The discovery of three small bones near St Bathans in Central Otago is set to rewrite the textbooks on New Zealand evolution.
A team led by palaeontologist Trevor Worthy and Te Papa fossil curator Alan Tennyson discovered the remains of what is a primitive land mammal five years ago.
The creature, believed to be about the size of a mouse, was between 16 to 19 million years old.
The fossils, which were sent to Australia for further analysis, were found in layers of sediment in a site near St Bathans Loop Rd.
Mr Tennyson said the mammal might not be big in size but it was one of the most important fossil finds in New Zealand's history.
"This ranks up there with the discovery of the first moa bones, the first dinosaur bones in New Zealand," he said.
"It will really lead to the rewriting of textbooks. New Zealand may not have grown like we first thought."
What has the scientists so excited is the age of the creature and the very fact it is a mammal.
The area where it was discovered was swamp-like millions of year ago and is called Lake Manuherikia by scientists after the river that now runs through part of Central Otago.
The lake also carried creatures such as crocodiles and vegetation such as gum trees.
Mr Tennyson said Lake Manuherikia went from where the Waitaki River was now, down to Southland.
Previously, New Zealand had been seen as a land of birds, with the only known native land mammal being the bat, which had an unknown history.
Birds were seen as thriving and creatures such as giant eagles filled the void left by the lack of mammals.
But the discovery of this mammal, dated from 16 to 19 million years ago, showed mammals did exist at least from 82 million years ago when New Zealand broke away from the Gondwana land mass.
"That shows the land of birds is not true," Mr Tennyson said.
"However, if land mammals were this size, then the story may not have changed much. Birds would have been just as dominant.
"But these mammals have been here for at least 60 million years so there would have been some diversifying of these creatures."
The mammal discovered at St Bathans did not fall into the three groups of mammals living today: Placentals such as sheep and humans, marsupials such as possums and kangaroos and monotremes such as platypuses.
The bones were a femur and two lower jaws. Each bone was a few millimetres long.
No teeth could be found.
Mr Tennyson said early mammals had evolved from reptiles about 200 million years ago but, by using a scanning electronic microscope, it was quite clear these bones were from a mammal.
He said the sites scattered around St Bathans were first discovered in 1978 by Dunedin geologist Barry Douglas and had been visited annually since 2001 by a team made up of scientists from New Zealand and Australian institutions.
A team of about 20 is set to visit sites next month for about 10 days.
Mr Tennyson said the Australian Government was contributing $500,000 towards the visits.
Up to two tonnes of sediment will be sent back to Australia for analysis but will be returned to New Zealand.
An application by Mr Worthy for $200,000 for four years' research at the sites was turned down last year by the Foundation of Research, Science and Technology.
* Previously, New Zealand had been seen as a land of birds.
* It was thought no ground mammals were present when the country was first formed.
* But the discovery of the mouse-size mammal shows they did exist at least from 82 million years ago when NZ broke away from the Gondwana land mass.
* The fossil find is seen as one of the most important in New Zealand's history.
- OTAGO DAILY TIMES