What color is your dinosaur?

There are a few steps between discovering an animal’s fossil and sussing out what it actually looked like. Step one, as this Smithsonian guide explains, is to put the bones together, drawing on knowledge of other skeletons of the same species to fill in whatever’s missing. Step two is to determine the shape of the muscles using markings on the bones. Step three is to puzzle together the exterior: Did the fossil contain horns or other armor? Does the shape of a bone indicate that feathers were attached to it?

The step after that is where scientists can get stuck. Bone lasts through hundreds of millions of years, but skin does not. Skin impressions—the patterns left in the dirt around the body—can tell researchers if an animal was scaly or smooth, but these impressions are rare.

Read more from The Atlantic here.