At one point or another, almost every general book about dinosaurs I have ever seen has said the same thing: we cannot know what color dinosaurs were. Scientists have found the skin impressions of some specimens, but as far as we know these traces contain nothing that might tell us what color those dinosaurs were. As described in this week's issue of the journal Nature, however, scientists have been developing a technique that may allow us to see the colors displayed by some dinosaurs, and it is thanks to their connection with birds.
Last year the journal Biology Letters published the results of a study that identified preserved microstructures related to color in the feather of a fossil bird. The scientists could not say for sure what colors the feather exhibited in life, but they were able to document minute differences in the feather that are seen in living birds, meaning that evidence of color was preserved in the fossil even if it could not be fully understood yet. Now a different team of scientists has published a new study that has accomplished a similar task, but this time for two feathered dinosaurs and one of their bird relatives.
What the scientists behind the Nature study were looking for were melanosomes. These are color-carrying structures found inside pigment cells and are partially responsible for the colors we see in many organisms. The paleontologists found them in abundance in the feathers of the dinosaurs Sinosauropteryx and Sinonithosaurus, as well is in the preserved plumage of Confuciusornis. The structures were not preserved bacteria or some other remnant. Instead they were the preserved vestiges of dinosaur cell structure.
Clearly these animals had color-carrying cells in their feathers, but what color were they? That is a more difficult question to answer. The fossils that were examined contained two types of melanosomes: eumelanosomes and phaeomelanosomes. From the study of living organisms we know that eumelanosomes are associated with dark colors (i.e. black) while phaeomelanosomes are associated with lighter colors (i.e. yellowish to red). They cannot tell us specifically what color the dinosaurs were, but they can help us confirm color patterns and be used create hypotheses. The tail of Sinosauropteryx, for example, contains bands of feathers stuffed with phaeomelanosomes, and so the authors of the new paper suggest that it might have had bands of rich, reddish tail feathers. This hypothesis will require more evidence to confirm, however, especially since scientists are still learning how melanosomes are involved in producing particular colors.
The new research is a step closer to understanding what colors some dinosaurs were, and it is another piece of evidence confirming that the structures preserved around dinosaurs like Sinosauropteryx and Sinornithosaurus really are feathers. The melanosomes are contained entirely inside the feathers, just like in living birds, and there no longer can be any reasonable doubt that these animals were feathered dinosaurs. Even better, this line of inquiry has only just begun, and perhaps in a few years we will be able to tell with greater certainty whether dinosaurs were as colorful as their living relatives.
Zhang, F., Kearns, S., Orr, P., Benton, M., Zhou, Z., Johnson, D., Xu, X., & Wang, X. (2010). Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds Nature DOI: 10.1038/nature08740