Australian and New Zealand researchers will return to a "treasure trove" of fossils in Central Otago in early January in the hope of casting further light on the "ghost lineages" of ancient mammals.
The Manuherikia lakebed - now sandstone - on a privately owned farm near St Bathanshas already produced tiny bones of a mouse-like creature identified this week as the world's most primitive type of land mammal.
The mammal discovery was reported this week by former Masterton palaeontologist, Trevor Worthy - now at Adelaide University - and Alan Tennyson, a palaeontologist from the Museum of New Zealand in Wellington, in America's Proceedings of the National Academy of Sciences.
New Zealand separated from the ancient continent Gondwana some 82 million years ago, and until now land mammals were thought to have arrived only after humans.
The mouse-size creature, which is 16-19 million years old, is evidence that mammals did exist here at one time.
So far, the fossil-hunters have examined only a fraction of the ancient lakebed and next month's "dig" would be able to make only a small dent in the area remaining to be investigated. The lake was originally about nine times the size of Lake Taupo.
The rocks have already yielded fossil records of cockabullies, whitebait and freshwater mussels as well as bones of tuatara, skinks, geckos and bats. The lakebed has also surrendered the remnants of 22 previously unknown extinct bird species.
"We await with bated breath what we find next," said Mr Tennyson. "Hopefully in January we will get a whole lot more."
