| Moa Temporal range: Miocene - Holocene, 17–0 Ma |
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| Restoration of an Upland Moa, Megalapteryx didinus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Superorder: | Palaeognathae |
| Order: | †Dinornithiformes Bonaparte, 1853[1] |
| Family: | †Dinornithidae Bonaparte, 1853 |
| Type species | |
| †Dinornis novaezealandiae Owen, 1843 |
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| Subgroups | |
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| Diversity | |
| 6 genera, 11 species[2] | |
| Synonyms | |
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The moa[3][4] were eleven species (in six genera)[5] of flightless birds endemic to New Zealand. The two largest species, Dinornis robustus and Dinornis novaezelandiae, reached about 3.7 m (12 ft) in height with neck outstretched, and weighed about 230 kg (510 lb).[6]
Moa are members of the ratite group in the order Dinornithiformes.[5] The eleven[5] species of moa are the only wingless birds, lacking even the vestigial wings which all other ratites have. They were the dominant herbivores in New Zealand's forest, shrubland and subalpine ecosystems for thousands of years, and until the arrival of the Māori were hunted only by the Haast's Eagle. It is generally considered that most, if not all, species of Moa died out by Maori hunting and habitat decline before European discovery and settlement.
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The kiwi were formerly regarded as the closest relatives of the moa, but comparisons of their DNA in a paper published in 2005 suggested moa were more closely related to the Australian emu and cassowary.[7] However research published in 2010 found that the moa's closest cousins were not the emu and cassowary but smaller terrestrial South American birds called the tinamous which are able to fly.[8]
Although dozens of species were described in the late 19th century and early 20th century, many were based on partial skeletons and turned out to be synonyms. Currently, eleven species are formally recognised, although recent studies using ancient DNA recovered from bones in museum collections suggest that distinct lineages exist within some of these. One factor that has caused much confusion in moa taxonomy is the intraspecific variation of bone sizes, between glacial and inter-glacial periods (see Bergmann’s rule and Allen’s rule) as well as sexual dimorphism being evident in several species. Dinornis seems to have had the most pronounced sexual dimorphism, with females being up to 150% as tall and 280% as heavy as males—so much bigger that they were formerly classified as separate species until 2003.[9][10]
Although moa were traditionally reconstructed in an upright position to create impressive height, analysis of their vertebral articulation indicates that they probably carried their heads forward,[11] in the manner of a kiwi. This would have allowed them to graze on low-level vegetation, while being able to lift their heads and browse trees when necessary.
Ancient DNA analyses have determined that there were a number of cryptic evolutionary lineages in several moa genera. These may eventually be classified as species or subspecies; Megalapteryx benhami (Archey) which is synonymised with M. didinus (Owen) because the bones of both share all essential characters. Size differences can be explained by a north-south cline combined with temporal variation such that specimens were larger during the Otiran glacial period (the last ice age in New Zealand). Similar temporal size variation is known for the North Island Pachyornis mappini.[12] Some of the other 'Large' ranges in variation for moa species can probably be explained by similar geographic and temporal factors.[13]
Sometimes, the Dinornithidae are considered to be a full order (Dinornithiformes), in which case the subfamilies listed below would be advanced to full family status (replacing "-inae" with "-idae").
Thus, the currently recognised genera and species are:[6]
Analyses of fossil moa bone assemblages [11][14][15][16][17][18][19] have provided detailed data on the habitat preferences of individual moa species, and revealed distinctive regional moa faunas:
The two main faunas identified in the South Island include: 1. The fauna of the high rainfall west coast beech (Nothofagus) forests that included Anomalopteryx didiformis and Dinornis giganteus; and 2. The fauna of the dry rainshadow forest and shrublands east of the Southern Alps that included Pachyornis elephantopus, Euryapteryx gravis, Emeus crassus and Dinornis robustus. The two other moa species that existed in the South Island; Pachyornis australis and Megalapteryx didinus might be included in a ‘subalpine fauna’, along with the widespread Dinornis robustus. P. australis is the rarest of the moa species, and the only one yet to have been found in Maori middens. Its bones have been found in caves in the northwest Nelson and Karamea districts (such as Honeycomb Hill Cave), and some sites around the Wanaka district. M. didinus is more widespread. Its name ‘upland moa’ reflects the fact its bones are commonly found in the subalpine zone. However, it also occurred down to sea level where there was suitable steep and rocky terrain (such as Punakaiki on the west coast and Central Otago).
Significantly less is known about North Island paleofaunas, due to a paucity of fossil sites compared to the South Island; however, the basic pattern of moa-habitat relationships were the same.[11] Although the South Island and the North Island shared some moa species (Euryapteryx gravis, Anomalopteryx didiformis), most were exclusive to one island, reflecting divergence over several thousand years since lower sea level had resulted in a land bridge across Cook Strait. In the North Island, Dinornis novaezealandiae and Anomalopteryx didiformis dominated in high rainfall forest habitat; a similar pattern to the South Island. The other moa species present in the North Island (Euryapteryx gravis, E. curtus, and Pachyornis geranoides) tended to inhabit drier forest and shrubland habitats. P. geranoides occurred throughout the North Island, while the distributions of E. gravis and E. curtus were almost mutually exclusive, the former having only been found in coastal sites around the southern half of the North Island.[11]
Because moa are a group of flightless birds with no vestiges of wing bones, questions have been raised about how they arrived in New Zealand, and from where. It is suggested that ancestral moa were already in New Zealand as it broke away from Antarctica 70 million years ago. Cretaceous Antarctica, as evidenced by plant fossils, was subtropical, and supported an environment lush with vegetation. Richard Dawkins suggests that Antarctica, "provided a clement and ratite-friendly land bridge linking Africa and South America on one side of the world to Australia and New Zealand on the other...".[20]
It has been long suspected that the pairs of species of moa described as Euryapteryx curtus/E. exilis, Emeus huttonii/E. crassus, and Pachyornis septentrionalis/P. mappini constituted males and females, respectively. This has been confirmed by analysis for sex-specific genetic markers of DNA extracted from bone material.[9] For example, prior to 2003 there were three species of Dinornis recognised: South Island giant moa (D. giganteus), North Island giant moa (D. novaezealandiae) and slender moa (D. struthioides). However, DNA showed that all D. struthioides were in fact males, and all D. giganteus were females. Therefore the three species of Dinornis were reclassified as two species, one each formerly occurring on New Zealand's North Island (D. novaezealandiae) and South Island (D. robustus);[9][10] robustus however, comprises three distinct genetic lineages and may eventually be classified as many species, as discussed above.
Although feeding moa were never observed by scientists, their diet has been deduced from fossilised contents of their gizzards[21][22] and coprolites,[23] as well as indirectly through morphological analysis of skull and beak, and stable isotope analysis of their bones.[11] Moa fed on a range of plant species and plant parts, including fibrous twigs and leaves taken from low trees and shrubs. The beak of Pachyornis elephantopus was analogous to a pair of secateurs, and was able to clip the fibrous leaves of New Zealand flax (Phormium tenax) and twigs up to at least 8mm in diameter.[22] Like many other birds, moa swallowed gizzard stones (gastroliths), which were retained in their muscular gizzards, providing a grinding action that allowed them to eat coarse plant material. These stones were commonly smooth, rounded quartz pebbles, but stones over 110 millimetres (4 in) in length have been found amongst preserved moa gizzard contents.[22] Dinornis gizzards could often contain several kilograms of stones.[11]
Approximately eight moa trackways, with fossilised moa footprint impressions in fluvial silts have been found throughout the North Island, including Waikanae Creek (1872), Napier (1887), Manawatu River (1895), Marton (1896), Palmerston North (1911) (see photograph to right), Ragitikei River (1939), and underwater in Lake Taupo (1973). Analysis of the spacing of these tracks indicate walking speeds of between 3 and 5 km/h (1.75–3 mph).[11]
Examination of growth rings present in moa cortical bone has revealed that these birds were K-selected, as are many other large endemic New Zealand birds.[7] They are characterised by having low fecundity and a long maturation period, taking approximately ten years to reach adult size. The large Dinornis species took the same length of time to reach adult size as small moa species, and as a result had accelerated rate of skeletal growth during their juvenile years.[7]
Fragments of moa eggshell are often encountered in archaeological sites and sand dunes around the New Zealand coast. Thirty six whole moa eggs exist in museum collections and vary greatly in size (from 120–240 millimetres (4.7–9.4 in) in length and 91–178 millimetres (3.6–7.0 in) wide).[24] The outer surface of moa eggshell is characterised by small slit-shaped pores. The eggs of most moa species were white, although those of the upland moa (Megalapteryx didinus) were blue-green. A 2010 study by Huynen et al. has found that the eggs of certain species were fragile, only around a millimeter in thickness: "Unexpectedly, several thin-shelled eggs were also shown to belong to the heaviest moa of the genera Dinornis, Euryapteryx and Emeus, making these, to our knowledge, the most fragile of all avian eggs measured to date. Moreover, sex-specific DNA recovered from the outer surfaces of eggshells belonging to species of Dinornis and Euryapteryx suggest that these very thin eggs were likely to have been incubated by the lighter males. The thin nature of the eggshells of these larger species of moa, even if incubated by the male, suggests that egg breakage in these species would have been common if the typical contact method of avian egg incubation was used."[25] Despite the bird's extinction, the high yield of DNA available from recovered fossilized eggs has allowed the moa to have its genome sequenced.[26]
There is no evidence to suggest that moa were colonial nesters. While evidence of moa nesting is often inferred from accumulations of eggshell fragments found in caves and rock shelters, little evidence exists of the nests themselves. Excavations of rock shelters in the eastern North Island during the 1940s uncovered moa nests, which were described as "small depressions obviously scratched out in the soft dry pumice".[27] Moa nesting material has also been recovered from rock shelters in the Central Otago region of the South Island, where the dry climate has resulted in the preservation of plant material used to construct the nesting platform (including twigs that have been clipped by moa bills).[28] Seeds and pollen within moa coprolites found amongst the nesting material provide evidence that the nesting season was late spring to summer.[28]
Although there is no surviving record of what sounds moa made, some idea of their calls can be gained from fossil evidence. The trachea of moa were supported by many small rings of bone known as tracheal rings. Excavation of these rings from articulated skeletons has shown that at least two moa genera (Euryapteryx and Emeus) exhibited tracheal elongation, that is, their trachea were up to 1 metre (3 ft) long and formed a large loop within the body cavity.[11] These are the only ratites known to exhibit this feature, which is also present in several other bird groups including swans, cranes and guinea fowl. The feature is associated with deep, resonant vocalisations that can travel long distances.
Several remarkable examples of moa remains have been found that exhibit soft tissues (muscle, skin, feathers), preserved through desiccation when the bird died in a naturally dry site (for example, a cave with a constant dry breeze blowing through it). Most of these specimens have been found in the semi-arid Central Otago region, the driest part of New Zealand. These include:
Two specimens are known from outside the Central Otago region:
In addition to these specimens, loose moa feathers have been collected from caves and rockshelters in the southern South Island, and so some idea of the moa plumage can be gained. The preserved leg of Megalapteryx didinus from the Old Man Range reveals that this species was feathered right down to the foot. This is likely to have been an adaptation to living in high altitude snowy environments, and is also seen in the Darwin’s Rhea which lives in a similar seasonally snowy habitat.[11] Moa feathers are up to 23 centimetres (9 in) long and a range of colours have been reported, including reddish brown, white, yellowish and purplish.[11] Dark feathers with white or creamy tips have also been found, and indicate that some moa species may have had plumage with a speckled appearance.
The moa's only predator was the massive Haast's Eagle—until the arrival of human settlers.
The Māori arrived sometime before A.D. 1300, and all moa genera were soon driven to extinction by hunting and, to a lesser extent, forest clearance. By about A.D. 1400 almost all moa are generally thought to have become extinct, along with the Haast's Eagle which had relied on them for food. Recent research using carbon-14 dating of middens strongly suggests that this took less than a hundred years,[37] rather than the period of exploitation lasting several hundred years which had been earlier believed.
Some authors have speculated that a few Megalapteryx didinus may have persisted in remote corners of New Zealand until the 18th and even 19th centuries, but the view is not widely accepted.[32] Some Māori hunters claimed to be in pursuit of the moa as late as the 1770s. Whalers and sealers recalled seeing monstrous birds along the coast of the South Island, and in the 1820s a man named George Pauley made an unverified claim of seeing a moa in the Otago Region of New Zealand.[38][39] An expedition in the 1850s under Lieutenant A. Impey reported two Emu-like birds on a hillside, on the South Island, and an 1861 story from the Nelson Examiner told of three-toed footprints measuring 36 centimetres (14 in) between Takaka and Riwaka, found by a surveying party, and finally in 1878 the Otago Witness published an account from a farmer and his shepherd.[39]
Joel Polack, a trader who lived on the East Coast of the North Island from 1834 to 1837, records in 1838 that he had been shown 'several large fossil ossifications' found near Mt Hikurangi. He was certain that these were the bones of a species of emu or ostrich, noting that 'the Natives add that in times long past they received the traditions that very large birds had existed, but the scarcity of animal food, as well as the easy method of entrapping them, has caused their extermination'. Polack further noted that he had received reports from Māori that a 'species of Struthio' still existed in remote parts of the South Island.[40][41] Dieffenbach[42] also refers to a fossil from the area near Mt Hikurangi, and surmises that it belongs to 'a bird, now extinct, called Moa (or Movie) by the natives'. In 1839, John W. Harris, a Poverty Bay flax trader who was a natural history enthusiast, was given a piece of unusual bone by a Māori who had found it in a river bank. He showed the 15 centimetres (6 in) fragment of bone to his uncle, John Rule, a Sydney surgeon, who sent it to Richard Owen who at that time was working at the Hunterian Museum at the Royal College of Surgeons in London.[39] Owen became a noted biologist, anatomist and paleontologist at the British Museum.
Owen puzzled over the fragment for almost four years. He established it was part of the femur of a big animal, but it was uncharacteristically light and honeycombed. Owen announced to a skeptical scientific community and the world that it was from a giant extinct bird like an ostrich, and named it Dinornis. His deduction was ridiculed in some quarters, but was proved correct with the subsequent discoveries of considerable quantities of moa bones throughout the country, sufficient to reconstruct skeletons of the birds.[39]
In July 2004, the Natural History Museum in London placed on display the moa bone fragment Owen had first examined, to celebrate 200 years since his birth, and in memory of Owen as founder of the museum.
Since the discovery of the first moa bones in the late 1830s, thousands more have been found. They occur in a range of late Quaternary and Holocene sedimentary deposits, but are most common in three main types of site:
Bones are commonly found in Caves or ‘tomo’ (Maori word for doline or sinkhole; often used to refer to pitfalls or vertical cave shafts). The two main ways that the moa bones were deposited in such sites were: 1. Birds that entered the cave to nest or escape bad weather, and subsequently died in the cave; and 2. Birds that fell into a vertical shaft and were unable to escape. Moa bones (and the bones of other extinct birds) have been found in caves throughout New Zealand, especially in the limestone/marble areas of northwest Nelson, Karamea, Waitomo and Te Anau.
Moa bones and eggshell fragments sometimes occur in active coastal sand dunes, where they may erode from paleosols and concentrate in ‘blowouts’ between dune ridges. Many such moa bones predate human settlement, although some can originate from Maori midden sites which frequently occur in dunes near harbours and river mouths (for example the large moa hunter sites at Shag River, Otago and Wairau Bar, Marlborough).
Densely intermingled moa bones have been encountered in swamps throughout New Zealand. The most well-known example is at Pyramid Valley in north Canterbury,[43] where bones from at least 183 individual moa have been excavated. Many explanations were proposed to account for how these deposits had formed, ranging from poisonous spring waters to floods and wildfires. However the currently accepted explanation is that the bones accumulated at a slow rate over thousands of years, from birds that had entered the swamps to feed and became trapped in the soft sediment.[44]
The moa is thought to be extinct, but there has been occasional speculation—since at least the late 19th century,[45][46] and as recently as 1993[47][48][49] and 2008[50]—that some moa may still exist, particularly in the rugged wilderness of South Westland and Fiordland. Cryptozoologists and others reputedly continue to search for them,[51] but their claims and supporting evidence (such as of purported footprints[50] or blurry photos) have earned little attention from mainstream experts, and are widely considered pseudoscientific.[32]
The rediscovery of the takahē in 1948 after none had been seen since 1898 showed that rare birds may exist undiscovered for a long time. However, the takahē is a much smaller bird than the moa, and was rediscovered after its tracks were identified—yet no reliable evidence of moa tracks has ever been found, and experts still contend that moa survival is extremely unlikely, since this would involve the ground-dwelling birds living unnoticed for over five-hundred years in a region visited often by hunters and hikers.[50]