Feathered Dinosaur Fossils Reveal Color Pigments

Recent investigations by a team of Yale University paleobiologists have revealed color pigmentation in the plumage of the oldest known feathered dinosaur, Anchiornis huxleyi, according to a report published in Science Magazine. (See also our previous article on Anchiornis huxleyi.) The discovery of coloration in dinosaurs is significant in its own right, but paleontologists say it may also shed new light on why feathers evolved in certain dinosaurs in the first place.

The work of Yale University paleobiologist Jakob Vinther and his colleagues follows up on the groundbreaking research of Michael Benton, a paleontologist at the University of Bristol in England. Both investigations have revealed microscopic pigmentation structures known as melanosomes in the fossilized feathers of A. huxleyi and, in the case of Benton's investigations, other dinosaur species.

Vinther and his team examined microscopic melanosome structures at 29 separate sites on a specimen of A. huxleyi unearthed last year in northeastern China. They looked at two types of feathers: small, simple feathers covering the creature’s body and skull, and the longer, more complex feathers on its forelimbs (proto-wings), legs and feet. Almost all of the feathers examined showed well-preserved remains of the pigment-bearing melanosomes.

The Yale University team compared the size, shape, arrangement and density  of melanosomes in each fossil feather with colored feathers of modern birds. This allowed them to develop a picture of the coloration of A. huxleyi's plumage. “Using those comparisons, we can reliably predict (the creature’s) color and map the whole animal,” said Vinther.

The color schematic reveals that A. huxleyi had grey and black feathers on its body; the long feathers on the front and side of its crest were grey, and the feathers on the top and back of its head were reddish-brown. A. huxleyi's head and neck featured reddish-brown spots, and its legs and winglike forelimbs had prominent white stripes.

The University of Bristol's Michael Benton says the Yale team's findings “reveal an enormous array of information.” He notes that the black-and-white bars on A. huxleyi’s proto-wings, as well as its colorful crest, are similar to coloration features in modern birds. More significantly, understanding when color developed in feathers or filament structures may aid in solving the question of why these structures evolved to begin with, says Benton. For example, he notes that A. huxleyi’s feathered proto-wings weren’t large enough to actually carry the creature’s weight in flight. “What’s the function of half a wing?” he asks.

Paleontologists have suggested that because feathers appear in the fossil record long before flight-capable birds, feathers may have initially had a behavioral function, possibly for sending visual signals, and only later were used for flight. Vinther and his colleagues speculate along similar lines, suggesting that in addition to communicating with members of its own species -- for instance, in ritual mating behaviors and for driving off rival suitors -- their boldy colored plumage could have been used for startling an attacking predator or to flush their prey out of hiding.

This visual communication component seems to be borne out by looking at the morphology of dinosaurs, specifically the prevalence of very large eyes and sizable optic lobes in their brains. Says Philip J. Currie, a paleontologist at the University of Alberta in Edmonton, Canada, “Ancient creatures didn’t just sprout feathers and start flying. The feathers were there for another reason first... Dinosaurs were very visual animals, just like birds are.”