After the discovery of the slab containing the holotype material of Sinosauropteryx was initially discovered one of the more important characteristics of the animal's anatomy was immediately visible. The impressions of the filaments appeared as a reddish brown band of small fibers extending from the crown of the skull to the tail. Some of these fibers are seen on the ventral edge of the tail as well. These are also visible on the counter slab and on both slabs the disorganized appearing fibers are slightly removed from the spinal column. This gap has been hypothesized to represent the area where muscle and skin would have existed during life. The missing soft tissue would have, therefore, held the proto-feathers before death. These proto-feathers, as they appear in the fossil, look like a mohawk stretching the length of the small dinosaur's body. Due to their disorganized structure, individual filaments have not been studied. The body was covered in two described filaments; however, the hypothetical types of filament (referred to as thick and thin) have not been entirely validated. However, the thicker filaments are thought to be stiffer than the thin filaments. Thicker filaments also lie at angles to these thinner filaments whereas the thin filaments are parallel to one another. All of these filaments would have made for a short down-like layer of proto-feathers that would have certainly kept Sinosauropteryx warm.