Evrim Yazgin
Cosmos science journalist
Some of New Zealand’s most iconic species may actually have relatively recently trekked over from Australia according a more than 2-decades-long palaeontological study.
Zealandia’s true ancients
Researchers have found that the truly ancient species of New Zealand are animals like the kākāpō, small wrens, bats and freshwater limpets. These lineages have been present since the ancient continent Zealandia “unzipped” from Gondwanaland between 85 and 65 million years ago.
Kiwi, moa and takahē – birds often associated with Aotearoa (the Māori-language name for New Zealand; pronounced au·tay·uh·row·uh) – arrived on Zealandia more recently.
The study – conducted by an international team including researchers from both sides of the Tasman – is published in the journal Geobios.
“23 years of digging at St Bathans has changed our idea about the age of the New Zealand fauna and the importance of some animals over others,” says co-author Paul Scofield, Senior Curator Natural History at Canterbury Museum in Christchurch on New Zealand’s South Island.
“For example, until now we thought that birds like kiwi and moa were among the oldest representatives of New Zealand fauna.”
Window into Miocene Aotearoa
St Bathans is a fossil site in Central Otago on the South Island. The researchers closely examined 9,000 bones from the site dating to about 20 million years ago during the early Miocene period (23–5.3 million years ago).
Among the St Bathans finds are creatures which were wiped out by dramatic climate cooling about 5 million years ago. These included a giant parrot nicknamed ‘Squawkzilla’, 2 unusual mammals, flamingos, a 3-metre crocodile, a large horned turtle and a giant bat.
“The St Bathans Fauna was deposited in a temperate–subtropical environment, with forests dominated by laurels,” co-author Vanesa De Pietri, a researcher at the University of Canterbury, tells Cosmos.
“There was a large lake (the Manuherikia Paleolake), which was estimated to have been 5,600km2 in area [about half the size of South Australia’s Lake Eyre], and this was the source of the sediments that preserve the St Bathans Fauna.”
“There are animal lineages that have a demonstrably longer presence in Aotearoa than others,” De Pietri adds. “We can infer how long a lineage has been present based on the fossil record, but also from evidence from molecular studies, which provide hypothetical dates for when lineages first appear.”
De Pietri notes that molecular studies suggest some animals made it to New Zealand before the Miocene, “but because sediments preserving land-dwelling vertebrates older than the St Bathans Fauna are unknown, we lack direct evidence”.
By 20 million years ago, Zealandia’s had its unique animals
First author Trevor Worty, an assistant professor at Flinders University in Adelaide, South Australia, says that the research helps understand the geographical distribution of animals millions of years ago.
“The research shows that many of the species that we thought of as iconic New Zealand natives – a classic example would be the takahē – are relatively recent blow-ins from Australia, arriving only a few million years ago,” Worthy explains.
New Zealand today boasts a unique assemblage of plants and animals – owing largely to its geographical isolation.
Worthy says his team’s findings show Zealandia’s unique groups of taxa were already present 20 million years ago.
“What we are seeing from 20 million years ago is that very few of the birds and other vertebrates are closely related to any Australian taxa.”
“There has been a debate in recent years concerning how much of Zealandia was above water at the end of the Oligocene (25 million years ago),” Worthy says. “Now it is agreed a fairly large island persisted during this period of high sea level and on it was a diverse variety of animals and plants.”
“The St Bathans Fauna shows what was living on Zealandia only some 5 million years after this and that these animals include all the iconic ancient animals recognised in the fauna people encountered. It shows no such animals dispersed to Zealandia in the last 20–16 million years.”
Of today’s iconic New Zealand animals, very few have arrived since. The ancestors of the large, flightless takahē – related to the Australasian swamphen – would have flown over from Australia just 1 million years ago according to the research.
