Modern penguins thrive in cold climates. So why didn't the New Zealand penguin survive? (Photo: Richard McManus via Getty Images)
Three million years ago, an extinct relative of today's large penguins, the emperor and king penguins, lived in Aotearoa, New Zealand.
We know this because our new study describes a spectacular fossilised skull of a large penguin found on the Taranaki coast.
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However, compared to emperor penguins, the Taranaki penguin had a much stronger and longer bill. It was likely more similar to the king penguin (Aptenodytes patagonicus), only much larger.
At that time, the world was warmer than it is today. But when the climate cooled, this penguin disappeared.
We argue that cold was not the cause, as New Zealand's rockhopper and little penguins survived the same changes and survived. Great penguins migrated south and today inhabit the icy expanses of Antarctica. So what led to the extinction of their ancient relative?
The fossil skull (top) of the extinct great penguin in its presumed original form, compared with the skulls of the king penguin (centre) and emperor penguin (bottom).
The sediments that now form the coastal cliffs of South Taranaki were deposited during a period when global temperatures were approximately 3°C warmer than pre-industrial levels. Fossil remains from this period are changing our understanding of how biodiversity might respond to rising temperatures.
For example, Aotearoa was home to boxfish and monk seals, both of which are still (sub)tropical species today. In a strange contradiction, in ancient New Zealand, they coexisted with giant penguins, which are now found only in much colder climates.
The northernmost breeding colonies of king penguins are currently located around 46.1° south latitude on the subantarctic Crozet Islands, where seawater temperatures reach 3–10°C. From there, the temperature only gets colder as one moves toward the higher latitudes where emperor penguins live.
Today, the great penguin's habitat is limited to the subantarctic islands and the coast of Antarctica (map left). However, ancient New Zealand was home to an extinct species of great penguin approximately three million years ago, during a period in Earth's history known as the Middle Piacenzian Warm.
Three million years ago, the range of Aotearoa's great penguins extended north of 40.5°S, where South Taranaki was then located. They foraged in waters with a temperature of 20°C, significantly warmer than their modern relatives.
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This blissful existence ended with the Pleistocene ice ages approximately 2.58 million years ago. Glacier extent and sea levels fluctuated with temperature fluctuations and eventually dropped. But why did such cooling lead to the extinction of New Zealand's giant penguins, which today thrive in polar conditions?
Giant aerial predators
Fossil evidence for giant penguins in Aotearoa is limited, and the exact causes of their extinction remain unclear. However, their very presence suggests that sea surface temperatures limited their capabilities to a lesser extent than previously thought. Another mechanism must be at play.
About 500 years ago, Aotearoa was the hunting grounds of the giant Haast's eagle and the enormous Forbes's harrier. These were large birds of prey whose diet included large birds such as moas. Their ancestors arrived from Australia within the last three million years.
An artist's conception of an extinct large penguin that lived in New Zealand about three million years ago.
Judging by what we observe in modern great penguins, the Taranaki penguin almost certainly formed large, open colonies along the coast. These would have been easy prey for a giant eagle or harrier hunting from the air.
In contrast, the smaller penguins still found in Aotearoa are more secretive when breeding. They nest in burrows, natural crevices, and dense vegetation, and typically cross beaches at night, which may have helped them avoid aerial predators.
However, terrestrial predation is only one hypothesis explaining why these penguins became extinct in the region while others survived. Other possibilities include changes in the marine environment.
We know that reduced food availability can have devastating consequences for penguins, but it's difficult to understand why this is particularly true for great penguins.
Importantly, our study provides new insights into the habitat tolerance of great penguins. King and emperor penguins are now able to tolerate temperatures 20°C higher than their typical foraging ranges.
Three million years ago, their relative experienced similar warmth. As the world continues to warm, we must remember that a species' range can shift depending on circumstances.
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Aotearoa's marine ecosystem will be home to many new species, making research into the last warm period more important than ever before.
We would like to acknowledge our study co-author Dan Ksepka of the Bruce Museum, Kerr Sharp-Young for discovering the fossil, and Ngāti Ruanui and Ngāruahine for their support in collecting and examining fossils from their rohe.
This edited article is republished from The Conversation under a Creative Commons license. Read the original article.
Daniel Thomas, Honorary Academician (Faculty of Biological Sciences), University of Auckland, Waipapa Taumata Rau
Daniel Thomas received his PhD in geology and zoology from the University of Otago in 2009, where his research focused on penguin evolution. He completed a postdoctoral fellowship at the University of Cape Town and worked at the Smithsonian Institution's National Museum of Natural History, where he studied fossils and the origins of feather coloration. Thomas later taught zoology at Massey University in Auckland and is currently an Honorary Academician in the School of Biological Sciences at the University of Auckland.
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