Natural History of New Zealand - Evolution

Evolution

The break-up of the supercontinent of Gondwana left the resulting continents and microcontinents with shared biological affinities. Zealandia (the continental crust from which New Zealand and New Caledonia later developed) began to move away from Antarctic Gondwana 85 Ma ago, the break being complete by 65 Ma ago. It has been moving northwards since then, changing both in relief and climate. About 23 million years ago New Zealand was mostly underwater. One estimate suggests just 18% of the present surface area remained above the water. However geological evidence does not rule out the possibility that it was entirely submerged, or at least restricted to small islands. Today about 93% of the Zealandian continent remains below the sea. Several elements of Gondwana biota are present in New Zealand today: predominantly plants, such as the podocarps and the southern beeches, but also a distinctive insect fauna, New Zealand's unusual frogs and the tuatara, as well as some of New Zealand's birds. It seems likely that some primitive mammals also were part of the original cargo. Whether or not any of these taxa are descendents of survivors of that ancient cargo remains unproven. Recent molecular evidence has shown that even the iconic Gondwanan plants the southern beeches (Nothofagus) arrived in New Zealand after separation of Zealandia from Gondwana. There is a high rate of interspecific and intraspecific hybridisation in New Zealand plants and animals.

The two sources of New Zealand's biodiversity following separation from Gondwana have been speciation and air- or sea-borne immigration. Most of these immigrants have arrived from Australia, and have provided the majority of New Zealand's birds and bats as well as some plant species (carried on the wind or inside the guts of birds). Some of these immigrants arrived long enough ago that their affinities to their Australian ancestors are uncertain; for example, the affinities of the unusual short-tailed bats (Mystacinidae) were unknown until fossils from the Miocene were found in Australia. Cyanoramphus parakeets are thought to have originated in New Caledonia and have been successful at reaching many islands in the region. The link between the two island groups also includes affinities between skink and gecko families.