The discovery of a toothed seabird fossil north of Christchurch is forcing scientists to rethink theories of the bird's evolution.
A fossil of a protodontopteryx, believed to have lived 62 million years ago, was found at the Waipara Greensand site in North Canterbury last year.
The petrified remains delighted amateur palaeontologist Leigh Love, who found and named the species 'protodontopteryx ruthae' after his wife Ruth, for indulging his interest in the field.
It is one of the oldest named bird species in the world, and the oldest 'bony-tooth bird', or pelagornithid, to be found south of the equator.
Canterbury Museum curator Paul Scofield said the bony, tooth-like projections on the beak turned over commonly-held views on the development of seabirds.
"Until we found this skeleton, all the really old pelagornithids had been found in the Northern Hemisphere, so everyone thought they'd evolved up there," Dr Scofield said.
Gerald Mayr, of the Frankfurt-based National History Museum, declared the find "truly amazing and unexpected".
"Not only is the fossil one of the most complete specimens of a pseudo-toothed bird, but it also shows a number of unexpected skeletal features that contribute to a better understanding of the evolution of these enigmatic birds," he said.
Scientists believe the ancient beaks were designed for catching fish, and soft- bodied prey like squids.
The bony-tooth birds would evolve to boast wingspans greater than six metres long, the length of an average modern-day elephant.
The last pelagornithid species died before modern humans evolved, around 2.5 million years ago.
The Waipara Greensand site has also yielded fossils of an ancient penguin, which stood 1.6 metres tall, and the world's oldest tropicbird fossil.
The fossils - along with the latest discovery - are being prepared to be displayed in an exhibition at the Canterbury Museum later this year.
The find was published yesterday in the journal Papers in Palaeontology.