Remarkable fossils discovered in a cave near Waitomo on New Zealand’s North Island are giving scientists an unprecedented look into a long-vanished ecosystem. Researchers in Australia and New Zealand have discovered fossilized remains of ancient birds and frogs that lived about a million years ago, including a previously unknown relative of the iconic kakapo.
The discovery marks the first time scientists have recovered a large collection of terrestrial vertebrate fossils from this period in New Zealand’s history. The cave contains fossils of 12 bird species and four frog species, providing a rare snapshot of the world as it existed hundreds of thousands of years before humans arrived on the island.
This research Alkeringa: Australian Journal of Paleontologysuggests that New Zealand’s wildlife was already undergoing dramatic changes long before humans settled. Powerful volcanic eruptions and rapid climate change are causing repeated habitat restructuring, promoting extinctions and opening opportunities for new species to evolve.
Ancient birds forgotten by time
Lead author Associate Professor Trevor Worthy from Flinders University said the fossils revealed a different bird community to that seen in New Zealand today.
“This is a newly recognized bird species in New Zealand, replacing a bird species encountered by humans a million years later,” says Associate Professor Worthy, from Flinders University’s School of Science and Engineering.
“This surprising discovery suggests that our ancient forests were once home to a wide variety of bird species, but they were unable to survive for millions of years.”
In biology, the term “avifauna” refers to the collection of birds that live in a particular place and time. These fossils show that the birds that lived in New Zealand a million years ago were very different from those that existed around the time humans finally arrived.
The study involved paleontologists from Flinders University and Canterbury Museum, as well as volcanologists Joel Baker from the University of Auckland and Simon Barker from Victoria University of Wellington.
Around 33 to 50 per cent of species disappeared in the one million years before humans arrived in Aotearoa New Zealand, researchers say.
Ecosystems reshaped by volcanoes and climate change
Scientists believe that these losses were primarily caused by cataclysmic changes in the natural environment.
“These extinctions were caused by relatively rapid climate change and catastrophic volcanic eruptions,” says co-author Dr Paul Schofield, Curator of Natural History at Canterbury Museum.
This discovery helps fill in one of the biggest gaps in New Zealand’s fossil record.
“Years of excavation at St Bathans in Central Otago has provided a snapshot of life in Aotearoa between 20 million and 16 million years ago. These new discoveries shed light on a period of 15 million years between then and 1 million years ago that is largely missing from New Zealand’s fossil record,” Dr Schofield said.
“This wasn’t a missing chapter in New Zealand’s ancient history; it was a missing volume.”
Fossils are often compared to the pages of Earth’s history book. In this case, researchers say they have uncovered a whole part of the story that was previously unknown.
Possible flying ancestor of the kakapo
One of the most exciting discoveries is a newly identified parrot species. Strigops insulaborealis. It is an ancient relative of the kakapo, one of New Zealand’s most famous birds.
Currently, the kakapo is the only flightless parrot in the world. It is also one of the heaviest parrots and is known for its unusual nocturnal lifestyle. But the newly discovered ancestor may have been very different.
Analysis of fossilized bones suggests that its legs were weaker than those of modern kakapo. Because modern birds rely heavily on their strong legs and ability to climb, researchers believe that ancient species may have spent less time climbing and retained the ability to fly.
Additional research will be needed to determine whether it can actually fly.
The cave also contained fossils of an extinct ancestor of the takahe, another New Zealand endemic bird. Researchers also identified an extinct pigeon species closely related to the Australian green pigeon.
“Changes in forest and shrub habitat have caused bird populations to reset,” Dr Schofield added.
“We believe this was a major driver of the evolutionary diversification of North Island birds and other fauna.”
Volcanic ash helps date fossils
One reason this discovery is so important is that it allows scientists to determine its age with unusual precision.
The fossils were trapped between two layers of volcanic ash that were preserved inside the cave. One layer of volcanic ash was created by an eruption about 1.55 million years ago. The second one was caused by a major eruption about a million years ago.
This natural geological sandwich clearly indicates age limits for fossils.
Researchers say this young eruption likely covered much of the North Island with several meters of volcanic ash. Rain and erosion eventually removed much of the material, but some remained protected within the cave.
The layer of old ash reveals something even more remarkable. It indicates that this fossil site is the oldest known cave on New Zealand’s North Island.
Rewriting New Zealand’s natural history
Associate Professor Worthy said the fossil was an important reference point for understanding how New Zealand’s wildlife evolved.
The fossil “provides an important reference point that is missing in New Zealand’s natural history”.
For years, scientists have largely focused on the ecological changes that occurred after humans arrived in New Zealand about 750 years ago. New evidence shows that powerful natural forces have already been transforming the island’s wildlife for hundreds of thousands of years.
“For decades, the extinction of New Zealand’s birds has been viewed primarily through the lens of the arrival of humans 750 years ago. This study proves that natural forces such as giant volcanoes and dramatic climate change were already shaping the unique identity of our wildlife more than a million years ago.”
