A cave near Waitomo has opened a new window into Aotearoa New Zealand’s deep past, with scientists finding animal remains about 1 million years old, including a previously unknown ancestor of the kākāpō.

The fossils come from a large collection inside the North Island cave and include remains from 12 species of birds and four species of frogs. Researchers say the site offers a rare look at what New Zealand’s ecosystems looked like at that time.

The work, published in Alcheringa: An Australasian Journal of Palaeontology, says dramatic climate shifts and major volcanic eruptions shaped the country’s wildlife long before humans arrived. The research says those natural events led to repeated extinctions and the rise of new species.

Lead author Trevor Worthy, a Flinders University associate professor from the College of Science and Engineering, said the fossils reveal a part of New Zealand’s biodiversity that had not been recognised before.

“This is a newly recognized avifauna for New Zealand, one that was replaced by the one humans encountered a million years later,” Associate Professor Worthy said.

“This remarkable find suggests our ancient forests were once home to a diverse group of birds that did not survive the next million years.”

Paleontologists from Flinders University and Canterbury Museum examined the fossils with volcanologists Joel Baker from the University of Auckland and Simon Barker of Victoria University of Wellington.

The team estimates that about 33 to 50 percent of species disappeared in the million years before humans arrived in Aotearoa New Zealand.

Canterbury Museum senior curator of natural history, Paul Scofield, said fast environmental change played a major role.

“These extinctions were driven by relatively rapid climate shifts and cataclysmic volcanic eruptions,” Scofield said.

“From our excavations at St Bathans in Central Otago over many years, we have a snapshot of life in Aotearoa between 20 and 16 million years ago. These new findings cast light on the 15 million-year period from then to 1 million years ago, which is largely absent from New Zealand’s fossil record,” Scofield said.

“This wasn’t a missing chapter in New Zealand’s ancient history, it was a missing volume.”

Among the most notable finds is a newly identified parrot species, Strigops insulaborealis, described as an ancient relative of the modern kākāpō. Researchers say that, unlike today’s heavy, flightless kākāpō, this earlier species may have been able to fly.

Fossil analysis suggests it had weaker legs than the modern bird, which indicates it was likely less suited for climbing. The researchers say more study is needed to confirm if it could truly fly.

The cave also held fossils of an extinct ancestor of the takahē, which the researchers say helps explain the evolution of that bird. The team also found an extinct pigeon species closely related to Australian bronzewing pigeons.

Scofield said changing habitats reshaped bird life in the North Island.

“The shifting forest and shrubland habitats forced a reset of the bird populations,” Scofield said.

“We believe this was a major driver for the evolutionary diversification of birds and other fauna in the North Island.”

Scientists dated the fossils because they were preserved between two separate layers of volcanic ash inside the cave. One layer is linked to an eruption about 1.55 million years ago, and the other to a massive eruption around 1 million years ago.

The later eruption likely spread metres of ash across much of the North Island, according to the research. While much of that ash was later washed away, some stayed protected inside caves.

The older ash layer also shows that the site is the oldest known cave in the North Island.

Associate Professor Worthy said the fossils fill a major gap in the record of the country’s past. He said the remains “provide a critical, missing baseline for New Zealand’s natural history.”

“For decades, the extinction of New Zealand’s birds was viewed primarily through the lens of human arrival 750 years ago. This study proves that natural forces like super-volcanoes and dramatic climate shifts were already sculpting the unique identity of our wildlife over a million years ago.”