A cave near Waitomo has opened a window onto a New Zealand that vanished about 1 million years ago.
Researchers from Australia and New Zealand say fossils from the North Island cave include the remains of 12 bird species and four frog species, including a previously unknown relative of the kākāpō. They say it is the first large collection of terrestrial vertebrate fossils from this period found in New Zealand.
The research was published in Alcheringa: An Australasian Journal of Palaeontology.
Lead author Associate Professor Trevor Worthy of Flinders University said the fossils point to a bird community very different from the one later encountered by humans.
“This is a newly recognized avifauna for New Zealand, one that was replaced by the one humans encountered a million years later,” says Associate Professor Worthy, from the College of Science and Engineering at Flinders University.
“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 researchers said about 33 to 50 percent of species disappeared during the million years before humans reached Aotearoa New Zealand.
Co-author Dr Paul Scofield, senior curator of natural history at Canterbury Museum, said natural upheaval drove those losses.
“These extinctions were driven by relatively rapid climate shifts and cataclysmic volcanic eruptions,” says Dr. Paul Scofield, Senior Curator of Natural History at Canterbury Museum.
The team included paleontologists from Flinders University and Canterbury Museum, along with volcanologists Joel Baker of the University of Auckland and Simon Barker of Victoria University of Wellington.
Dr Scofield said the discovery fills a major gap in the fossil record.
“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,” says Dr. Scofield.
“This wasn’t a missing chapter in New Zealand’s ancient history, it was a missing volume.”
Among the fossils was a newly identified parrot species, Strigops insulaborealis, described as an ancient relative of the kākāpō.
Researchers said analysis of the fossil bones suggests it had weaker legs than the modern kākāpō. Because living kākāpō rely heavily on strong legs and climbing ability, the team thinks the ancient species may have spent less time climbing and may have retained the ability to fly. They said more research is needed to confirm that.
The cave also held fossils from an extinct ancestor of the takahē and an extinct pigeon species closely related to Australia’s bronzewing pigeons.
“The shifting forest and shrubland habitats forced a reset of the bird populations,” adds Dr. Scofield. “We believe this was a major driver for the evolutionary diversification of birds and other fauna in the North Island.”
The fossils were found between two layers of volcanic ash inside the cave, which helped date them. One ash layer came from an eruption about 1.55 million years ago, and the other from a massive eruption about 1 million years ago.
Researchers said the younger eruption likely covered much of the North Island in metres of ash, and that some of it remained protected inside caves. They also said the older ash layer shows the site is the oldest known cave on New Zealand’s North Island.
Associate Professor Worthy said the fossils “provide a critical, missing baseline for New Zealand’s natural history.”
He said: “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.”
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