both morphological and molecular data, found support for adzebills to be closely related to trumpeters of the family Psophiidae instead; these authors took account of Boast et al. dataset and found that the Aptornithidae-Sarothruridae clade needed 18 more steps compared to Aptornithidae-Psophiidae; the latter classification is thus considered more likely.
A 2025 paper recovered Nesotrochis to be the sister taxon of the adzebill family. Below is the result of their phylogenetic analysis, using the BEAST program to analyze 9,615 base pairs of mitochondrial DNA:
Description
The adzebills were about in length with a weight of, making them about the size of small moa with enormous downward-curving and pointed bill, and strong legs. They were flightless, possessing extremely reduced wings with a uniquely reduced carpometacarpus; these wings were smaller proportionally than those of the dodo.The two known species varied mostly in size with the North Island adzebill being the smaller species. Unlike moas, which in some species preserved soft tissue, the life appearance of Aptornis, such as coloration or feather types, is not directly known.
Fossils of a "very similar" species is known from the Miocene-epoch Saint Bathans fauna, being given the name ?Aptornis proasciarostratus; due to the fragmentary condition of the specimens, the describers deemed it possible that this animal belongs to another genus within Aptornithidae, thus the provisional nature of its placement in Aptornis.