Episode 86 – New Zealand

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In the South Pacific Ocean, there is a family of islands that have been isolated since the Cretaceous Period. Now and in the distant past, it’s been home to some of the most unique and fascinating ecosystems on Earth. This episode, we explore the history and the evolution of New Zealand.

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New Zealand

The country of New Zealand consists of two main islands surrounded by hundreds of smaller ones, located on a mostly sunken section of continental crust known as Zealandia. It sits in the center of what is known as the Water Hemisphere, the half of the globe that contains the highest percentage of water.

These islands host a variety of ecosystems, inhabited by an abundance of plants and animals that are found nowhere else in the world (they’re endemic to New Zealand). As we’ve discussed, evolution gets weird on islands, and this is no exception; New Zealand’s wildlife tends to be a bit strange.

Tuatara_Sphenodon_punctatus_standing_proud
Tuataras are New Zealand’s largest reptiles, reaching about 1.5 feet (half a meter) in length. They look like lizards, but are actually the only surviving members of the rhynchocephalians, a group that was successful and diverse in the early Mesozoic. Image from Michael Hamilton Digitaltrails / CC BY-SA 3.0
Cook_Strait_Giant_Weta_(5601688959)
New Zealand is home to more than 70 species (mostly endemic) of wētā, a group of flightless crickets known in the Southern Hemisphere. These include some of the largest insects in the world, with some reaching 2.5 ounces as adults. Image from Sid Mosdell from New Zealand / CC BY 2.0

Like many islands, New Zealand is missing a lot of diversity seen elsewhere. There are numerous species of lizards, but only geckos and skinks, and there are no native snakes or crocodilians at all. There are only four species of New Zealand frogs, all in the genus Leiopelma, a group that goes through the tadpole phase inside the egg and hatch as little froglets. The only mammals native to the region are two species of bats, while a diversity of birds (including many flightless species) have adapted to fill ecological roles we would expect to see from mammals.

Kiwi_bird_in_Christchurch,_New_Zealand,_2002-01-01
Kiwis are among the most famous New Zealand animals. These small birds are completely flightless, using their powerful legs and long beaks to search the dirt for insects. Unlike other birds, their nostrils are at the end of their beak, and they have an excellent sense of smell. Allie_Caulfield / CC BY 2.0
Parrots
New Zealand is home to a variety of parrots, including flightless kakapo (left), the world’s heaviest living parrot, and the intelligent mountain-dwelling kea (right), which are known to feed on carrion and even attack sheep. Left Image from Department of Conservation / CC BY 2.0, Right Image from Ltshears / CC BY-SA 3.0

Many of these native species have been pushed to the brink of extinction (or beyond) by the introduction of invasive species by humans.

History

Zealandia_topography
Today, Zealandia occupies a total area of 4,920,000 square kilometers (1,900,000 square miles). It forms a section of the Australian Plate and borders with the Pacific Plate. Image from World Data Center for Geophysics & Marine Geology (Boulder, CO), National Geophysical Data Center, NOAA / Public domain.

The rocky foundation of New Zealand had begun forming as far back as the Cambrian, and it spent most of its history as part of the southern supercontinent Gondwana, which also included Australia, Antarctica, Africa, and South America.

Gondwana began to come apart toward the end of the Mesozoic Era, and by 75 million years ago, Zealandia had split apart from the rest. For a while, some famous Mesozoic animals still persisted in the region, as evidenced by fragmentary fossils and trackways of dinosaurs and marine reptiles.

By 65 million years ago, New Zealand was fully isolated, allowing the evolution of unique varieties of plants and animals. During the Oligocene Period (34-23 million years ago), nearly all of Zealandia was underwater, but as the land rose again during the Miocene, we see some familiar ecosystems arise.

Fossils

The St. Bathans fossil deposit preserves an excellent record of early Miocene life on New Zealand, including the giant flightless parrot Heracles inexpectatus and the possibly flighted kiwi, Proapteryx, as well as some of the earliest moas, a group of giant flightless birds that served as primary ground herbivores and lived on New Zealand until the 1500s. This fossil site also preserves evidence of animals that no longer live on the islands, like mekosuchian crocodiles up to 10 feet (3 meters) long and at least one species of a very strange mammal that doesn’t belong to any living lineage.

Giant_moa
There were many species of moa, but the largest grew as large as 10 feet (3 meters) tall and weighed 550 pounds (250kg). Once thought to be close relatives of kiwis, the latest data suggest both groups of now-flightless birds arrived in New Zealand separately and became flightless independently. Image from Joseph Smit / Public domain

In the Pleistocene, we see the arrival of another group of famous giant birds: Haast’s eagles. These were the dominant predators on New Zealand for quite some time, growing as large as 30 lbs (15kg), with wingspans up to 8.5 feet (2.5 meters). These birds of prey were driven to extinction along with the moas by the 1500s.

Canterbury_Museum,_Christchurch_-_Joy_of_Museums_-_Haast's_Eagle
The size and shape of the wings of Haast’s eagles suggest they weren’t soaring while hunting, but instead would find a high perch in their wooded habitat and look for prey from there. Image form GordonMakryllos / CC BY-SA 4.0

If you’d like to learn more check out these links:
Kea – Mountain Parrot Documentary
How New Zealand’s Glaciers Shaped The Origin of the Kiwi Bird
Waimanu – 60-million year old penguins from New Zealand
Dead as the moa – oral traditions show that early Māori recognised extinction

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