The study of plant and animal fossils has thrown light on the overseas relationships of the past life of New Zealand and has also given some idea of past climates. Cambrian and Ordovician faunas are virtually cosmopolitan in their affinities, but those of the Cambrian are close to those of Queensland, Manchuria, and the Baltic, and those of the Ordovician, to Victoria. Close relationship to Eastern Australia is also shown by the Devonian faunas, but again with cosmopolitan (Europe, North America) elements. Two definite faunas characterise the Permian – a Lower Permian fauna of brachiopods, pelecypods, and solitary corals, closely related to South-East Australia and, to a lesser extent, South Africa, South America, and India; and an Upper Permian warm-water fauna of fusulinid Foraminifera and reef corals with Indo-Pacific affinities. In the Triassic and Lower Jurassic, many brachiopods and pelecypods are confined to New Zealand or occur elsewhere only in New Caledonia; at this time the two countries were evidently isolated from the remainder of the Indo-Pacific. On the other hand, during the same time the ammonites, which probably lived in the surface waters, and pterioid pelecypods, such as Daonella, Halobia, Monotis and Rhaetavicula, which probably had pelagic larvae, were able to migrate freely, and cosmopolitan forms in these groups are found in New Zealand. The Middle Jurassic is characterised by the arrival of another pterioid pelecypod (Meleagrinella) and other pelecypods and gastropods from Indo-Pacific countries. Indo-Pacific affinities also persist into the Upper Jurassic. Climatically, in the Triassic and Jurassic New Zealand probably lay in the warm temperate zone. The Lower Cretaceous is represented by ammonites and some pelecypods of European affinities, other pelecypods of Southern Hemisphere affinities, and belemnites of Australasian affinities. The Upper Cretaceous faunas, in contrast, show strong southern (for example, South American) affinities. Cretaceous climate was probably temperate or warm temperate. Distinct South American affinities are continued into the lowermost Tertiary molluscan faunas, but accompanied by Indo-Pacific, Australasian, and endemic elements. These latter three elements are also found in the faunas of the remainder of the Tertiary and in the Quaternary. Throughout the Tertiary, temperatures in the New Zealand region were temperate or marginal tropical at best (Lower Miocene of Northland). The Pleistocene history of New Zealand is dominated by successive periods of cooling, which caused the extinction of warm-water forms and allowed the incoming of southern cool-water forms, although Indo-Pacific and Australian elements have continued to colonise.
by Graeme Roy Stevens, M.SC.(N.Z.), PH.D.(CANTAB.), Paleontologist, New Zealand Geological Survey, Lower Hutt.