New Zealand has almost no native mammals; its larger animal life is dominated by birds, lizards, frogs, wētā and land snails. Many of these species and groups of species have unusual characteristics.
New Zealand’s plants and animals have similarities to those living on nearby southern land masses, which were once joined as the Gondwana supercontinent. For years scientists thought that many of New Zealand's life forms were primitive survivors, isolated since the country broke away from Gondwana about 85 million years ago. But new research has shown that many of today’s native species are more recent arrivals that came to New Zealand over large stretches of ocean.
Origins and arrival
There are three key questions about New Zealand’s plants and animals:
- Where did their ancestors come from?
- How did they get to New Zealand?
- Are they different from plants and animals elsewhere, and if so, why?
To answer these, we need to look at evolution, dispersal and extinction – the main processes that control biodiversity. These in turn are influenced by factors such as land area, soil, climate, isolation, tectonics and catastrophic events. The development of New Zealand’s plants and animals is strongly connected to the country's geological and climatic history.
Once were mammals?
Until recently, evidence that early mammals (monotremes) lived in New Zealand was purely circumstantial. Dinosaurs and mammals lived alongside each other in Gondwana 85 million years ago. Dinosaur fossils 65–75 million years old have been found in New Zealand, so scientists think that mammals may have also been present. A primitive mammal bone between 16 and 19 million years old was recently found in Central Otago, spectacularly confirming this hypothesis.
About 120 million years ago the land that was to become New Zealand was still part of Gondwana. It was mountainous, and lay within the Antarctic Circle (latitude 66° south). There was complete darkness for three months in winter and continuous sunlight during the short summers. The climate was cool but not cold. There were forests of tall conifers, including podocarps (relatives of the modern kauri, Agathis australis), Wollemi pine (Wollemia nobilis), and conifer relatives – ginkgo and groups that are now extinct. These trees grew above horsetails, mosses, liverworts and hornworts.
By 100 million years ago there were early flowering plants in the part of Gondwana that was to become New Zealand. A diverse forest developed – largely deciduous flowering trees and conifers. Not much is known about the land animals of the Cretaceous period (146–65 million years ago), but there were dinosaurs, birds, tuatara (Sphenodon) and geckos. It is likely that there were also freshwater crocodilians and early mammals (monotremes).