A cave on New Zealand’s North Island has revealed a fossil assemblage dating back more than one million years, exposing the remains of an ancient forest ecosystem. The discovery includes birds and frogs that no longer exist in the region, along with several species previously unknown to science.
The fossils were uncovered in sediments inside a cave system that acted as a natural archive over vast stretches of time. What makes the site unusual is the precision of its geological framing, with volcanic ash layers sealing biological material in place. This allowed scientists to reconstruct fragments of ecosystems that once occupied the North Island but have since disappeared entirely.
For decades, the pre-human ecological history of New Zealand was understood only in fragments, with large gaps between older fossil records and more recent biological evidence. The study published in Alcheringa: An Australasian Journal of Palaeontologyhelps bridge part of that gap, extending knowledge of local biodiversity into a period that was previously poorly documented.
Fossils Locked Between Volcanic Eruptions
The remains were found between two distinct volcanic ash layers, one dated to about 1.55 million years ago and the other to roughly 1 million years ago. These deposits created a natural time capsule that preserved bones from birds and frogs that once lived in forest and shrubland environments.
The research team identified12 bird species and four frog species in the cave sediments, including several bird species not previously recorded. The diversity points to a complex ecosystem that existed during a period of environmental instability on the island. Lead author Trevor Worthy, associate professor at Flinders University, said in a statement that:
“This is a newly recognized avifauna for New Zealand, one that was replaced by the one humans encountered a million years later.”
He also stated that the fossil evidence points to ancient forests that supported a wide range of birds that later disappeared without leaving modern descendants in many cases.
Extinction Before Human Arrival
The study suggests that a large proportion of New Zealand’s species loss occurred well before human settlement, which began about 750 years ago. Researchers estimate that between 33 and 50 percent of species on the island went extinct during the million years preceding human arrival.
“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,” co-author Paul Scofield of Canterbury Museum explained.
This interpretation changes how extinction on the island is understood, showing it as a long-term process rather than something driven only by human arrival. The fossil record points to repeated breaks in ecological continuity, with species groups shifting significantly over time.
The findings also help show how New Zealand’sunique wildlife developed in isolation, shaped by repeated environmental changes instead of a steady, long-term evolution.
Birds That Changed Evolution
Among the most notable discoveries is a newly identified ancient parrot, Strigops insulaborealis, considered an early relative of the modern kākāpō. The fossil suggests differences in limb structure, with weaker legs than the modern species, raising the possibility that it may have been capable of flight, though this remains under investigation.
The site also yielded fossils of an ancestor of the modern takahē, adding new information about the evolutionary history of this large flightless bird. In addition, researchers identified an extinct pigeon species closely related to Australian bronzewing pigeons, expanding the known distribution of these lineages in the distant past.
Trevor Worthy noted that the assemblage shows New Zealand’s ancient forests hosted a far more varied bird community than previously understood. Scofield added that:
“This wasn’t a missing chapter in New Zealand’s ancient history,” he said, “it was a missing volume.”
