Champsosaur skin impression
Notice the scales on the skin (around the
"knee") and webbing between the toes. The flesh
appears like a ghostly halo, while the vertebrae and other bones are sharp and three-dimensional. This reflects the different ways in which hard
parts (bone and teeth) and soft tissue (such as skin and internal organs) are
fossilized. Bones become fossils as minerals replace organic structures on a
molecular level. In contrast, bacteria create the blurry traces of soft tissue.
As the bacteria consume skin, fur, feathers, and other soft tissue, they leave
metabolic deposits in the shapes of their meals.