Researchers used brown and black chicken feathers for their study
March 6, 2014

Researchers Re-Examine Color In Fossil Feathers

April Flowers for - Your Universe Online

It has been proposed by paleontologists who study fossilized feathers that the shapes of certain microscopic structures found inside the feathers might tell us the color of the ancient birds. If these structures are melanosomes, that could be true. A new study, led by North Carolina State University, however, demonstrates that it is not yet possible to tell if the structures are melanosomes, or remnants of ancient bacteria.

Found inside the cells of feathers and other pigmented tissues of vertebrates, melanosomes are small, pigment-filled sacs that contain melanin. Melanin can give feathers colors ranging from brownish-red to gray to solid black. The sacs can be round or oblong in shape, and finding such structures in preserved feathers has led scientists to speculate about the physiology, habitats, coloration and lifestyles of the extinct animals — including dinosaurs — that once possessed them.

The difficulty lies in the fact that melanosomes are not the only round and oblong structures that might appear in fossilized feathers. The bacteria that drove the decomposition process of the animal's remains prior to fossilization are approximately the same shape and size as melanosomes. These bacterial remains would also be present in feathers during decay.

Whether or not these structures could be definitively identified as either melanosomes or bacteria intrigued Alison Moyer, a PhD candidate in paleontology at NC State. Moyer and her colleagues used brown and black chicken feathers, which are one of the closest living relatives to dinosaurs and ancient birds, and grew bacteria over them to replicate what is observed in the fossil record. Three different types of microscopy were used to examine the patterns of biofilm growth. These were compared to melanosomes inside of chicken feathers that had been sliced open. The final step was to compare both microbes and actual melanosomes to structures found in a fossilized feather from Gansus yumenensis — an avian dinosaur that lived approximately 120 million years ago — provided by the Gansu Geological Museum in Lanzhou, Gansu, China, and to published images of fossil "melanosomes" by others. Moyer didn't find answers, just more questions.

“These structures could be original to the bird, or they could be a biofilm which has grown over and degraded the feather – if the latter, they would also produce round or elongated structures that are not melanosomes,” Moyer says. “Melanosomes are embedded in keratin, which is a very tough protein, so they’re hard to see unless there’s been some degradation. But the bacteria are doing the degrading, and so that may be what we’re seeing, rather than the melanosome itself. It’s impossible to say with certainty what these structures are without more data, including fine scale chemical data.”

Moyer intends to continue her research by testing for the presence of keratin or bacteria within the fossils, using their molecular structures.

“The technology that we have available to us as paleontologists now is amazing, and will make it much easier to test all of the hypotheses we develop about these fossils,” Moyer says. “In the meantime, perhaps we can establish some basic criteria for identifying these structures as melanosomes, such as whether they’re found within the feather’s interior, or externally.”

Their findings were published online in the journal Scientific Reports.