Dating fossil duck species helping with other finds

The fossilised remains of a duck found in an ancient lake bed near St Bathans is not only a newly discovered species, but could be key to dating other finds discovered nearby.

The new species, a small diving duck researchers have named Manuherikia primadividua, lived between 16million and 19million years ago on a huge palaeolake, Lake Manuherikia.

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M. primadividua was the first fossil found at St Bathans that could help researchers narrow down dates for other finds.

Flinders University, Adelaide, Associate Prof Trevor Worthy is the lead author of a paper recently published in the peer-reviewed journal Geobios describing the bird.

The duck appeared to have replaced another, related duck species, Manuherikia lacustrina, at some point in the three-million-year period preserved in the fossil record at St Bathans.

"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 duck species may well occur at the same time as a change in the vegetation in the region, revealed by pollen studies years ago by Mike Pole and Barry Douglas. If so, this may be evidence of climate change affecting the St Bathans fauna."

Canterbury Museum natural history senior curator Dr Paul Scofield, one of the paper’s co-authors, said the two ducks would allow many of the other finds from St Bathans to be dated.

"If we find a new species alongside M. lacustrina fossils, we know it lived in this earlier period, whereas if it’s alongside the new species it lived a bit later," Dr Scofield said.

"You might think, ‘Oh, its 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," Dr Scofield said.

Fossils of animals that lived in the sea are relatively common in New Zealand, but the remains of ancient land-based animals are extremely rare.

The ancient lake bed at the site is the most significant known deposit of land-based animal fossils in the country.

Excavations at St Bathans that started in 2001 had unearthed more than 40 ancient bird species, including the giant, possibly carnivorous parrot Heracles inexpectatus.

Scientists also found bats, turtles and a crocodile - discoveries which upended what they thought they knew about the evolution of New Zealand’s fauna.

Manuherikia primadividua is one of four ducks in the genus Manuherikia that palaeontologists have found at St Bathans, and one of nine waterfowl species.

The species name, primadividua, was given by the palaeontologists to acknowledge that the duck provides the first evidence of a chronological division in the St Bathans fauna.

The Manuherikia primadividua fossils are held by Canterbury Museum and the Museum of New Zealand Te Papa Tongarewa.