Attaching the muscles, tendons, and other soft tissues to a reassembled dinosaur skeleton first requires the identification of muscle attachment sites on the bones. This information in combination with comparative and functional morphology data can then be used to generate soft tissue reconstructions of the fossil dinosaur. Muscles often leave residual attachment scars on hip, shoulder, and head skeletal regions. These characteristic scars (most apparent in well preserved bone) provide information on muscle placement, mass, and function. For example, in Iguanodon dinosaur skeletons, muscle scars on its ornithichian hip joint revealed its muscle pattern as intermediate between birds and crocodiles. After the muscle mass is recreated around a skeletal (fiber glass) model, other soft tissues such as skin may be added to the reconstruction. Though rare dinosaur skin impressions have been found that indicate rough, high-relief textures, the hues and coloration patterns of dinosaur skin remain remain a mystery.