Until the Early Cretaceous, when the first phases of rifting that preceded the eventual breakup of the Australasian sector of Gondwana occurred, New Zealand and Antarctica had a close geographic relationship on the eastern margin of Gondwana.
After having been influenced by proximity to the Permian ice sheet, during which New Zealand and Antarctica shared elements of the
Glossopteris
flora, the eastern margin of Gondwana entered into a phase of predominantly cool-temperate climates that lasted throughout the Triassic.
In the Jurassic, rotation of Gondwana had moved New Zealand and Antarctica into mid-latitudes and they experienced warm-temperate climates. These climatic conditions facilitated the dispersion of Tethyan marine faunas into the SW Pacific sector of eastern Gondwana. New Zealand and Antarctica shared many elements of the Tethyan marine faunas.
Starting in Middle Jurassic times, earth movements of the Rangitata Orogeny began to create considerable areas of land in the New Zealand region. Eventually, by Late Jurassic and Early Cretaceous times, a large landmass had been developed, extending northwards towards New Caledonia, eastwards to the Chatham Islands, westwards to the Lord Howe Rise and southwards to the edge of the Campbell Plateau. Creation of this landmass, and its associated land and marine links, together with the equable warm-temperate conditions then apparent over large areas of Gondwana, provided favourable conditions for the dispersal of Gondwana elements into New Zealand. Ancestral stocks of at least some of New Zealand’s archaic endemic terrestrial biota may have dispersed from eastern Gondwana into New Zealand at this time.
In the Early Cretaceous, land connections to eastern Gondwana became weakened by the onset of rifting along the future sites of the Tasman Sea and Southern Ocean. The eastern edge of Gondwana was rotated into high latitudes, and cool-temperate climates returned to New Zealand and Antarctica. Cool-temperate Austral marine faunas developed and were shared between New Zealand, Antarctica and southern South America. Land links between New Zealand and West Antarctica provided access for early angiosperms. However, all land links between New Zealand and Australia/Antarctica were broken after 85 Ma. From this time onwards the ancestral Tasman Sea and Southern Ocean became effective barriers to overland dispersal between eastern Gondwana and New Zealand. Subsequently, all terrestrial colonists had to arrive by either flying, swimming or floating. Many birds did so, but no terrestrial snakes and no mammals, except bats.
Although land connections had been broken in the Late Cretaceous, shallow-water marine links continued to exist between New Zealand and West Antarctica until the late Paleocene (the Weddellian Province). However, as New Zealand moved progressively northwards and the Southern Ocean widened, such southern links gave way in latest Paleocene and early Eocene times to northern (Australian and Malayo-Pacific) links.