Associate Professor Nic Rawlence, Director of the Otago Palaeogenetics Laboratory, is a co author of the new study, which investigates the fossil and its evolutionary relationships.

The research, published in Historical Biology, was carried out by an international team from the University of Otago, the Museum of New Zealand Te Papa Tongarewa, and the University of Cambridge (UK). The scientists examined fossil material recovered from the well known St Bathans fossil deposits.

A New Species Hidden Among Fossils

Rawlence explained that although waterfowl fossils are abundant at St Bathans, goose remains are much less common.

To investigate further, the team re examined every fossil bone previously identified as belonging to geese. They compared those remains with other fossil waterfowl from the site as well as an extensive collection of modern and extinct bird skeletons.

"We determined that the bones included an undescribed species, the size of a small goose," he says.

The newly identified bird has been named Meterchen luti. Its name is inspired by the nursery rhyme Old Mother Goose, reflecting the idea of an ancient goose emerging from the mud of a fossil deposit. Meterchen means "mother goose" in ancient Greek, while luti is Latin for "of the mud."

Rawlence noted that "The St Bathans goose is not closely related to the recently-extinct giant flightless New Zealand geese (Cnemiornis species) or their Australian cousin, the Cape Barren goose."

Rethinking New Zealand Bird Evolution

Combined with recent genetic evidence, the discovery suggests New Zealand's bird history is much more complex than scientists once assumed.

Lead author Alan Tennyson of Te Papa said many bird species have reached New Zealand over millions of years, but the ancestors of some of the country's best known large birds arrived surprisingly recently. Those more recent arrivals, dating back only four to five million years, include takahē, Forbes' harrier, and the giant Haast's eagle.

"An earlier theory argued that the St Bathans goose represented the direct ancestors of giant flightless Cnemiornis geese, implying this lineage had a very long history (of at least 14 million years) in Zealandia," he says.

"However, this conflicts with genetic evidence suggesting the ancestors of Cnemiornis arrived from Australia only about seven million years ago, which proponents of the earlier theory discarded.

"Our rigorous reassessment supports the later arrival theory."

DNA and Fossils Reveal a More Dynamic Past

According to Rawlence, the ancestors of the St Bathans goose reached Zealandia more than 14 million years ago, but their lineage eventually disappeared without leaving surviving descendants.

"Using all the tools in the toolbox, including DNA and fossils, we can reconstruct how the dynamic geological, climatic and human history of Zealandia has shaped the evolution of Aotearoa fauna in ever more detail," he says.

He added that the giant flightless Cnemiornis geese provide another remarkable example of how quickly island species can change.

"The relatively recent evolution of the giant flightless Cnemiornis geese offers another striking example of rapid morphological change that can occur within a short timeframe on islands. At one metre tall and weighing up to 18kg, these were the largest geese in the world."