“Have kiwi been in New Zealand since our continent (Zealandia) broke away from Gondwana, or did they arrive here more recently?”
– Brian I.
For the answer to this one we turned to historical biogeographer, and author of Ghosts of Gondwana, Dr George Gibbs:
I am not at all surprised that you are unclear! So is everyone. The speculation about kiwi ‘arrival on Zealandia’ is fuelled by molecular biologists and the variable results that have been published to date. What does seem clear is that kiwi biogeography is quite independent from moa. They represent two separate lineages that each have independent histories in this part of the world. The open questions are when they first colonised Zealandia and did they have to walk?
There is no fossil evidence to assist this speculation. Molecular biology affirms that kiwi diverged from the emu/cassowary lineage in Australia, but gives variable estimates for the timing of this separation (from 68-60 million years ago). The early (e.g. Alan Cooper ca 1990) estimates were back far enough for it to have walked into Zealandia as the land separated from the rest of Gondwana. But more recent estimates with revised methodologies suggest that the timing of kiwi divergence was could have been after Zealandia separated (i.e. less than 60 million years ago). This date, plus a revised phylogenetic tree which shows that flight could have been lost during kiwi evolution, can be interpreted as ‘evidence’ that kiwi might have flown to New Zealand across the ocean.
So that is where we stand at present. There are no fossils to provide empirical scientific evidence. And we have a range of hypotheses giving ‘just-so’ stories of origins. I think the Aussie origin from emu stock will stick, but I personally still have doubts about the wing story. My own feeling is that kiwi was probably separated from its ancestors before the last tenuous land links between Zealandia and Australia finally broke. The kinds of terrestrial life that survived on Zealandia prior to the uplift that raised the Southern Alps can only be guessed at. There are no shoreline maps and we have yet to discover where former land existed and how much persisted through the so-called ‘drowning’ era that has been such a topic of discussion recently. What we do know is that some land has always been present. Thus there is no need to postulate that kiwis had to fly to reach New Zealand!