New Zealand once had its own species of black swan, described as having the physique of a rugby player.
Researchers from the University of Otago, Canterbury University and Te Papa have analysed ancient DNA and bone dimensions and proven the swan was a unique species. They have named it the poūwa (Cygnus sumnerensis).
Otago Palaeogentics Laboratory director Nic Rawlence, who led the study (PDF, 612KB), said the poūwa's ancestors arrived one to two million years ago from Australia.
But the bird quickly became bigger than its Australian cousins.
"The New Zealand and Chatham [Islands] black swan, which we call the poūwa, is very large, heavy compared to a small, lean Australian black swan.
"So if you think of the Australian as a soccer player then [the New Zealand bird] is Kieran Read from the All Blacks. The poūwa also had very elongated legs, proportionally short wings. You see this a lot in island eco-systems where you don't have mammalian predators, and its a sign that this bird was on the pathway to flightlessness."
Dr Rawlence said the poūwa weighed about 10kg compared with the average weight of 6kg among other black swans.
It was hunted to extinction soon after the arrival of humans in the late 13th century.
He said, prior to this study, it was thought the recolonisation of New Zealand by black swans was a unique example of replacement by the same species after extinction.
The researchers' findings have been published in biological research journal Proceedings of the Royal Society of London B.