page_title: Natural history of New Zealand
section_title: New Zealand's shallow seas (Oligocene 33.9 to 23 Ma)
hierarchical_section_title: Natural history of New Zealand / New Zealand's shallow seas (Oligocene 33.9 to 23 Ma)
caption_attribution_description: English: New Zealand before the activation of the Alpine Fault (30 ma)
context_page_description: The natural history of New Zealand began when the landmass Zealandia broke away from the supercontinent Gondwana in the Cretaceous period. Before this time, Zealandia shared its past with Australia and Antarctica. Since this separation, the New Zealand biota and landscape has evolved in near-isolation. The exclusively natural history of the country ended in about 1300 AD, when humans first settled, and the country's environmental history began. The period from 1300 AD to today coincides with the extinction of many of New Zealand's unique species that had evolved there.
  The break-up of Gondwana left the resulting continents, including Zealandia, with a shared ecology. Zealandia began to move away from the part of Gondwana which would become Australia and Antarctica approximately 85 million years ago. By about 70 Ma, the break up was complete. Zealandia has been moving northwards ever since, changing both in relief and climate. The present biota of New Zealand does include descendants of Gondwanan lineages, but has lost many others, such as the Saint Bathans mammal, and has received many immigrant populations.
context_section_description: From the early Oligocene, at maximum submersion of the Zealandia landmass, almost all New Zealand's rocks are marine. Oligocene terrestrial sediments are few, scattered, and not well-dated. It has been suggested that at some point, Zealandia was entirely underwater, and consequently all land biota would be descended from later immigrants.
  Molecular estimates of divergence times between 248 extant New Zealand lineages and their closest relatives elsewhere follow approximately a smooth exponential over the last 50 million years or more. Some 74 of these lineages appear to have survived the Oligocene in New Zealand. There is no evidence for a deficit of pre-Oligocene lineages, nor an excess of lineages arriving just afterwards. This strongly suggests that New Zealand was never submerged completely. Although there is no obvious peak of lineage extinction in the Oligocene, the limited diversity of mitochondrial DNA in kiwis, moas, and New Zealand wrens indicate that all three lineages underwent a genetic bottleneck (small effective populations) roughly coinciding with the maximum submersion; New Zealand at this time probably consisted of low-lying islands with a limited diversity of habitats.
  Significant uplift occurred by the mid-Oligocene (~32–29 Ma) in the modern Canterbury Basin, where palaeochannels eroded through the early Oligocene Amuri Limestone lead eastwards to the present Bounty Trough.
  The North and South island have been separate for most of the last 30 million years allowing for the development of separate sub species.
caption: New Zealand before the activation of the Alpine Fault (30 Ma)
exif: {}