The late Eocene giant penguin Icadyptes salasi (right) and the middle Eocene Perudyptes devriesi (left) are shown to scale with a Humbolt Penguin, the only living member of the group found in Peru today.

Credit: Kristin Lamm

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ADELAIDE: Giant penguins, almost as tall as a human, once waddled in tropical Peru, say the discoverers of a fossil that overturns established theories about the evolution of the seabirds.

Palaeontologists unearthed the fossil remains of two new species of penguin in southern Peru in 2005. They are the oldest complete penguin fossils ever discovered in South America, the international experts reveal today in the Proceedings of the National Academy of Sciences journal.

These species are tens of millions of years older than expected and challenge the assumption that penguins are specifically cold-adapted birds. At over one and half metres tall, 36-million-year-old Icadyptes salasi is also the most complete large penguin fossil ever found. The species had a beak almost 18 cm long, which the researchers believe it used to spear fish.

The second new species Perudyptes devriesi, stood around 60 cm tall, comparable in size to a modern King Penguin, and lived 42 million years ago during the middle Eocene period.

Northwards expansion

“These fossils now indicates that penguins reached low latitude regions more than 30 million years prior to our previous estimates,” said lead author Julia Clarke from the North Carolina State University in Raleigh.

Experts had previously predicted that penguin populations expanded northwards from Antarctica and New Zealand after the global climate cooled at the end of the Eocene period 33 million years ago. Other studies also suggested they did not reach more temperate southern latitudes, such as Peru, until about four to eight million years ago.

“We tend to think of penguins as being cold-adapted species,” said Clarke, “even the small penguins in equatorial regions today”. However, the newly discovered penguins lived during the Eocene era, a period when the Earth's climate was at its warmest in the last 65 million years.

“By indicating that penguins reached nearly the extremes of their present day range during a much warmer Earth, we show that major global cooling was not necessary for at least early penguins to invade equatorial regions,” she said.

Penguin diversity

Finding giant penguins in Peru also contradicts a theory that penguins have larger body sizes in the increasingly cool environments closer to the South Pole. “Our findings indicate that higher latitude was not correlated with larger body size in early penguins,” said Clarke. “Indeed, the evidence supports nearly as great a diversity in penguin body sizes and species diversity near the poles, as in low latitude Peru 42 million years ago.”

"[The new species] probably reached twice the body mass of the largest living penguin, the Emperor penguin, so would have weighed around 55 to 60 kg, and maybe stood as high as a person's shoulder,” commented Ewan Fordyce, a palaeobiologist from the University of Otago in New Zealand.

“These new records allow Clarke's team to produce a new evolutionary history, of penguins,” said Fordyce, which he describes as “a fertile field for research”.