WHAT COLOR WERE THE DINOSAURS?

by Whit Gibbons

September 26, 2010

Anyone who has seen Barney knows that some dinosaurs are purple. And movies such as Jurassic Park and most children's' books about dinosaurs imply that these prehistoric leviathans were brightly colored. But how can we tell what color an animal was from a bone that has been buried for a hundred million years?

What color were the dinosaurs? Some paleontologists have assumed that the body color patterns of terrestrial animals now known only as fossils were comparable to those of modern-day vertebrates, but documenting color in particular species was considered impossible. During the past year, however, independent studies by scientists from China, England, and the United States have demonstrated that extinct relatives of the dinosaurs had body color and have even suggested what some of the body color patterns were.

Two points need to be considered when understanding how paleontologists know that dinosaurs had body coloration. First, the earliest birds were a direct evolutionary offshoot of the dinosaurs. Therefore, birds are more closely related to dinosaurs, as well as to alligators and crocodiles, than to today's modern reptiles such as snakes and lizards. Thus, some of the findings about the skin characteristics of dinosaurs have been based on examining feathers of ancient birds.

The second point is that some of the research has involved highly technical laboratory equipment at microscopic levels that revealed the presence of structures that are unimaginably small. The investigators examined the shape, size, and microstructural characteristics of fossilized melanosomes. Melanosomes are tiny bodies that are inside the cells of today's animals and that can produce color. Jakob Vinther of Yale University and colleagues examined fossilized feathers and found preserved melanosomes that had structural arrangements similar to those that produce color in modern birds. The discovery indicated that earlier birds and dinosaurs potentially used color displays.

Vinther and Quanguo Li of the Beijing Museum of Natural History and colleagues provided confirmation of variable plumage color in a feathered dinosaur from the Late Jurassic in China. Although it had feathers covering its body, it was not a flying animal. The specimen's face was dark gray with reddish brown speckling, a reddish brown crown, and white limb feathers with black markings on the tips. The investigators suggest that color may have been important during early feather evolution as a signaling mechanism in a manner similar to that of modern birds. Body colors can be important for attracting mates, in threat displays, and for certain forms of camouflage.

Meanwhile, Fucheng Zhang and Zhonghe Zhou of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, Michael J. Benton, University of Bristol, UK, and colleagues used scanning electron microscopy to study fossilized material from the Early Cretaceous of China. They examined skin structures, including the feathers of nonflying dinosaurs with pennaceous feathers. These are the feather type most people are familiar with, in which the feather has a main shaft with lateral vanes extending out from it. They also examined dinosaurs without true pennaceous feathers. The investigators determined that the melanosome structure was the same as that found in modern birds.

They discovered that a type of pigment called phaeomelanin, which is reddish brown to yellow, was present, as well as eumelanin, a pigment that is black gray. The phaeomelanosomes were the first ever discovered in fossil material. From a paleontological perspective, the research is significant in understanding the origins and relationships between birds and dinosaurs. Identifying the microscopic structures in the skin of nonflying dinosaurs as a likely evolutionary forerunner of true feathers is also important.

But for those of us who have been and continue to be fascinated with dinosaurs and who like looking at artists' renditions of what they looked like, it is comforting to know that some may have been colorful. To imagine a bright green Tyrannosaurus rex with red eyes and a yellow stripe down its back attacking a blue brontosaurus with red splotches is far more exciting than to imagine the same scenario if those two animals are both a dull gray.

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