Natural history of New Zealand
Since this separation, the New Zealand landscape has evolved in physical isolation, although much of its current biota has more recent connections with species on other landmasses.
Most of the present biota of New Zealand has post-Gondwanan connections to species on other landmasses, but does include a few descendants of Gondwanan lineages, such as the Saint Bathans mammal.
[5] Several elements of the Gondwana biota are present in New Zealand today: predominantly plants, such as the podocarps and the southern beeches, but also distinctive insects, birds, frogs and the tuatara.
It has been suggested that water covered all of it,[7] but the consensus is that low-lying islands remained, perhaps a quarter of the modern land area of New Zealand.
[12] As Zealandia had rifted away at this time it explains the lack of ground-dwelling marsupials and placental mammals in New Zealand's fossil record.
Dinosaurs continued to prosper but, as the angiosperms diversified, conifers, bennettitaleans and pentoxylaleans disappeared from Gondwana c. 115 Ma together with the specialised herbivorous ornithischians, whilst generalist browsers, such as several families of sauropodomorph Saurischia, prevailed.
[13] Gondwanatheria is an extinct group of non-therian mammals with a Gondwanan distribution (South America, Africa, Madagascar, India, and Antarctica) during the Late Cretaceous and Palaeogene.
The Late Cretaceous pollen record shows that some types of flora evolved across Gondwana, while others originated in Antarctica and spread to Australia.
The laurel forests of Australia, New Caledonia, and New Zealand have a number of species related to those of the laurissilva of Valdivia, through the connection of the Antarctic flora.
[22] At the start of the Paleocene New Zealand's biota was recovering from the extinction of dinosaurs, and the species that survived were expanding into the empty niches.
This led to the formation of a subduction arc with active volcanism forming islands north and west of present New Zealand.
[33][34][35] However, 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.
[5] 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.
[8] 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.
Foulden Maar, a maar-diatreme volcano in Otago, preserved a high diversity of freshwater fish, arthropods, plants and fungi at a lake 23 Ma.
[37] The fossil evidence derived from pollen and spores suggests a warm temperate or sub-tropical rain forest with canopy trees, with an understorey of shrubs, ferns and on the margins pioneer species.
Climatically, the area resembled modern-day south-eastern Queensland, a humid sub-tropical zone with species that no longer occur in the New Zealand flora.
Much of the Southern Alps and Fiordland were glaciated and much of the rest of New Zealand was covered in grass or shrubs, due to the cold and dry climate.
[47][48] These vast tracks of exposed land with little vegetation cover increased wind erosion and the deposition of loess (windblown dust).
