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How the penguin changed its feathers

A 36 million-year-old fossil found in Peru suggests that the feathers of ancient giant penguins followed a different color scheme — and may not have been as hardy as they are today.

Instead of sporting the classic tuxedo look of modern penguins, the fossil species known as Inkayacu paracasensis ("Water King of Paracas" in the Quechua language) had reddish brown and gray feathers, paleontologists report in a research paper published online today by the journal Science. The creature was nearly 5 feet tall, which outdoes the height of today's largest living penguin, the Emperor.

"Before this fossil, we had no idea about the feathers, colors and flipper shapes of ancient penguins," lead author Julia Clarke, a paleontologist at the University of Texas at Austin, said in a news release. "We had questions, and this was our first chance to start answering them."

The fossil was discovered by a Peruvian student, Ali Altamirano, in the Paracas National Reserve on the Peruvian coast south of Lima. When the researchers noticed that there was scaly soft tissue preserved on an exposed foot, they nicknamed the specimen "Pedro," after a sleazy, scaly character from a Colombian soap opera.

The fossil preserved not only the shapes of Pedro's flippers and the feathers, but also the fine patterns of color-producing nanostructures known as melanosomes. Those patterns could be compared with a vast database of melanosome structures for living birds. The comparisons are what led Clarke and her colleagues to conclude that Pedro's color scheme was gray and red, because melanosomes with those colors matched the fossilized structures best.

The shapes of the feathers and the flippers were very similar to what is seen in penguins today. But the patterns of the fossilized melanosomes had less in common with today's penguins and more in common with other types of aquatic birds. Modern-day penguins have giant melanosomes that are broader than the ones that were found in the giant penguin fossil. In fact, today's penguins have bigger melanosomes than the ones found in all the other living bird species that were surveyed. What's more, a modern penguin's melanosomes are grouped into clusters like bunches of grapes.

This information led the researchers to put together the evolutionary story of how the penguin changed its feathers.

They theorize that penguins initially adapted to their aquatic environment by developing strong, streamlined feathers that were stacked on top of each other to create stiff, narrow flippers. Then, long after Pedro bit the dust, the melanosomes took on larger sizes and a clustered arrangement. But why would the melanosomes change?

It turns out that the coloring agent contained in the melanosomes, melanin, makes the feathers more resistant to wear and fracturing. Birds with bigger melanosomes would find it easier to keep their feathers in shape during those long, hard days of swimming.

The color change itself might have been a side effect of the shift in melanosome structure, or it might have had more to do with a protective response to relatively recent predators as leopard seals. Maybe gray and red made the penguin stand out too much, compared with the more austere black-and-white scheme.

"Insights into the color of extinct organisms can reveal clues to their ecology and behavior," said Yale University's Jakob Vinther, one of the research paper's co-authors. "But most of all, I think it is simply just cool to get a look at the color of a remarkable extinct organism, such as a giant fossil penguin."

Update for 4 p.m. ET: As you can imagine, a lot of people are talking (and writing) about this story. Over at LiveScience, Stephanie Pappas quotes Gerald Mayr, a paleornithologist at the Senckenberg Museum of Natural History, as saying that the action of hydrodynamic forces on feathers may not totally explain why penguins evolved to have bigger melanosomes. He pointed out that a penguin's white feathers containe no melanosomes and yet would be subject to the same forces as the black ones. "The main question certainly is, if not due to hydrodynamic forces, why do penguins have such strange melanosomes?" he said.

Ker Than's piece for National Geographic explains the modern penguin's camouflage: A swimming predator looking up from below would see the bird's white belly blending in with the sky, while the bird's black back would blend in with the dark watery depths when viewed from above. At Not Exactly Rocket Science, Ed Yong puts the Water King in context alongside other ancient penguins discovered in Paracas Park. Yong also links in turn to March of the Fossil Penguins, a blog which would have to be the definitive source on this subject. The blog's author? None other than Daniel Ksepka, one of the co-authors of the Science paper.

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In addition to Clark, Altamirano, Vinther and Ksepka, the authors of "Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers" include Rodolfo Salas-Gismondi, Matthew Shawkey, Liliana D'Alba, Thomas DeVries and Patrice Baby. The paper will appear later in Science's print edition. The National Geographic Society and the National Science Foundation provided funding for the research.

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