natural history - Auckland Museum

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natural history background notes | origins gallery crust stretched and thinned and the land sank. From considerable continental beginnings, New Zealand became an archipelago of small swampy low-lying islands. As the land area reduced, species that had evolved here faced advancing waters and destruction of habitats, creating a biotic bottleneck. The original Gondwanan flora and fauna was considerably reduced. Later the survivors diversified and new species evolved. Wrens, moa and giant weta were all affected. Some modern birds are probably descendants of a single surviving species. Gondwana New Zealand did not remain a small archipelago for long. About 25 million years ago, a plate boundary started to develop through New Zealand between the Australian and Pacific plates. The collision between these two plates has pushed up our mountain ranges within the last six million years. Sediments from the continuous erosion of mountains has extended our coastlines to create new land. TIMELINE Climate Change and the Ice Ages In the course of its history, New Zealand has changed many times in both location and climate from subtropical to subantarctic. All have had a great influence on its plants and animals. The climate changes are mediated by tectonic movements as well as more cosmic events. The current distribution of many indigenous animals is a legacy of the Pleistocene glaciations which ended some 10,000 years ago. During the last 64 million years there has been a global trend towards a cooler climate. In the Paleocene and Eocene the oceans were sluggish and Antarctica had no ice cap. During the Oligocene the movement of Australia away from Antarctica and the opening of the Drake Passage at the bottom of South America allowed the formation of a cold circumpolar current around Antarctica. This thermally isolated Antarctica, allowing an ice cap to form. There was a warming trend in the late Oligocene-Middle Miocene. The drop in temperature at the end of the Miocene 6
natural history background notes | origins gallery is due to the isolation and evaporation of the Mediterranean Sea. This event decreased the salinity of the oceans, allowing them to freeze at higher temperatures. The polar ice cap increased in size. The uplift of the Himalayas drove drier winds over Northern Africa, and affected rainfall in Asia. Three million years ago, North and South America joined, terminating warm currents around the equator and promoting the warm Gulf Stream in the North Atlantic. The Gulf Stream is responsible for snowfall on the North Pole, creating the Northern Hemisphere Ice Cap. a touch of the tropics 25–14 million years ago warm currents from tropical seas washed New Zealand shores and the climate was subtropical. Coconuts, corals and cone shells flourished. Warmth-loving plants established. Some died out later when the climate cooled again, others adapted and stayed. the Ice ages Earth’s climate has swung between warm and cold about 50 times in the last 2.6 million years. During particularly cold periods called Ice Ages or Glaciations, ice sheets grew on the continents causing sea levels 2 4 The hard parts may be buried by soil, mud, or sand, which protects them from further decay or damage. Forces deep within the earth may fold or tilt the rock and push some of them up to form land and mountains. to drop up to 120m. The frequency and regularity of the oscillations tell us that it is changes in Earth’s orbit that controls the amount of heat reaching Earth’s surface. Ice age climate had a large impact on New Zealand’s flora. This included the expansion of grasslands in both islands and the growth of alpine shrubs and herbs at much lower elevations than today. WHat are FossIls? Most fossils are the preserved hard parts of plants or animals, such as wood, shells, bones and teeth. Less common are the traces of soft parts like leaves and soft tissues. Some fossils show where an animal has been, such as footprints and worm trails. Fossils are found in sedimentary rocks in many parts of New Zealand, from sea level to mountain tops. 1 3 5 When an animal or plant dies its soft parts are usually eaten by scavengers or decay rapidly. Many layers of sediment may accumulate on top. Eventually, they harden into rock. We find fossils in cliffs and road cuttings where natural erosion or bulldozers have exposed layers of rock. 7
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natural history - Auckland Museum

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