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Giant Penguin-Like Seabirds Lived in Northern Hemisphere About 30 Million Years Ago

Paleontologists have discovered striking similarities between the fossilized bones of giant penguins that lived 62 million years ago in what is now New Zealand and those of the plotopterids, a group of flightless seabirds that lived in North America and Japan between 37 and 25 million years ago.

A group of Copepteryx, plotopterid birds that lived in Japan between 28.4 and 23 million years ago. Image credit: Mark Witton.

A group of Copepteryx, plotopterid birds that lived in Japan between 28.4 and 23 million years ago. Image credit: Mark Witton.

Plotopterids (family Plotopteridae) are extinct, flightless and wing-propelled diving birds that combine a striking mosaic of features characteristic for true penguins and pelecaniform birds like gannets, boobies, cormorants, and anhingas.

The wing of plotopterids is remarkably similar to the flipper of penguins, to which it shows numerous parallels.

Plotopterids developed in the northern hemisphere much later than penguins, with the first species appearing between 37 and 34 million years ago. Their fossils have been found at a number of sites in the United States (California, Oregon, and Washington), Canada (British Columbia) and Japan.

Unlike penguins, which have survived into the modern era, the last plotopterid species became extinct around 25 million years ago.

In a new study, Dr. Gerald Mayr from the Senckenberg Research Institute and Natural History Museum and his colleagues from the United States and New Zealand compared the fossilized remains of plotopterids with fossil specimens from three species of giant penguins — Waimanu, Muriwaimanu, and Sequiwaimanu — and identified previously unrecognized similarities and differences.

The researchers found plotopterids and the ancient penguins had similar long beaks with slit-like nostrils, similar chest and shoulder bones, and similar wings.

These similarities suggest both groups of birds were strong swimmers that used their wings to propel them deep underwater in search of food.

Some species of both groups could grow to huge sizes. The largest known plotopterids were over 2 m long, while some of the giant penguins were up to 1.6 m tall.

“What’s remarkable about all this is that plotopterids and ancient penguins evolved these shared features independently,” said Dr. Vanesa De Pietri, Curator of Natural History at the Canterbury Museum.

“This is an example of what we call convergent evolution, when distantly related organisms develop similar morphological traits under similar environmental conditions.”

“Some large plotopterid species would have looked very similar to the ancient penguins,” said Dr. Paul Scofield, Curator of Natural History at the Canterbury Museum.

“These birds evolved in different hemispheres, millions of years apart, but from a distance you would be hard pressed to tell them apart.”

“Plotopterids looked like penguins, they swam like penguins, they probably ate like penguins — but they weren’t penguins.”

The parallels in the evolution of these bird groups hint at an explanation for why birds developed the ability to swim with their wings.

“Wing-propelled diving is quite rare among birds; most swimming birds use their feet,” Dr. Mayr said.

“We think both penguins and plotodopterids had flying ancestors that would plunge from the air into the water in search of food.”

“Over time these ancestor species got better at swimming and worse at flying.”

A paper on the findings is published in the Journal of Zoological Systematics and Evolutionary Research.

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Gerald Mayr et al. Comparative osteology of the penguin-like mid-Cenozoic Plotopteridae and the earliest true fossil penguins, with comments on the origins of wing-propelled diving. Journal of Zoological Systematics and Evolutionary Research, published online June 29, 2020; doi: 10.1111/jzs.12400

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