About 130 million years ago, a small-feathered dinosaur danced across the open plains in what is now northeastern China, hiding in plain sight thanks to its striped tail and a "mask" of dark feathers.
Watch: Scientists analyse an ancient fossil and make a full-colour model of a dinosaur.
Scientists discovered this stealthy colour pattern after studying remarkably well-preserved fossils of Sinosauropteryx, a small carnivorous dinosaur that lived during the early Cretaceous. It may now be one of the few known examples of countershading in dinosaurs, a mix of dark and light body colouring modern animals still use as a method of camouflage.
Great white sharks, for example, are dark on top to blend in with murky waters when seen from above, but are lighter on their bellies so that they match the sky when viewed from below. Countershading also makes an animal appear narrower from the side, which can make it seem like a smaller, less attractive meal for predators.
In their study, published this week in Current Biology, study co-authors Jakob Vinther and Fiann Smithwick of the University of Bristol present their evidence that Sinosauropteryx was counter shaded. Based on preserved pigments found in the fossils, they say that the animal would have had a coat of rusty brown feathers on its back. From the side, the feathers would have starkly shifted from dark to light, with paler plumes running across its chest.
The dinosaur looked like "something between a roadrunner and a rock wallaby," Vinther says.
The result not only offers clues to how Sinosauropteryx looked, but also to how it might have hunted and evaded predators in an open, sunny landscape.
"We now can perhaps paint a better picture of which dinosaurs in this environment were interacting with each other," Vinther says. (This massive armoured dinosaur may have used camouflage to hide from predators.)
In recent years, scientists have been able to isolate and study melanosomes, which create the pigment melanin, preserved in fossilized feathers. These chemicals offer clues to what ancient animals looked like in life.
"When feathers are preserved, that's because there's melanin in there," Vinther says. "If there's no pigment there, the keratin just decays away and we have nothing left behind."
For Sinosauropteryx, the team examined three fossil specimens preserved in China, took photographs, and then mapped out their colour patterns based on the images. The researchers also created 3-D models of the dinosaur and made different images in varying lighting conditions.
Because Sinosauropteryx's colour contrast is more defined and higher up on its body, it likely lived in an open habitat in direct sunlight, they argue.
"[The] dark-to-light pattern on the body needs to balance out the shadows," Smithwick says. He adds that the research gives a more "holistic approach" to looking at the Sinosauropteryx specimen by analyzing its colour patterns and behaviours.
But Mary Schweitzer, a molecular preservationist at North Carolina State University, isn't sold on the data, and she says that the dinosaur's exact colouration is still speculative.
Fossils are preserved in different ways, which can make defining characteristics in multimillion-year-old specimens tricky. Sinosauropteryx was a feathered species, and Schweitzer says the bandit-like mask could have been the result of feathers falling around its face during degradation.
The three fossils are also different sizes, likely indicating different ages at their time of death, and Schweitzer says it's possible the tail banding is a juvenile trait that was lost in adults.
The fossils also do not have feathers in the abdominal region, which could mean, as the authors say, that the feathers were light in life and were not preserved due to lack of melanin. Or it could mean that they didn't exist at all. If the animal had gases in its stomach when it died, that part of its body may have exploded and left behind an uncoloured area in the fossil impression.
Vinther and colleagues were not permitted to take samples from the specimens, so they couldn't verify their results with chemical testing.
"We don't know anything about the anatomy of these guys," Schweitzer says, referring to the noninvasive nature of the study. "I don't believe that the data are strong enough to make any conclusive claims one way or the other."
By contrast, Vinther is much more confident in his team's conclusions: "Those colour patterns that we see stand for themselves."