Moa eggshell scattered across the floor is how the cave got its name, and it turned out to be the least interesting thing in there.<\/p>\n
Moa Eggshell Cave sits near Waitomo on New Zealand\u2019s North Island, roughly 280 metres above the stream that eventually sliced the old cave in two and exposed its buried sediment. Beneath that eggshell, in a layer nobody had reason to sieve until recently, lay a bird community with no modern equivalent anywhere: an early parrot, a giant flightless rail, a pigeon with Australian cousins, and enough absences to suggest the place was emptied and restocked long before people arrived.<\/p>\n
How volcanic ash dated the bones<\/p>\n
A haul of twenty-one usable bone fragments isn\u2019t much to work with. What made them valuable was the packaging.<\/p>\n
Those bones sat between two layers of volcanic ash whose ages were already nailed down. Eroded remnants of the Ngaroma ignimbrite, about 1.55 million years old, still cling to the roof and walls. Above the fossils lies a thick band of ash washed in from the Kidnappers eruption, roughly one million years old. A stalagmite growing on top of the sediment, dated to 535,000 years, closes the timeline from the other end. The full sequence is set out in a paper published in Alcheringa: An Australasian Journal of Palaeontology<\/a> by a team led by Trevor Worthy of Flinders University with Paul Scofield of Canterbury Museum.<\/p>\n Fossil deposits with hard brackets at both ends are rare. The same ash on the walls makes this the oldest cave yet recognised on the North Island.<\/p>\n A parrot with weaker legs<\/p>\n Twelve bird taxa came out of the deposit, two of them new to science. First up is Strigops insulaborealis, an early relative of the k\u0101k\u0101p\u014d, the heavy nocturnal parrot that survives today only on predator-free islands and sanctuaries.<\/p>\n Its foot bones are the giveaway. Modern k\u0101k\u0101p\u014d have powerful legs for climbing and walking. This older bird\u2019s legs were weaker, which hints it spent less time hauling itself up trees and may still have kept some capacity for flight. Worthy\u2019s team is cautious on that point, and rightly so. A handful of bones from one cave can only suggest when the lineage lost flight. Confirming it will take more material.<\/p>\n A rail named after a fence<\/p>\n The second new species, Porphyrio claytongreenei, is a large flightless rail, and its name honours Warren Clayton-Greene, the landowner who fenced the site to keep goats out and helped haul gear up to the dig. It belongs with the living takah\u0113 and the extinct moho, the North Island takah\u0113 known only from bones and a single disputed specimen. The authors float the possibility that it was ancestral to both, with the two lines splitting once Cook Strait separated the islands.<\/p>\n A third bird was a pigeon related to the Australian bronzewings, the first of its kind ever recovered from New Zealand\u2019s fossil record, per coverage of the dig<\/a>.<\/p>\n Frogs that barely changed<\/p>\n Four species of native frog showed up in the same layer, all in the genus Leiopelma, and all recognisable as the frogs still hopping around New Zealand today. Birds churned. Frogs sat tight. Why one group turned over while the other held steady is not resolved in the paper, though small damp animals living in leaf litter plausibly ride out upheaval better than large birds tied to a particular kind of forest.<\/p>\n What reshuffled the forest<\/p>\n \u201cThe shifting forest and shrubland habitats forced a reset of the bird populations,\u201d Scofield said<\/a> when the work was announced in January.<\/p>\n Two forces are in the frame. Glacial and interglacial swings grew sharper through the Early Pleistocene, dragging forest and shrubland back and forth across the landscape. Then there was the volcano. The Kidnappers eruption came from the Mangakino volcanic centre<\/a> and moved something like 1,200 cubic kilometres of magma, laying down what geologists rate as the most widespread ignimbrite sheet on the planet, tens of thousands of square kilometres of the North Island under ash.<\/p>\n Scofield and his colleagues think that upheaval did more than empty out the forest. In comments to Discover<\/a>, he credited it with helping drive the evolutionary diversification of the region\u2019s birds as well.<\/p>\n Between a third and a half of the bird species recovered here appear at no younger fossil site in the country. Worthy\u2019s team consider this an entirely separate community of birds from the one people encountered on arrival roughly a million years later. Those humans landed about 750 years ago, and had nothing to do with any of it.<\/p>\n Where that leaves the k\u0101k\u0101p\u014d<\/p>\n One lineage in the cave made it all the way through: the supereruption, the ice-age reshuffling, whatever happened to the eleven bird species alongside it. It then nearly went extinct anyway, undone across a few generations by cats, stoats and rats, the sort of threat no volcano ever managed.<\/p>\n