A small, feathered dinosaur known as Sinosauropteryx had a stripe across its face to help it hide from both predators and prey. Around 130 million years later, the stripe reminds zoologists of a bandit mask. Of course, Sinosauropteryx was trying to hide its presence, not just its identity, so it used several other forms of camouflage as well, including a delightfully stripy tail.
“Vision was likely very important in dinosaurs, just like today’s birds, and so it is not surprising that they evolved elaborate color patterns,” said University of Bristol PhD student Fiann Smithwick in a statement.
Until recently, our ideas of coloring for extinct creatures, particularly those that have been dead as long as dinosaurs, were almost entirely guesswork. However, in the last few years, melanin has been detected in some fossils, indicating the presence of darker colors. It's absence can be taken to imply lighter parts of the body.
Smithwick and co-authors of a paper in Current Biology examined three of the best-preserved specimens of Sinosauroperyx, finding patches of dark coloring from what were once feathers. The consistency of patterning between the different specimens gave the authors confidence that their observations were accurate, rather than missing areas where melanin degraded in a consistently dark animal.
Melanin acts as a preservative, so the dark-colored patches have survived while lighter counterparts have not. The paper acknowledges the possibility unpreserved areas were actually lacking feathers entirely, but if so, it seems the underlying skin or scales were similarly lightly colored. However, the authors suspect the feathers provided insulation, probably besides other benefits, which would make partial covering unlikely.
Many living birds, and some other animals, have a facial stripe. For those, like birds, that have dark eyes, these stripes decrease the chance that either predators or prey will locate their most vulnerable organs. Darker colors around the eyes also help reduce glare from reflections for animals living in sunny conditions, and even more so around rivers where light reflects off water. Dark facial stripes are also sometimes used to warn off predators, but the authors consider this unlikely in Sinosauroperyx's case.
The patterns Smithwick found on Sinosauroperyx's body, particularly the sharp transition from dark to light areas, match those of modern animals living in open habitats such as grasslands. The Jehol deposit in Liaoning, China, where Sinosauropteryx was found, has been thought to have been forested, but the authors interpret their work as indicating a more mixed environment.
The tail banding could serve many purposes, including as camouflage and to confuse and distract predators. It could also have been used for sexual display. As the longest tail relative to body size of any known theropod, whatever it did was probably important.