Fossils have revealed virtually all we know about dinosaurs, but their color has been left to our imagination. Indeed, paleontologist Michael Benton of the University of Bristol in the United Kingdom always taught his students that the colors of dinosaurs were something we would never know.
In a paper published online in Nature today, Benton and colleges describe fossilized melanosomes. These organelles contain melanin, a group of pigment compounds in skin, fur, and feathers. The structure of the melanosome reveals the color it bestows, and those shapes, the new work shows, are preserved in fossils. "We are extraordinarily lucky that each of the main pigment forms of melanin is contained in a different shaped organelle," Benton said at a briefing yesterday.
The team looked at both fossil birds and dinosaurs. When studying the 125-million-year-old Cretaceous bird Confuciusornis, they detected two types of melanosomes: Eumelanosome, which gives rise to black-gray color, and pheomelanosome, which results in a reddish-brown color. This is the first time pheomelanosomes have been found in early birds.
The dinosaur Sinosauropteryx, from the same time, had featherlike bristles running across its head, back, and tail. These bristles also turned out to contain pheomelanosomes, revealing that the dinosaur had reddish-brown stripes covering the tail. The researchers suggest that areas completely missing melanosomes were most likely white. Benton said that several other pigments probably contributed to the hues of animals during the Cretaceous, as they do today.
Coloring in dinosaurs isn't child's play. Identifying these pigment structures over all the preserved bristles and feathers of a fossil would take "probably hundreds of hours of electron microscopy" said Stuart Kearns of the University of Bristol and one of the paper's authors.
According to Benton, his team's report also resolves the long-standing debate over whether dinosaurs had feathers. "We can now say for sure that these bristles are feathers," he says, because finding organic matter from skin is much less likely. The question remaining is whether these feathers developed for insulation, camouflage, or communication.
A longtime skeptic of dinosaur feathers, evolutionary biologist Alan Feduccia of the University of North Carolina, Chapel Hill, disagrees. He says Benton and co-authors "make a leap of faith going from Confuciusornis to Sinosauropteryx." He suggests these melanosome-like structures might stem from preserved bacteria, for example. If the structures are indeed melanosomes, they do not necessarily have to come from feathers but could in fact be remains of skin. In that case, he says, the technique could be used to study even earlier dinosaur fossils.
Another dino-feather skeptic is more impressed, although not completely persuaded. Paelontologist Theagarten Lingham-Soliar of the University of KwaZulu-Natal in South Africa calls the new work the "first study using hard science from the supporters of protofeathers in dinosaurs."