114 The Geological History of New Zealand

Key Idea: New Zealand's geological history and early isolation from other land masses has played a significant role in the evolution of New Zealand's unique flora and fauna. New Zealand became isolated from other land masses around 65 mya when the land mass that became New Zealand split away from Gondwana (below). The isolation resulted in the evolution of a unique array of organisms. With the exception of three native bat species (one extinct), no land mammals were present and niches occupied by mammals elsewhere in the world were, in New Zealand, filled by birds and insects. The geologic activity of New Zealand over its history has provided ample opportunities for speciation of these taxa.

The rise and fall of New Zealand

New Zealand has had a varied geological history, rising from below the sea, becoming half the size of Australia, and sinking to almost nothing before rising again to form high snow covered mountains. The New Zealand landmass is the highest point of a much greater submerged microcontinent known as Zealandia. The rise and fall of Zealandia allowed the organisms present to colonise new landscapes, before retreating to scattered islands. Large scale changes to the sea level (more than 100 m) during glacials has contributed to this fragmentation, periodically joining and separating the islands.

Timeline

150-100 mya

New Zealand is joined to the supercontinent Gondwana. Mammals have not yet diversified, dinosaurs still rule. Birds are evolving. Ancient plants including podocarps spread to ancestral New Zealand.

Present day

New Zealand is separated into three main islands and numerous small ones. Geological activity still continues, producing a variety of landscapes including snow fields, high rainfall differences between east and west, and low land plains.

2 mya to 0.5 mya

New Zealand assumes roughly its present shape. Changes in sea level during glacials connect the islands. Kakariki arrive and diversify.

70 mya

Plate boundary forms and Tasman sea begins to open. Dinosaurs still predominate and mammals are yet to spread widely. New Zealand is well forested with many available niches. Its most ancient organisms are present including geckos, frogs, tuatara, and snails.

40 mya

Erosion reduces New Zealand to less than half its previous size.

5 mya

The Kaikoura Orogeny begins, uplifting the Southern Alps, producing the first alpine environment in 50 million years. Many plants and animals move into the vacant niches including cicada, kea, and buttercups.

25 mya

New Zealand land mass has eroded to its smallest size (known as the Oligocene Drowning). Many small islands give opportunities for speciation, e.g. geckos and snails.

1. How did each of the following geological events provide an opportunity for speciation:

(a) New Zealand separates from Gondwana:

(b) The Oligocene Drowning:

(c) Kaikoura Orogeny: