Fifteen years ago a research group started digging fossils from a St Bathans archaeological site. Central Otago reporter Jono Edwards talks to the excavators about how a patch of Central Otago farmland is being used to piece together the country's past.
When researchers began digging in a patch of ordinary Maniototo farmland, they did not realise the extent to which New Zealand's prehistoric mysteries could be solved by what lay encased in the ground.
Every summer for 15 years, an archeological site at St Bathans, on private land near the Manuherikia River, has been visited by a team led by Te Papa vertebrate curator Alan Tennyson, Canterbury Museum natural history senior curator Paul Scofield and New Zealand vertebrate palaeontologist Trevor Worthy, who is based at Flinders University Adelaide.
They most recently visited for about two weeks last month, with about three or four people on site at one time.
There is a large gap in our knowledge of extinct New Zealand animals from the time of dinosaurs, 65 million years ago, until about a million years ago.
This research team has been filling some of that gap, specifically the Miocene period about 16 million to 19 million years ago.
In their excavations they have identified more than 70 new species, including birds, bats, fish, lizards, molluscs and a turtle.
Dr Tennyson says over the years the team has cracked through layers of rock with simple tools, bringing in a digger for the heavy-duty work.
Most of their work these days, however, is done on a soft clay bank, where they will take sediment and sift it in the nearby river.
An exciting curve-ball came 10 years ago with the discovery of a femur and jaw bones belonging to a creature dubbed the "waddling mouse''.
The existence of the rodent-like animal was counter to the common theory that New Zealand had no land mammals after its split from Gondwana, until the first Polynesian settlers arrived bearing rats about 800 years ago.
But Dr Scofield says they are in two minds over whether the creature is a mouse or a bat.
"If it was a bat it probably acted a lot like a rat or mouse and was maybe incapable of flight.''
Dr Tennyson says on every excavation since they have hoped to find more pieces to complete the puzzle.
"Since then we've found a better femur and some tantalising teeth, which could well be related.''
Another key quest is to find a crucial piece of crocodilian skull.
The digs are funded by Te Papa and the Canterbury Museum, although the Australian Research Council has also contributed in the past.
Dr Scofield says on the first visit in 2001, they hoped to find at least one identifiable bird bone.
"But in half an hour we'd already found four or five.''
Euan Johnstone, whose 2000ha Home Hills Station hosts one of the main dig sites, says it was "quite a surprise'' to him and his wife Ann when the team first asked to dig on their land.
"It is exciting, but it doesn't mean much to me because I'm not a scientist.
"We have a good relationship. I keep an eye on what they're doing and they keep us updated.''
He gives all the help he can, he says.
"We want to help them to find what they're looking for.''
Mr Johnstone even helped the team dig on occasion but "didn't really know what to look for''.
One of the early discoveries was named the Johnstones' duck after the couple.
And it is the ducks, as well as geese, which Dr Tennyson says are findings of global importance.
"This collection of water fowls I believe is the richest in the world from that era.''
The bones are tiny, at a few centimetres, and they will never get a fully formed skeleton, but one bone is "very diagnostic'' as to what form the rest of the body will take, he says.
Sometimes, the piece does not predict the puzzle.
"In the early days a tooth was found by another team. It was identified by Aussie experts as a snake tooth. But eventually we found more hook teeth like it and found it was a from a fish.''
Dr Scofield says they usually leave with about two tonnes of sediment which they have to dig through grain by grain.
Fossils are then analysed by Flinders University, and more recently at Canterbury Museum.
Dr Scofield says the lake which once covered the site was probably young when these species existed, as the acidity of older lakes destroys remains and can turn plants into coal.
"Although there is coal in the area. I think the chronology goes that it was while coal mining company Coal Corp was there in the '70s that the first bird bones were found.''
Numerous discoveries later, and with half of the fossils found unidentified, Dr Tennyson says the excavations will go well into the future.
"We're not planning on stopping. There is nothing else like it in New Zealand.''
