X-ray fluorescence maps of zinc, calcium, and benzo-sulfur in a kestrel feather. (Image: SLAC National Accelerator Laboratory)

Textbook illustrations and museum dioramas could soon be even more accurate in their depiction of the rich colors of long-extinct animals like dinosaurs. An international team of scientists used advanced X-ray imaging techniques to map out elements related to pigmentation in modern birds of prey, which they will use to reconstruct the likely color patterns of fossil specimens.

Scientists at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, and the United Kingdom’s Diamond Light Source teamed up with researchers from the University of Manchester on the experiments, described in a new paper in Scientific Reports.


The critical factor here is melanin, which determines variation in skin tone in humans and plays a big role in the coloring of mammals and birds. But little is known about its exact chemistry, according to lead author Nick Edwards of the University of Manchester, because the stuff is notoriously difficult to characterize via the usual methods.

That’s where the advanced X-ray imaging capabilities come in. “These techniques are non-destructive, so they don’t destroy the samples you are studying,” SLAC scientist and co-author Dimosthenis Sokaras told Gizmodo. “And with the rapid scan imaging we have developed at SLAC, we can analyze objects ranging from a few centimeters to tens of centimeters in size in a few hours.”

Image: N. Edwards et al./Scientific Reports

This latest work builds on earlier research from 2011, when SLAC scientists used x-ray imaging to examine the fossilized remains of two birds (Confuciusornis sanctus) that lived 120 million years ago. They found traces of the pigment eumelanin, responsible for the brown eyes and dark hair found in many modern species, including humans. It would have been one factor (among many) that determined the patterns of colors for those birds.


But eumelanin isn’t the only pigment of interest to the scientists. Pheomelanin also plays a role, notably in the production of reddish/yellow hues. At the time, the team just didn’t have sufficient data to conduct a similar examination focusing on pheomelanin.

Past studies have shown that pigmented tissues are richer in certain long-lived trace elements like zinc, calcium, and copper. So it made sense to target those elements in the new experiments. It also made sense to test this hypothesis in modern birds rather than ancient fossils, since the colors and pigmentation patterns are already known.


The team collected features from four species of birds of prey, shed naturally in sanctuaries: the Harris hawk, the red-tailed hawk, the kestrel, and the barn owl. Then they used X-ray fluorescent imaging to pinpoint concentrations of those key elements in the feathers.

This in turn enabled researchers to distinguish between the two types of melanin in samples, because there were subtle differences in he concentrations between the two. For instance, the presence of zinc bonded to sulphur compounds indicates the feather has pheomelanin, so it should have a reddish/yellow hue.


Now the Manchester researchers plan to apply what they’ve learned about those trace metal concentrations to fossilized specimens like those ancient birds, or dinosaurs. Was T. Rex predominantly black or dark brown, or did its coloration fall more in the reddish/yellow range?

“A fundamental rule in geology is that the present is the key to the past,” geochemist and senior author Roy Wogelius said in a statement. “This work on modern animals provides another chemical ‘key’ for helping us to accurately reconstruct the appearance of long extinct animals.”


[Scientific Reports]

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