One of the most tantalizing mysteries about dinosaurs—and long-extinct fauna in general—is their coloring. Was Tyrannosaurus rex flamboyantly decked out in bright colors, or something more modest? What hues did the first flying dinosaurs sport on their feathers? To reconstruct not only the morphologies of these magnificent animals, but also their coloration patterns, has been a goal of paleontology for centuries.
Paleontologist Ryan Carney of Brown University has been a frontrunner in this field, particularly with regards to the transitional species Archaeopteryx. Carney affectionately refers to the animal the "Mona Lisa of paleontology" because of its rich cultural history and its hallowed status as a watershed species in bird evolution.
In 2011, Carney and his colleagues published an in-depth analysis of the "melanosomes" on a fossilized Archaeopteryx feather. Melanosomes are organelles that produce and transport melanin, the most abundant pigment in the animal kingdom, and they are the key to decoding the colors of long-dead species.
"The size and shape of the melanosomes is very tightly linked to the type of color it produces," Carney told me over the phone. "Rounder meatball-shaped melanosomes provide the reds and sometimes yellows. Elongated hot-dog-shaped ones produce the greys and the blacks and iridescence."
"Based on the feathers in the fossils, and comparing them to living bird melanosomes, we can tell what colors [dinosaurs] were with a quantitative degree of certainty," he added. In the case of Archaeopteryx, the feathers were determined to be matte black.
Carney's study sparked a controversy, with some paleontologists arguing that the melanosomes were actually microorganisms, while others disputed his color findings, suggesting thatArchaeopteryx was black and white. Today, Carney will be presenting new evidence refuting these contradictory findings at the 74th Meeting of the Society of Vertebrate Paleontology.
The evidence was collected using a technique known as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). "It's a really neat new method and something that we have turned to because there has been some controversy that melanosomes are a similar size and shape as bacteria," he said.
The idea is to bombard fossils with atoms that dislodge and scatter particles, molecules, and ions from the fossilized surface. "What the machine does is calculate how long the time of flight is," Carney explained. "Basically, the heavier particles don't fly as far as the lighter particles, so you can infer the mass of those particles based on the time of flight. By looking at all of that information you can then reconstruct the molecular structure of what was on that surface."
Analyzing Archaeopteryx feathers using ToF-SIMS confirmed Carney's original findings. "We have very clear evidence that [the feather] was completely black and not black and white," he told me, and that the structure are definitely pigment-bearing melanosomes, not microbes.
Carney will be presenting these new findings just a week after another intriguing article on dinosaur color, entitled "Beyond the rainbow," was published in Science. The article's first author, paleontologist Marie-Claire Koschowitz of the University of Bonn, argued that dinosaurs may have evolved feathers in order to project brilliantly colorful displays, with flight being an adaptive afterthought.
"Up until now, the evolution of feathers was mainly considered to be an adaptation related to flight or to warm-bloodedness, seasoned with a few speculations about display capabilities" Koschowitz said in a statement.
"I was never really convinced by any of these theories," she continued. "There has to be some particularly important feature attached to feathers that makes them so unique and caused them to spread so rapidly amongst the ancestors of the birds we know today."
Koschowitz thinks that feature was the astute color vision of dinosaurs, which may have been a lot more sophisticated than ours. Feathers allow for a diversity of colors and iridescence that skin and fur do not. Perhaps dinosaurs evolved feathery plumage because they were able to appreciate a much larger range of colors than other clades could—including mammals.
Along those lines, Carney is eager to isolate the signature of several colors in dinosaur fossils, beyond the black-winged Archaeopteryx.
"Now what we're trying to do with this ToF-SIMS method is to look for other types of pigments, other organic compounds, and really try to expand the palate of colors for reconstructing ancient life," he said. Indeed, he has already isolated a melanosome that produces iridescence in a Microraptor fossil, suggesting the small raptor had a glossy sheen to its plumage.
Identifying other hues and patterns will take time, and is likely to be as controversial an endeavor as Carney's 2011 findings. But if we end up with a paint-by-numbers guide to dinosaur coloration, it will have been time well-spent and controversy well-earned. The next generation of dinosaur-obsessed kids deserves to know exactly what T-Rex looked like, rainbow feathers and all.