Feathery Fossil Makeovers

Photo credit to Wikimedia Commons
Photo credit to Wikimedia Commons

By Karen Zusi
BU News Service

I vividly remember learning in elementary school that scientists didn’t actually know what color the dinosaurs were. Suddenly, I could fill in the dinosaur coloring pages with pink-and-purple polka dots or rainbow stripes and nobody could tell me I was wrong. With my art teacher lamenting our lack of realism in every class project, it was like coming up for a breath of fresh air.

I was a junior in high school by the time anyone got around to telling me that dinosaurs had feathers, too. At sixteen years old, I was the youngest member of my local bird club, and Richard Prum from Yale University came to a chapter meeting to discuss whether Tyrannosaurus rex were actually covered in downy plumage. (His answer at the time was “well, sort of”). The revelation felt like a betrayal, as I’d been drawing dinosaurs with scales my whole life—but I’d just gotten into birdwatching, and I also thought it was the coolest thing ever. Over the nine years since, scientists have actually been using fossils to determine the color of these dinosaur feathers, shedding light on six-year-olds’ drawings worldwide.

We already know how the plumage of modern birds gets its color—from pigments in the feather barbs and from the microstructure of the feather itself.  Scientists suspect that dinosaur feathers functioned similarly. The pigments fall into three groups: melanins, the most common, create colors ranging from black to brown to pale yellow; porphyrins produce pinks, reds, browns, and greens; and carotenoids, acquired from eating plants, produce reds, oranges, yellows, and olive-greens. The microscopic layout of a feather also affects its appearance, depending on how the feather reflects light. Blue and iridescent feather colorings are from this structure.

Of all these pigments, melanins best survive the process of fossilization. Pockets of melanin in feather cells, called melanosomes, show up in fossils as microscopic imprints. When looked at under a powerful microscope, the size, shape, and orientation of the imprints give clues about what the feathers may have looked like. So far, fossils can’t tell us about the carotenoids or the porphyrins, but melanin can show the pattern of darker colors.

The first inkling that fossils might contain information about ancient feather color came in 2008. Scientists knew that some bird-feather fossils had microscopic imprints, but thought the imprints came from bacteria. However, Yale PhD student Jakob Vinther published a paper suggesting that the imprints were actually melanosomes. The research group at Yale confirmed this discovery with another study in 2010, opening the door for predicting color in dinosaur feathers—which is what two groups of researchers in China did the same year.

A team led by Fucheng Zhang analyzed fossil remains of Sinosauropteryx from the Chinese Academy of Sciences in Beijing. They discovered a pattern of melanosomes suggesting rufous-colored tail stripes (the brownish-orange color on robins and bluebirds). A separate team led by Quanguo Li, working with Vinther and Prum, analyzed remains of Anchiornis huxleyi and saw that the dinosaur’s body might have been black or grey with a rufous crest and white-patterned wings.

Further breakthroughs came in the following years. In 2012, PhD candidate Ryan Carney at Brown University published a paper in Nature Communications with evidence that some of Archaeopteryx’s feathers may have been black, and Li published another 2012 paper about the Microraptor, a feathered dinosaur that may have been entirely glossy-black as well.

Scientists continue to research this topic, with groups starting to investigate how the process of fossilization affects what melanosomes look like.  In 2013, researchers noted that fossilization can alter the shape and placement of melanosomes, casting some doubt on the accuracy of previous color analyses. Ornithologists also continue to research the feathers of living birds to better understand their color patterns, which facilitates easier comparisons to fossilized remains.

Without a time machine and a camera, it’s impossible to truly verify theories of dinosaur appearance. But researchers are certainly approaching a clearer understanding than my six-year-old self with her pink-and-purple polka-dotted dinosaurs—and that’s pretty cool.

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