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Adzebill
Adzebill
Adzebill
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Adzebills
Temporal range: Miocene–Holocene 19–0.005 Ma
Skeleton of A. otidiformis; Canterbury Museum

Extinct (NZ TCS)[1](A. defossor)

Extinct (NZ TCS)[2](A. otidiformis)
Scientific classification Edit this 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
  • ?†Aptornis proasciarostratus
    Worthy, 2011
Synonyms

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

[edit]

Adzebills were first scientifically described by biologist Richard Owen in 1844, who mistook them for a small species of moa;[3] the type species was initially named Dinornis otidiformis with the specific epithet referring to its comparable size with the great bustard (Otis tarda; otis + formis).[4] Later on, the specimens' distinction were recognised, and so the genus Aptornis was erected to accommodate them;[5] Aptornis is noted to be a syncope of Apterygiornis, an apparent allusion to the genus Apteryx.[6] 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;[7][8] an 1997 ICZN ruling rendered it invalid and conserved Aptornis, rendering it the valid name for this taxon.[9]

The common name refers to the adze, which is a woodworking tool with the cutting edge perpendicular to the handle.[who?]

Interrelationships

[edit]

The placement of adzebills within Aves has long been contentious, with historical proposals to ally them with the Galloanserae,[10] or the kagu of New Caledonia (Rhynochetidae),[11] Its morphological resemblance to the kagu was considered to possibly be a result of convergent evolution, although New Zealand's proximity to New Caledonia (both being part of the same region of continental crust known as Zealandia, which had prehistorically been above sea level) 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.[12][13]

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.[clarification needed][14]

In 2019 two studies came forth with more in-depth phylogenetic methods. The first from Boast et al. (2019) using data from near-complete mitochondrial genome sequences found adzebills to be closely related to the family Sarothruridae, gruiform birds known as flufftails.[15] Another study by Musser and Cracraft (2019) 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. (2019) dataset and found that the Aptornithidae-Sarothruridae clade needed 18 more steps compared to Aptornithidae-Psophiidae; the latter classification is thus considered more likely (maximum parsimony).[16]

A 2025 paper recovered Nesotrochis (within the monotypic family Nesotrochidae) 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:[17]

Gruiformes

Description

[edit]
Aptornis defossor; Auckland Museum

The adzebills were about 80 centimetres (31 in) in length with a weight of 18 kilograms (40 lb), 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.[18] They were flightless, possessing extremely reduced wings with a uniquely reduced carpometacarpus; these wings were smaller proportionally than those of the dodo.[19]

The two known species varied mostly in size with the North Island adzebill being the smaller species.[citation needed] 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.[20]

Habitat and behaviour

[edit]

Their fossils 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 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 were 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.[21] They are thought to have fed on large invertebrates, lizards, tuatara and even small birds.

Extinction

[edit]

The adzebills were never as widespread as the moa but were subjected to the same hunting pressure as these and other large birds by the settling Māori (and predation of eggs/hatchlings by accompanying Polynesian rats and dogs). They became extinct before the arrival of European explorers. The Māori name for A. defossor was "ngutu hahau".[1]

Aptornis defossor skull
Restoration of A. otidiformis

References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Adzebill

View on Grokipedia
from Grokipedia
The adzebills (Aptornis spp.) were two species of large, extinct, flightless gruiform birds endemic to , characterized by their massive skulls, robust down-curved bills resembling woodworking adzes, reduced wings, and powerful legs adapted for terrestrial life. The adzebill (Aptornis otidiformis) and adzebill (Aptornis defossor) stood approximately 80 cm tall, with the latter species weighing around 18–20 kg and the former about 20% smaller at roughly 16 kg. These birds inhabited drier scrublands, grasslands, and podocarp forests across their respective islands, from up to 1000 m elevation, but were absent from wetter western coasts and subalpine zones. As opportunistic predators, adzebills used their specialized bills to probe soil and dig out prey, feeding primarily on vertebrates such as , , and small birds, as well as and possibly large earthworms; this carnivorous diet is evidenced by stones and stable nitrogen isotope analysis of bones. Their flightless nature, indicated by a reduced sternal , suggests a lifestyle as ground-dwelling hunters in predator-free ecosystems before human arrival. Both species became extinct shortly after Polynesian settlement of around 1000 years ago, likely due to hunting by early , as demonstrated by abundant bones in archaeological middens and the absence of remains in post-settlement sites. Fossils reveal that adzebills had been present in since at least the early , approximately 19 million years ago, with an ancestral species (Aptornis proasciarostratus) identified in the St Bathans Formation of . Recent genetic studies have clarified their evolutionary origins, showing that adzebills descended from African ancestors related to the small flufftails (family Sarothruridae), with a divergence estimated at 40 million years ago; their forebears likely flew from or to via a forested before the islands fully isolated. The lineage diverged from the one around 2 million years ago, possibly via a temporary between the islands.

Taxonomy and Discovery

Taxonomy

The adzebills comprise the genus Aptornis Mantell, 1848, the only genus within the extinct family Aptornithidae Bonaparte, 1856, classified in the order . This family is known exclusively from , with no living representatives. Two species are formally recognized in the : the adzebill (Aptornis otidiformis Owen, 1844) and the adzebill (Aptornis defossor Owen, 1871). The former was initially described by based on leg bones collected from Māori middens, while the latter was named from skeletal elements recovered from deposits. A potential third species, Aptornis proasciarostratus Worthy, Tennyson & Scofield, 2011, is represented by fragmentary fossils from the early St Bathans Fauna (approximately 19–16 million years old) in , suggesting an earlier diversification of the lineage. Early paleontological work by Owen led to initial confusion, as some adzebill bones were misidentified as belonging to ( spp.), with A. otidiformis first provisionally placed within that before its distinctness was established. The genus name Aptornis faced nomenclatural challenges due to a senior synonym, Apterornis Owen, , but was conserved by the in Opinion 1874 (1997), with A. otidiformis designated as the and authorship attributed to G.A. Mantell (). The vernacular name "adzebill" originates from the birds' robust, down-curved bill, which resembles the cutting edge of an adze, a woodworking tool used by Māori. The specific epithet otidiformis alludes to the bird's overall form resembling that of a bustard (Otis spp.), while defossor derives from Latin for "digger," reflecting inferred burrowing or probing foraging habits.

Discovery and Fossil Record

The adzebill was initially discovered in the 1840s by European settlers and scientists exploring , with the first bones collected from Māori kitchen middens and swamp deposits across both the North and Islands. These early finds, often unearthed during colonial surveys and interactions with local communities, provided the initial evidence of the bird's existence long after its . British anatomist described the first species of adzebill, A. otidiformis, in 1844 based on subfossil leg bones from sites, initially mistaking them for a small species of ; the genus Aptornis was established by G.A. Mantell in 1848. 's analysis, published in the Proceedings of the , established the taxonomic foundation for the species, drawing from specimens sent from . Key fossil sites for adzebill remains include on the West Coast and various localities such as Valley in , where bones are frequently preserved in swamp deposits, peat bogs, and limestone caves. These environments, characterized by waterlogged conditions, have yielded numerous subfossil elements from post-Pleistocene contexts, indicating the birds' persistence into the until shortly before European arrival. The majority of adzebill remains are subfossils—bones that are not fully mineralized due to their recent age—rather than true fossils, underscoring the species' late survival and rapid following . Complete skeletons are rare, with most collections consisting of isolated bones or partial assemblages; significant specimens, including articulated elements, are preserved at institutions such as the Museum of New Zealand Te Papa Tongarewa in .

Evolutionary Relationships

Higher Classification

The adzebills belong to the order , a diverse group encompassing cranes, rails, and their allies, and are recognized as flightless gruiforms that were endemic to since the early . They form a distinct monotypic , Aptornithidae, containing only the Aptornis, which sets them apart from other New Zealand avian endemics such as the moas of the Dinornithidae. Historically, the classification of adzebills underwent significant revisions. In 1844, described the species as Aptornis otidiformis, naming it to reflect morphological similarities to of the Otididae, initially mistaking for those of a small . By the late and into the 20th, adzebills were more commonly allied with rails of the Rallidae due to shared terrestrial adaptations, though their large size complicated direct comparisons. Morphological evidence bolsters their placement within , particularly features of the such as the with fused cristae hypotarsi and a specific configuration of the hypotarsus canals, which align with core gruiform . Cranial traits, including those of the robust , further support this affinity, distinguishing adzebills from non-gruiform lineages like moas or .

Phylogeny and Interrelationships

The phylogeny of adzebills (Aptornithidae) has been subject to ongoing debate, primarily revolving around their closest relatives within the Gruiformes order, informed by both morphological and molecular data. A 2019 morphological analysis utilizing an extensive dataset of osteological characters positioned adzebills as the sister taxon to trumpeters (Psophiidae), integrating them into core Gruiformes alongside strong support for a Kagu (Rhynochetos) + sunbittern (Eurypyga) clade. In contrast, contemporaneous molecular evidence from near-complete mitochondrial genomes recovered adzebills as sister to the Afro-Madagascan flufftails (Sarothruridae), a relationship corroborated by both maximum-likelihood and Bayesian phylogenetic analyses, though this conflicted with prior morphological hypotheses linking them to rails (Rallidae) or other Ralloidea groups. This discrepancy was addressed in a 2025 integrated study combining reanalyzed mitochondrial genomes with morphological assessments of key features like the hypotarsus, proposing the extinct cave rails (Nesotrochis spp., erected as Nesotrochidae fam. nov.) as the immediate sister taxon to adzebills, with both forming a sister to Sarothruridae within the Ralloidea. The analysis, employing BEAST for divergence dating with calibrations such as the crown at 55.6 Ma, estimated the split between Aptornithidae and Nesotrochidae at approximately 36.7 Ma (late Eocene), and their joint divergence from Sarothruridae at 42.9 Ma (mid-Eocene), resolving prior ambiguities from datasets like Oswald et al. (2021) and rejecting the Psophiidae affinity from morphological-only approaches. The African origins hypothesis for adzebills stems from the 2019 molecular phylogeny, which traces their ancestors to an ancient dispersal event from or , given the exclusively Afro-Madagascan distribution of Sarothruridae; this scenario posits overwater colonization rather than vicariance, with adzebill forebears likely rafting or flying to . Despite their co-occurrence as large flightless endemics in , no phylogenetic evidence supports a close relationship between adzebills and moas (Dinornithiformes), as the latter belong to the Paleognathae (ratites) while adzebills are firmly Neognathous gruiforms with distinct evolutionary trajectories. Divergence timelines indicate adzebill ancestors arrived in during the , approximately 25–30 million years ago, postdating the Eocene-Oligocene transition and aligning with fossil evidence from deposits (16–19 Ma).

Physical Description

Morphology

Adzebills (genus Aptornis) were flightless gruiform birds characterized by highly reduced wings and a keel-less , adaptations consistent with a fully terrestrial devoid of aerial capabilities. Their forelimbs were vestigial, with diminutive bones indicating no functional role in locomotion or other activities. In contrast, the hindlimbs were robust and pillar-like, featuring strong femurs, tibiae, fibulae, and metatarsi that supported efficient ground-based movement. The of adzebills was notably massive and thick-walled, providing structural reinforcement for the specialized feeding apparatus. The bill was long, pointed, and strongly down-curved, with a deep, laterally compressed base tapering to a sharp, hooked tip, resembling the blade of an tool and enabling powerful prying and excavation. This reinforced structure, with thick cutting edges, was adapted for foraging behaviors involving soil disturbance and manipulation of prey or resources. The postcranial skeleton further emphasized terrestrial specialization, with robust vertebrae and a sturdy that facilitated an upright posture akin to that of other flightless New Zealand avians, such as ratites. However, the cranial morphology remained distinct, marked by the exaggerated bill and reinforced cranium not seen in those relatives. Overall, these traits underscored the adzebills' evolution toward a heavily built, ground-dwelling form optimized for island environments.

Size and Variation

The adzebills (Aptornis spp.) were large flightless birds, typically standing about 80 cm tall and weighing around 18 kg. The adzebill (A. otidiformis) was slightly smaller and more gracile, with a typical body mass of approximately 16 kg, while the South Island adzebill (A. defossor) was larger and more robust, exhibiting a mean body mass of 18.9 kg (range 14.9–22.4 kg). Compared to extant gruiform birds such as rails and crakes, adzebills displayed a bulkier build, characterized by robust legs, reduced wings, and a heavily reinforced supporting the oversized bill.

Ecology

Habitat

Adzebills (genus Aptornis) were endemic to , with no evidence of populations on offshore islands beyond the mainland North and South Islands. Fossils indicate that the two recognized species occupied distinct environmental niches across the country during the Pleistocene and , prior to human arrival. Subfossil remains have been recovered from numerous sites, revealing a distribution concentrated in lowland regions rather than montane or subalpine zones. The adzebill (A. otidiformis) was primarily distributed in the drier eastern and northern lowlands, with subfossils found at scattered sites from to elevations up to 1000 m, though absent from higher subalpine grasslands. Preferred habitats included open scrublands and grasslands within a , adapted to the relatively dry conditions of the and . Evidence from sites such as and central suggests these birds thrived in unmodified landscapes before extensive forest clearance. In contrast, the South Island adzebill (A. defossor) inhabited dry podocarp forests in lowland eastern and southern areas below 1000 m, with fossils documented widely except in the wetter West Coast and arid regions. Subfossil remains are often preserved in swamps and caves such as Pyramid Valley swamp and Honeycomb Hill Cave, but the birds favored surrounding dry forest environments reflecting adaptation to temperate conditions with periodic dry phases during the Pleistocene.

Diet and Behavior

Adzebills possessed a carnivorous diet, primarily consisting of large invertebrates such as earthworms and beetle larvae, as well as vertebrates including lizards, tuatara, and possibly burrow-nesting bird chicks or eggs. This predatory feeding strategy is supported by stable nitrogen isotope (δ¹⁵N) values in bone collagen, which indicate a high trophic position comparable to or exceeding that of other New Zealand predators like the laughing owl (Sceloglaux albifacies). The small size of gizzard stones associated with adzebill remains further corroborates a non-herbivorous lifestyle focused on animal prey rather than abrasive plant material. Their foraging behavior involved using the robust, down-curved bill—adapted for prying and digging—to excavate burrows, dismantle rotting logs, and probe soil or leaf litter for hidden prey. Stable carbon isotope (δ¹³C) analyses reveal no significant marine influence in their diet, confirming a fully terrestrial foraging niche. The bill's adze-like reinforcement likely facilitated these activities, allowing efficient access to burrowing or concealed animals without reliance on speed or pursuit. As flightless birds, adzebills exhibited terrestrial locomotion characterized by a waddling supported by short, robust legs and strong tarsometatarsi, suited for stability in forested environments rather than rapid movement. There is no morphological evidence for adaptations to running or , emphasizing their role as deliberate, ground-based foragers. Little direct evidence exists for , but the absence of large gregarious assemblages in deposits suggests adzebills lived solitarily or in small units. Vocalizations remain unknown.

Extinction

Timeline

The adzebills, comprising the adzebill (Aptornis otidiformis) and adzebill (A. defossor), persisted until the late 13th to 15th centuries CE, coinciding with the arrival of Polynesian () settlers in between approximately 1250 and 1300 CE. Subfossil remains indicate possible survival into the early period, with bones found in archaeological settlements dated to the 14th century. Radiocarbon dating of subfossil bones from natural deposits and middens provides evidence of their decline. On the , the latest dates come from the Harwood site on the , where a bone yielded a calibrated age of 1268–1390 CE, though dietary marine reservoir effects could shift this to as late as 1508 CE. Earlier South Island dates include multiple specimens from Pyramid Valley in , ranging up to 1049–1154 CE. For the , remains of A. otidiformis are found in early sites, aligning with the overall extinction window by the , slightly earlier than some South Island records. The presence of adzebill bones in dated middens confirms exploitation by early until at least the , after which no further evidence appears. Adzebills were extinct prior to European contact, with no sightings recorded by explorers such as in 1769 or subsequent visitors, underscoring a pre-colonial .

Causes

The primary cause of adzebill extinction was hunting by early Māori settlers, who targeted these large flightless birds as a food source, as evidenced by the abundance of adzebill bones in archaeological middens across New Zealand dating to the late 13th to early 14th centuries CE. Secondary factors included predation and habitat disruption from introduced Polynesian mammals, particularly the Pacific rat (Rattus exulans) and Polynesian dog (Canis familiaris, or kurī), which preyed on eggs, juveniles, and adults while accelerating forest clearance through human activities. Adzebills' low reproductive rates and K-selected life history—characterized by slow maturation, few offspring, and high parental investment—rendered their populations particularly susceptible to rapid declines from these pressures, lacking the defenses evolved in predator-free ecosystems. In comparison to the moa extinctions, which involved more numerous species across diverse habitats, adzebills were less abundant overall and more restricted to forested environments, amplifying their vulnerability to localized hunting and introduced predators. There is no evidence that or late climate change played major roles in their demise, as radiocarbon analyses of pre-human remains indicate stable populations prior to Polynesian arrival around 1280 CE.

References

  1. https://www.nzbirdsonline.org.nz/species/north-island-adzebill
  2. https://www.nzbirdsonline.org.nz/species/south-island-adzebill
  3. https://otagomuseum.nz/blog/adzebill/
  4. https://set.adelaide.edu.au/news/list/2019/02/22/african-origins-of-giant-extinct-new-zealand-bird-revealed
  5. https://www.nzgeo.com/stories/the-mystery-of-the-adzebill/
  6. https://www.birdsnz.org.nz/society-publications/checklist/gruiformes-adzebills-rails-and-cranes/
  7. https://www.mdpi.com/1424-2818/11/2/24
  8. https://www.tandfonline.com/doi/abs/10.1080/03014223.1995.9517494
  9. https://www.researchgate.net/publication/331148621_Mitochondrial_Genomes_from_New_Zealand%27s_Extinct_Adzebills_Aves_Aptornithidae_Aptornis_Support_a_Sister-Taxon_Relationship_with_the_Afro-Madagascan_Sarothruridae
  10. https://collections.tepapa.govt.nz/object/338049
  11. https://doi.org/10.1206/3927.1
  12. https://paperspast.natlib.govt.nz/periodicals/TPRSNZ1891-24.2.4.1.7
  13. https://bioone.org/journals/american-museum-novitates/volume-2019/issue-3927/3927.1/A-New-Morphological-Dataset-Reveals-a-Novel-Relationship-for-the/10.1206/3927.1.full
  14. https://www.avespress.com/uploads/downloads/212/file/AS_2_8_PDFA.pdf
  15. https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.1871.tb08118.x
  16. https://www.researchgate.net/publication/315030224_Bone_stable_isotopes_indicate_a_high_trophic_position_for_New_Zealand%27s_extinct_South_Island_adzebill_Aptornis_defossor_Gruiformes_Aptornithidae
  17. https://www.gutenberg.org/cache/epub/74964/pg74964-images.html
  18. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0150871
  19. https://newzealandecology.org/nzje/3306
  20. https://www.jcu.edu.au/news/releases/2022/november/new-dates-for-mori-settlement-of-aotearoa-new-zealand
  21. https://www.birdsnz.org.nz/wp-content/uploads/2022/01/Shortnote_68_Holdaway_294-298.pdf
  22. https://teara.govt.nz/en/postage-stamp/3628/the-adzebill-aptornis
  23. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.757988/full
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