Forest Vines to Snow Tussocks: The Story of New Zealand Plants
Tertiary New Zealand
Tertiary New Zealand15, 204, 205, 206
Mountains were raised in the New Zealand crustal complex (Rangitata orogeny) in the late Jurassic and early Cretaceous when it was still part of Gondwana. By the late Cretaceous, when separation of New Zealand from Gondwana began, it is believed the mountains had been largely eroded, so the physical background to most of the Tertiary fossil record we are about to consider is one of a low lying peneplain with strongly oceanic climates.
During the Paleocene, conifers of the family Podocarpaceae were dominant and Nothofagus of all three groups was fairly rare. Proteaceae were quite common and, as in Australia, Anacolosa appeared as well as a number of palms including probable Nipa. Casuarina also appeared and remained a significant element for most of the Tertiary. Casuarina no longer occurs in New Zealand as a native genus, but fossil pollen considered to be Casuarina had been known for some time. The recent discovery of impressions of the distinctive cone-like fruits of Casuarina and the related genus Gymnostoma has confirmed the presence of the family in New Zealand.207 The Myrtaceae also appear for the first time in the Paleocene with pollen referable to both Leptospermum and Metrosideros having been identified.
In the Eocene the podocarps declined in importance, although Phyllocladus is recorded for the first time. Nothofagus became dominant, firstly the fusca group and latterly the brassii group. Cupania and Bombax appeared, rather later than in Australia, along with a number of new page 246proteaceous genera and Freycinetia, Astelia, Quintinia, possibly Phormium, and the family Araliaceae (includes Pseudopanax). A genus now extinct in New Zealand, Ilex (which includes the holly), is also first recorded in the Eocene. Cooling at the end of the Eocene may have been the reason for the extinction of Anacolosa, Nipa and a number of Proteaceae.
During the Oligocene, New Zealand reached its present latitudes and also suffered its greatest reduction in area as a result of sea encroachment. The cooler climate of the late Eocene seems to have continued into the Oligocene, perhaps partly due in New Zealand's case to the development of cooler westerly winds and currents following the separation of Australia and Antarctica. The forests were dominated by the Nothofagus brassi group, although the N. fusca group, Casuarina, Myrtaceae, Palmae and Podocarpaceae were also prominent. Among genera to first appear in this period are Weinmannia, Elaeocarpus, Myrsine, Fuchsia, Coprosma, Laurelia and Epilobium.
The Compositae (daisy family) made its first appearance in the late Oligocene.
Warmer climates prevailed in the early Miocene and the land began to rise. Swampy areas were common and surrounding them were dense floristically rich forests. Many of the species cannot be identified with modern plants, but several Nothofagus brassii group species were common together with Myrtaceae (possibly including Eucalyptus), Casuarina, Podocarpaceae and tree ferns. Palms also were common and included a small fruited species of coconut in the northern North Island — Cocos zeylanica (Fig. 124). Among genera recorded for the first time are: Cordyline, Ripogonum, Dysoxylum, Alectryon, Macropiper, Pittosporum, Muehlenbeckia and Melicytus. An interesting incomer is Acacia, no longer present in New Zealand.
Figure 124 Two fossil coconuts of the extinct Cocos zeylanica. The larger of the two nuts is only about 4 cm across. The fossils are associated with a coal seam of Miocene Age at Cooper's Beach in the far north of the North Island. The coal seam dips below the sea and the small coconuts are washed onto the beach from time to time. Photo: J. E. Casey.
During the Pleistocene the climate deteriorated greatly with a succession of long glacials and shorter interglacials. The last species of the Nothofagus brassii group disappeared together with Microstrobus and Microcachrys (now restricted to Australia) of the Podocarpaceae, Casuarina, (?) Eucalyptus, Acacia and all Proteaceae except two species, namely Knightia excelsa and Toronia toru. With each glacial the alpine vegetation expanded and diversified; with each interglacial the forests expanded from refugia (albeit reduced in diversity) to largely reclothe the landscape.