Davidson, Steve, Ecos
New Zealanders are fond of the notion that their biota is a fragment of ancient Gondwana. So botanist Dr Mike Pole risks being branded unpatriotic for his argument, first published in 1994, that New Zealand's vegetation arrived by long distance dispersal.
`By this, I meant that the ancestors of present plants reached New Zealand after maximum development of the Tasman and Southern Oceans,' says Pole, now at the University of Queensland.
`Anything that was a direct import from Gondwana had probably died out along the way as the land rafted north. In other words, I suggested that there has been a complete biotic turnover at the lineage level.'
This view is provocative, but not so far fetched.
Take a look at the rich vegetation of Norfolk and Lord Howe Islands, all of which must have arrived by sea, because both these oceanic islands are `volcanic piles' of quite recent origin (two and 10 million years ago, respectively) and they have never been attached to other land.
Pole is now revisiting the question of origins, asking how the fossil record helps or hinders his view. For example, the beech genus, Nothofagus, is widely regarded as a `classic' Gondwana group, its global distribution reflecting ancient land connections.
It has a good and superabundant pollen record in New Zealand, but is strangely absent from virtually all fossil pollen samples of the Early Eocene, an 8-million-year gap. One of two things could have happened: either Nothofagus was very rare during this time (an unseen `ghost' group), or it became extinct.
`If it was extinct,' says Pole, `it might be expected that the recolonisation of New Zealand was from nearby Australia, and to some extent this is what we find. Three of the four beech species that appear after the `gap' also occur in Australia'. …