New Zealand once had its own species of black swan but, like the moa, it was hunted to extinction soon after humans arrived in the late 13th century, a study has found.
The swan, pouwa or Cygnus sumnerensis, was later replaced by its Australian cousin, Cygnus atratus, now common around New Zealand.
Previously it was thought the two were the same species.
But researchers from Otago University, Canterbury Museum and Te Papa, analysing ancient DNA and bone dimensions, say there is proof that pouwa was a unique species.
Lead author Nic Rawlence compared the difference in build between the two birds to that between a rugby and a soccer player pouwa were much heavier and larger.
They were also on the way to being flightless when they became extinct.
Dr Rawlence said the findings, published in the Proceedings of the Royal Society, are one of a growing number of examples of extinction and colonisation since the arrival of humans in New Zealand.
Australian black swans first got to New Zealand about one to two million years ago, during the Pleistocene Ice Age.
On settling, they rapidly became bigger than their Australian cousins, developing elongated legs and becoming more terrestrial in habitat.
Dr Rawlence said that, until the mid-1990s, scientists thought that the black swans in New Zealand when Polynesians arrived were the same as the Australian ones here now.
However, the first Europeans in the late 18th century saw no black swans, but they found their bones in pre-human fossil sites and archaeological deposits.
In the 1860s, Australian black swans were introduced from Victoria and their population grew and spread within three or four years. NZN