Moa were large to very large birds that lived exclusively in New Zealand. They became extinct less than 600 years ago.
They are classed as a member of the ratite group of birds, which includes the rheas (South America), ostriches (Africa and Europe–Asia), elephant birds (Madagascar), emus and cassowaries (Australia and Papua New Guinea) and kiwi (New Zealand). Ratites (from ratis, Latin for raft) are so named because their sternum (breastbone) is ‘raft-like’, or without a ‘keel’. Ratites are included in the larger group Palaeognathae (literally ‘old mouth’, due to the distinctive shape of their jaw). Palaeognaths are the sister group to all other birds, which are called neognaths. Genetic comparisons suggest that the closest relatives of moa are the flighted tinamous of South America.
Ever since moa were revealed to European scientists in 1840, the question of the bird’s closest relative has been debated. Many people assumed that it was the kiwi because the birds lived in the same area. Some researchers still believe this. However, kiwi have wings and moa did not. Others argue that moa are more closely related to emus and cassowaries.
Certainly, moa are distantly related to the other ratites and have had an independent lineage for millennia. One theory is that the moa ancestor was on the land that became New Zealand when it separated from the supercontinent Gondwana, some 85 million years ago. Another theory is that moa ancestors flew to New Zealand about 60 million years ago, long after New Zealand separated from Australia. Moa evolved to become unlike any other bird, so comparisons are difficult. They differ genetically from other ratites.
Classification of moa species
Moa were brought to the attention of Western science in 1840 by the naturalist Richard Owen, shortly after he laid eyes on a fragment of moa bone. Within eight years he had named 13 species. Their size and diversity on such a small land was heralded as a natural wonder of the world. Later, more species were accepted, so that in 1907 Walter Rothschild listed 38 in his book Extinct birds.
During the 20th century, work by researchers such as Gilbert Archey, W. R. B. Oliver and Joel Cracraft revised the number of species to be considered valid. Greater understanding of geographical variation, sexual dimorphism (where sexes differ in size), and radiocarbon dating led to the acceptance of fewer species. By 2000, 11 species in six genera were recognised, but this dropped to 10 in 2006, and nine in 2009.
Moa bones make wonderful subjects for DNA studies because in large bones the DNA is protected. Some are only a few hundred years old, and they were often collected from cold places, which preserves the DNA. A moa was one of the first extinct animals from which DNA was taken. In 2001, moa became the first extinct animals for which the entire mitochondrial genome was sequenced.
Scientists can extract ancient DNA from moa bones. They will never be able to recreate a moa, as the DNA exists in small, damaged fragments, and most is mitochondrial DNA, which only contains a tiny amount of the total moa genetic code. But analysis does allow the creation of family trees.
DNA studies and closer examination of moa skeletons have shown that just one species of giant moa (Dinornis species) lived on each of the North and South islands. They have revealed that the really large birds were females, and that the males were usually half the size – it is the most extreme example of reversed sexual dimorphism known among birds.
2013 species count
The nine moa species currently recognised are:
- two giant moa – the North Island (Dinornis novaezealandiae) and the South Island (Dinornis robustus)
- two moa with blunt bills and short legs – the eastern (Emeus crassus) and the stout-legged (Euryapteryx curtus)
- four anomalopterygine moa – little bush moa (Anomalopteryx didiformis), Mantell’s moa (Pachyornis geranoides), heavy-footed moa (Pachyornis elephantopus) and crested moa (Pachyornis australis)
- upland moa (Megalapteryx didinus).