Colorful feathers and pelts exploded on the scene soon after early birds and mammals evolved feathers and fur more than 150 million years ago, suggest researchers in a study of both fossils and living creatures.
Scientists have known since the 1990s that some dinosaurs bore feathers, and more recent research has provided clues to the feathers' true colors. The new study broadens the palette of colors of this ancient world, and perhaps points to surprising metabolic changes occurring in early birds and mammals. (Read "Evolution of Feathers" in National Geographic magazine.)
In the Nature journal study led by Quanguo Li of the China University of Geosciences in Beijing, an international team sampled ancient and modern "melanosomes," pigment-containing structures found inside skin, feather, and hair cells that impart different colors, depending on their shape. The team found a sudden rise in the diversity of melanosomes around 150 million years ago, around the same time that the dinosaur lineage leading to birds developed birdlike feathers with barbs branching off from a central shaft. The melanosomes in the study contained the brown, black, and gray pigments that make feathers iridescent.
"Definitely the results were surprising," says study co-author Julia Clarke of the University of Texas at Austin. "We were surprised to see a similar spread of colors in early mammals as in feathered dinosaurs." (See "Pictures: Dinosaur's Flashy Feathers Revealed.")
In the study, the researchers looked on a microscopic level for melanosomes from 181 living creatures and 13 fossilized lizards, turtles, dinosaurs, and pterosaurs, the iconic flying reptiles of the dinosaur era. The skin, fur, and feather samples of modern-day creatures came from museums, and the fossil samples were studied with scanning electron microscopes at Li's university.
The early mammals and first feathered dinosaurs, ones belonging to a group called maniraptors that gave rise to birds, seem to have possessed the same skinny-shaped melanosomes seen in their modern-day descendents. Reptiles and other dinosaurs didn't.
That points to a rapid proliferation of different dark hues among both early feathered dinosaurs and early mammals. The maniraptor feathered dinosaurs were the first ones with long "pinnate" feathers, and the early mammals were the first ones with hair.
"This study is certainly interesting as it suggests that there was a major increase in melanosome," said paleobiologist Maria McNamara of Ireland's University College Cork, who was not on the study team. As a result of the increase, color production leaps into prominence as a major driver in the evolution of bird feathers, she suggests.
But why these pigments spread so rapidly remains an open question, with the study authors favoring a theory that points to another role for melanin, the pigment protein contained in melanosomes.
"The story wasn't as much about color, we think, as it was about physiology," Clarke says.
Melanin, the pigment protein inside melanosomes, is also involved in metabolism—how animals burn energy in their cells, Clarke says. These pigments broadened at a time when the first warm-blooded mammals and the flightless, feathered dinosaurs ancestral to modern birds were evolving.
"So this study offers a tantalising prospect—suggesting evidence for links between evolution of coloured feathers and metabolism," McNamara said, by email.
Other outside experts, such as evolutionary ornithologist Richard Prum of Yale, are more skeptical of linking the rise in melanosome diversity to metabolism. "I think the data is very good in the study, but the interpretation is more of a question," Prum says.
"It seems simpler and more likely to me that once long feathers and fur evolved, that color alone served as way for evolution to occur quite rapidly, resulting in more color diversity," he says.
Quest for Color
Overall, the results paint a picture of a vibrant ancient world, with a diversity of feathers worn by the first, flightless birds and varied pelts worn by early mammals.
"These are the pigments that would make feathers look iridescent, or glossy," Clarke says. The pigments wouldn't have made mammal fur glossy, she says, but would have affected darker shadings of their hair.
Knowing exactly what ancient creatures looked like will remain difficult, Clarke adds, because pigments for brighter colors, such as yellow, don't seem to be preserved in the same way as the dark ones investigated in the study.
Follow Dan Vergano on Twitter.