Adzebill

Adzebills
File:Aptornis.jpg
Skeleton of A. otidiformis, Canterbury Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Gruiformes
Family:	†Aptornithidae Mantell, 1848
Genus:	†Aptornis Owen, 1844
Species
†Aptornis otidiformis Owen, 1844 †Aptornis defossor Owen, 1871
Synonyms
Apterornis Dinornis otidiformis

The adzebills, genus Aptornis, were two closely related bird species, the North Island adzebill, Aptornis otidiformis, and the South Island adzebill, Aptornis defossor, of the extinct family Aptornithidae. The family was endemic to New Zealand.

Taxonomy

File:Aptornis cranium.jpg

A. defossor skull drawn by James Erxleben

They have been placed in the Gruiformes but this is not entirely certain. It was also proposed to ally them with the Galloanserae (Weber & Hesse, 1995). Studies of morphology and DNA sequences place them variously close to and far off from the kagu of New Caledonia, as well as the trumpeters; however, on first discovery of fossils, they were mistaken for ratites, specifically small moa. Its morphological closeness to the kagu may be the result of convergent evolution, although New Zealand's proximity to New Caledonia and shared biological affinities (the two islands are part of the same microcontinent) has led some researchers to suggest they share a common ancestor from Gondwana. If so, it is interesting to note that the Gondwanan sunbittern is most likely the closest living relative of the kagu, and these two may also be reasonably close to the mesites, yet other "odd gruiforms" from the Southern Hemisphere, but do not seem to be close to the Gruiformes proper (i.e. cranes, rails and allies. See e.g. Fain & Houde, 2004). On the other hand, should the adzebills be closer to the trumpeters, placement in the Gruiformes is likely to be correct even if the kagu and sunbittern are split off.

A 2011 genetic study found A. defossor to be a Gruiform. There are 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.

Description

In life the adzebills were massive gruiforms, about 80 cm in length with a weight of 18 kg, making them about the size of small moa (with which they were initially confused on their discovery) with enormous downward-curving and pointed bill, and strong legs. They were flightless and had extremely reduced wings, smaller than those of the dodo compared to the birds' overall size, and with a uniquely reduced carpometacarpus (Livezey, 1994).

The two species varied mostly in size with the North Island adzebill being the smaller species; their coloration in life is not known however.

Habitat and behaviour

File:Aptornis BW.jpg

Restoration

Their fossils have been found the drier areas of New Zealand, and only in the lowlands. Richard Owen, who described the two species, speculated that it was an omnivore, and analysis of its bones by stable isotope analysis supports this. Levels of enrichment in ¹³C and ¹⁵N for two specimens of Aptornis otidiformis compared with values for a moa, Finsch's duck and insectivores like the owlet-nightjars suggested that the adzebill ate species higher in the food chain than insectivores. They are thought to have fed on large invertebrates, lizards, tuataras and even small birds.

Extinction

The adzebills were never as widespread as the moa, but subjected to the same hunting pressure as these and other large birds by the settling Polynesians (and predation of eggs/hatchlings by accompanying kiore and dogs). They became extinct before the arrival of European explorers.

References

• Fain, Matthew G. & Houde, Peter (2004): Parallel radiations in the primary clades of birds. Evolution 58(11): 2558-2573. doi:10.1554/04-235 PMID 15612298 PDF fulltext
• Livezey, Bradley C. (1994): The carpometacarpus of Apterornis. Notornis 41(1): 51–60. PDF fulltext
• Weber, Erich & Hesse, Angelika (1995): The systematic position of Aptornis, a flightless bird from New Zealand. Courier Forschungsinstitut Senckenberg 181: 292-301.
• Worthy, Trevor H. (1989): The glossohyal and thyroid bone of Aptornis otidiformes. Notornis 36(3): 248 PDF fulltext
• Worthy, Trevor H., & Holdaway, Richard N. (2002) The Lost World of the Moa, Indiana University Press:Bloomington, ISBN 0-253-34034-9
• North Island Adzebill. Aptornis otidiformis. by Paul Martinson. Artwork produced for the book Extinct Birds of New Zealand, by Alan Tennyson, Te Papa Press, Wellington, 2006
• South Island Adzebill. Aptornis defossor. by Paul Martinson. Artwork produced for the book Extinct Birds of New Zealand, by Alan Tennyson, Te Papa Press, Wellington, 2006
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