NZ kiwi made in Australia?
New fossils suggest the kiwi bird evolved from an Australian ancestor.
RESEARCHERS HAVE FOUND evidence that the kiwi, a national symbol of New Zealand, descended from a tiny Australian bird that flew across the ditch some 40 million years ago.
Australian and NZ researchers behind the find analysed two fossils of a 20-million-year-old kiwi species (Proapteryx micromeros) recently found near Otago, on the South Island. Their findings were published this month in the Proceedings of the 8th International Meeting of the Society of Avian Palaeontology and Evolution.
The fossils reveal that early kiwis were small birds that could probably fly. Recent genetic studies suggest they share a common ancestor with the emu and cassowary of Australia.
Kiwi fossil record
“This discovery reveals a fossil record for kiwis,” says lead researcher Dr Trevor Worthy at Flinders University in South Australia. “The fossils support the idea that about 40 million years ago, a small flying ancestor was in Australia and a group of them flew to New Zealand and thereafter evolved into the kiwi,” he says. Others that remained behind became the emu and the cassowary.
The new study disproves a commonly held theory that chicken-sized modern kiwis, descended from the extinct moa, a giant wingless bird. This theory was championed by evolutionary biologist Stephen Gould in the 1980s.
“Gould’s theory arose because of the extraordinarily large size of kiwi eggs,” Trevor says. In relation to its body size, the kiwi lays larger eggs than any other bird. “Basically, to explain this large egg, Gould suggested kiwi ancestors were large moa-like birds and that through time the birds shrank but retained the large egg.”
Kiwi built for flight
Trevor’s team instead argue that the kiwi’s ancestor was just a third of the size of the smallest living kiwi species. “Therefore the evolutionary trajectory of kiwis over the last 20 million years has been towards larger size and towards a totally terrestrial lifestyle,” he told Australian Geographic.
“Although the thigh bone we found was undoubtedly from a kiwi, it was much smaller and more slender than what we were expecting.” says study co-author Professor Steve Salisbury. “With longer legs and a shorter bill, it seems likely that this bird was a better flier than any living kiwi, making overwater dispersal from Australia a real possibility.”
Steve says it is likely that the evolutionary split between kiwi, cassowaries and emus would have occurred as many as 40 million years ago and that flying kiwi were once residents of Australia. “As yet, no fossil have turned up, but that might be because we haven’t recognised them,” he says.
Dr Walter Boles, an ornithologist at the Australian Museum in Sydney, says the finding is a major insight: “Because of the kiwi’s significance in the larger picture of avian evolution, this finding makes an important contribution to our understanding of how these birds developed, both by themselves and as part of the larger investigation of New Zealand’s ancient avian fauna.”