Chuck Landis at his home in Otago, New Zealand. He believes New Zealand sank beneath the waves before being re-colonised by drifting species.
Credit: Bill Morris
Chuck Landis lays a map down on his kitchen table, the cold ocean murmuring just beyond the lawnmower shed. "I just can't believe it hasn't been more questioned," he says. "It's not sound science."
The map on Chuck's table shows what New Zealand might have looked like 30 million years ago, during the Oligocene period. It was lower, with only a few small islands visible.
Long before the mountains were forced up, New Zealand was the dry scalp of a drowned continent. When sea levels rose during the warm Oligocene, most of it was submerged.
The textbook says animals and plants had ridden the land-mass since it broke away from an ancient super continent called Gondwana. The beasts and botany clustered together on the small remaining islands until the sea level fell again. More than just a scientific theory, this idea is woven into New Zealand's national identity: a fragment of an ancient land, a time capsule in the South Pacific - that's the Kiwis.
But Chuck is a scientist - a geologist with a critical eye for such enshrined truths. There is no evidence, he argues, any land at all remained above water during the Oligocene flood. The patches outlined on the map were demarcated because they contain no marine sediments for that period, but there is no conclusive evidence for land-based life either. No fossils, no coal deposits, nothing but hard schist.
The existence of these islands is argued for on the basis of plants and animals - those iconic creatures that adorned New Zealand's classrooms. The moa, flightless for so long evolution stripped it of even a trace of a wing-bone. The lizard-like tuatara, a creature so ancient it pre-dated the dinosaurs. How else could they be here, were it not for the continuous existence of dry-land since the break-up of Gondwana?
"I don't get steamed up about the animals," says Chuck. "And I know it bothers people, but I don't!" He does, however, admit the presence of the large, flightless moa poses a "big problem".
While more than one scientist has suggested the moa's ancestors might have flown to New Zealand and subsequently lost the power of flight, the total absence of a wing-bone in moa skeletons remains a sticking point. However, many now believe the movement of species between land-masses may be far more fluid than we ever imagined.
Chuck is studying the Chatham Islands, a remote collection of rocks 800 km off the East Coast of New Zealand. These islands were totally submerged in the Oligocene, yet support a diverse flora and fauna, most of which is closely related to that of mainland New Zealand. According to Chuck, all of these species arrived by dispersal - riding the waves or prevailing westerlies.
One day, while walking a windswept Chatham Islands coast, Chuck found a willow tree thrashing about in the surf. There are no willows on the Chathams - it had to have floated from the mainland. There is no reason, he argues, a beech tree couldn't have made the same journey; no reason insects, birds, plants and animals couldn't have gone along for the ride.
It only takes one breeding pair, one pregnant female, or one batch of seeds, to start a population. Improbable? Yes, but just because something is unlikely to occur in our lifetime, doesn't make it so in the vast reach of geological time. A lot of 'improbable events' can happen in 30 million years.
The idea of dispersal is not new. In Darwin's day, it was the only way to explain how similar species came to exist on chunks of land divided by wide oceans. Then in the 1960s the world came to accept plate tectonics. Continents breaking apart was an obvious way for plants and animals to become separated, and dispersal was sidelined as an inconvenience, a bit of static against the real science of vicarious distribution. The problem is, it's very difficult to prove dispersal events. While fossil records can give a clear picture of shifting continents and the species that lived on them, plants and animals that simply washed up are much harder to pin down.
However, improvements in DNA sequencing and molecular analysis have allowed scientists to determine more accurately how long divergent species have been separated. This has overthrown many of the old assumptions about species being torn apart by continental drift and evolving on their own. It turns out many forms of life, isolated by oceans, have diverged too recently to have simply ridden the break-up of land-masses.
Matt McGlone, a palaeoecologist with Landcare Research, a government owned institute, has written a paper entitled "Goodbye Gondwana," in which he roundly criticises those who claim New Zealand's evolutionary heritage is uniquely Gondwanan.
"Let's think about it," he says. "The transformations New Zealand's gone through. We started almost in the polar circle, albeit with a mild climate. Then we floated north, and there were coconut trees and corals here. Later we developed into a cool-temperate oceanic land-mass. "What are the chances a species could survive all that?"
Eleven years ago, Kiwi botanist Mike Pole, now at the University of Queensland, presented a paper in which he argued it was entirely plausible New Zealand's entire flora and fauna arrived via dispersal. He pointed out that DNA analysis of the now-flightless kiwi suggests it diverged from its closest relatives, the Australian emus and cassowaries, less than 45 million years ago, long after the continents split. This would suggest its ancestors must have flown, floated, or at least 'island-hopped' to New Zealand.
Nothofagus, the beech tree that clothes New Zealand's southern mountains, is often termed 'Gondwanan', as its relatives are found in Tasmania and Chile. Yet one species of Nothofagus pollen turns up in Australia's geological record after the two separated, indicating the tree reseeded itself in the Australia despite the widening ocean barrier. Indeed, according to Mike Pole, the fossil records of Australia and New Zealand point to a continuous flow of plant species from west to east across the Tasman Sea.
"30 or 40 million years ago, Australia was completely covered in rainforest," he says. "And there were huge rivers, huge piles of vegetation flooding out there, and it just floated across to New Zealand."
Punctuating the Pacific, volcanic islands have never been connected to continental landmasses. The fauna of Lord Howe Island, in the Tasman Sea, includes such landlubbers as tortoises (now extinct) and snails. This place was sizzling lava emerging from the brine just three million years ago, yet its sides are now dense with trees and plants. Of similar age, nearby Norfolk Island inherited its eponymous pine from across the waves, which means the seeds had to travel at least 470 kilometres to get there. How these things arrived is a mystery, but if islands like Lord Howe, Norfolk and the Fiji group can be readily colonised, why not New Zealand?
And then there's Hawaii, alone in the Pacific, 4000 kilometres from any large land-mass. When the intrepid Captain got there, native Hawaiians built houses and tools from 'Ohi'a lehua, the most plentiful tree on the islands. The scarlet blooms must have looked familiar to Cook - the seeds of its ancestors came from New Zealand, probably utilising the unusually strong wind patterns of the ice age to traverse the massive ocean and populate the volcanic domes of Hawaii thousands of years earlier.
Proponents of the vicarious dispersal theory of continents drifting apart are now being criticised for underestimating the importance of wind and water-borne dispersal. A kind of counter-revolution in biogeography is at hand. Chuck Landis and others are taking an axe to the pillar of knowledge that has explained New Zealand's evolutionary heritage since the advent of plate tectonics theory. In arguing New Zealand could well have been colonised by species that drifted or blew in from elsewhere, they're fighting an easy assumption of biogeography that has prevailed for over forty years.
Inland from Chuck's house on the Otago coast of New Zealand's South Island, a wide river valley hangs between broad, flat-topped hills. These hills, says the textbook, are remnants of the Otago peneplain - a flat surface left behind after New Zealand was ground down by millions of years of erosion. Chuck has never believed it. He suspects the 'peneplain' is a wave-cut platform, shaped by the sea as it marched steadily inland, on its way to an overwhelming extinction.
Chuck Landis doesn't really expect to prove New Zealand went under the waves 30 million years ago. He does, however, want to challenge the idea that New Zealand's ecological inheritance is uniquely 'Gondwanan'. He's got a big job ahead.
As Matt McGlone wryly observes, abandoning 'Time Capsule of the South Seas' for 'Fly-paper of the Pacific' could well be a wrench.
Bill Morris wrote this while studying at the Centre for Science Communication, University of Otago, New Zealand
