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Emperor penguins are the largest penguins alive today.

Credit: Christopher Michel CC BY-2.0

Penguins come in many shapes and sizes, from little penguins all the way up to kings and emperors. But millions of years ago, penguins were even bigger, and studying these gigantic birds can teach us a lot about evolution.

Meet the giants

Right now, the largest penguins are emperor penguins. Standing 120 centimetres tall, they’re able to look many seven-year-old humans in the eye. Emperor penguins are also amazing swimmers, able to reach speeds of 15 kilometres per hour, which is as fast as some adult humans can run.

Giant penguins, including Kumimanu, lived in Aotearoa New Zealand around 60 million years ago.

Credit: Mark Witton

Yet emperor penguins are small compared to ancient penguins. Looking back 62 million years, only a few million years after dinosaurs went extinct, New Zealand teemed with penguin species. The Kumimanu, stood around 160 centimetres tall, as tall as many adult humans. But the biggest swimming birds ever, lived somewhere (and somewhen) else entirely.

Meet the plotopterids. Like penguins, they were aquatic birds that swam with their wings. They emerged around 35 million years ago in the northern hemisphere, and the largest species grew to around two metres tall. But they weren’t closely related to penguins. Their closest relatives were diving birds like cormorants, shags and boobies.

Surprising similarities

Plotopterids, such as these Copepteryx, looked a lot like penguins.

Credit: Mark Witton

Recently an international team compared bones from plotopterids and ancient penguins, and found plenty of similarities. Both families had long beaks with slit-like nostrils, similar chest and shoulder bones, and similar wings.

So why were these two birds so alike? Scientists believe that they lived similar lives, so they evolved similar features. This is a process called convergent evolution.

“These birds evolved in different hemispheres, millions of years apart, but from a distance you would be hard pressed to tell them apart,” says Dr Paul Scofield from Canterbury Museum in New Zealand. “Plotopterids looked like penguins, they swam like penguins, they probably ate like penguins – but they weren’t penguins.”

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