A newly discovered extinct duck may be key to dating other ancient finds in St Bathans.

Researchers working together - from Canterbury Museum and three Australian universities - were excited at the impact of the discovery on understanding the region's natural history.

An artist's impression of a Manuherikia duck. Photo: Canterbury Museum / Tom Simpson

The small diving duck has been given the name Manuherikia primadividua, and appears to have lived between 16 and 19 million years ago.

It was found in an ancient lakebed in St Bathans, Central Otago.

St Bathans holds the most known fossils of land-based animals in Aotearoa, which are rarely discovered in this country.

Flinders University of Adelaide researcher Trevor Worthy said the crux of this discovery is the positioning of the duck in fossil layers.

"We haven't found these two ducks in the same fossil layer, and we think that's because they lived at different times, with Manuherikia primadividua outcompeting and eventually replacing its older cousin."

The switch in species provides key information about climate and environmental changes at the time.

The find will also allow researchers to order pre-discovered animals chronologically for the first time, with the two ducks in different fossil layers indicating a similar story for other species.

Canterbury Museum senior curator Paul Scofield said the discovery emphasised the importance of understanding which layer a fossil was positioned in.

"You might think, 'Oh, it's just another dead duck', but it's an important step in building up a picture of how the animals and plants living on this ancient lake changed over time."

Excavations at the St Bathans lakebed have taken place since 2001, where scientists have found over 40 ancient bird species.

Fossils of bats, turtles and a crocodile have also been discovered, upending assumptions about the evolution of natural fauna in Aotearoa.