Here’s what you’ll learn when you read this story:

• A New Zealand cave has revealed million-year-old fossils, including 12 ancient bird species and four frog species.
• Experts believe the discovery shows how drastically New Zealand’s forest culture has shifted.
• Researchers said up to 50 percent of species on Aotearoa’s North Island went extinct before humans arrived.

A spectacular trove of fossils discovered in a cave on New Zealand’s North Island has given scientists their first glimpse of ancient forest species that lived there more than a million years ago. The fossils represent 12 ancient bird species and four frog species, including several previously unknown bird species. Taken together, the fossils paint a picture of an ancient world that looks drastically different than it does today. The discovery also fills in an important gap in scientific understanding of the patterns of extinction that preceded human arrival in New Zealand 750 years ago.

The team published a study on the find in Alcheringa: An Australasian Journal of Palaeontology in January.

“This is a newly recognized avifauna for New Zealand, one that was replaced by the one humans encountered a million years later,” Trevor Worthy, lead study author and associate professor at Flinders University, said in a statement. “This remarkable find suggests our ancient forests were once home to a diverse group of birds that did not survive the next million years.”

The team located the fossils between two layers of volcanic ash preserved in the cave, each from a different major eruption, the first 1.55 million years ago and the second 1 million years ago. Many of the species represented among the fossils had already gone extinct by the time humans arrived on the island. By extrapolation, the research team estimated that between 33 and 50 percent of all species on the island went extinct during the million years before humans arrived in New Zealand, likely thanks to rapid climate shifts and cataclysmic volcanic eruptions, said Paul Scofield, study co-author and Canterbury Museum senior curator of natural history.

Worthy said that “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.”

Of all the finds, scientists might be the giddiest about discovering a new species of parrot, Strigops insulaborealis, an ancient relative of the iconic Kākāpō, a large flightless parrot known for its heft. The team believes this ancestor may have possessed the ability to fly. By analyzing the fossil discovery, the team noticed the ancient bird had weaker legs than the modern relative, implying the ancestor wasn’t quite the skilled climber as the modern-day Kākāpō. Still, the team said more research is needed to confirm that this ancient bird could fly.

The researchers also uncovered an ancestor of the modern Takahe, which opens further research into that bird. Fossils of an extinct species of pigeon closely related to the Australian bronzewing pigeons also excited experts.

“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.”

Scofield said that previous excavations showed life in New Zealand between 20 and 16 million years ago and that by contrast, the new discoveries offer the first evidence of life from 15 million years ago to one million years ago. “This wasn’t a missing chapter in New Zealand’s ancient history,” Scofield said, “it was a missing volume.”