Potential preservation of skin and intervertebral discs in a juvenile dinosaur (Edmontosaurus)
Soft tissue preservation in dinosaur fossils is relatively rare although a few examples have been found (Davis, 2014). We recovered a juvenile hadrosaur from the Hell Creek Formation of Montana with both skin impressions and potential preservation of intervertebral disks. Thin sections across original skin impressions have a dark, apparently organic rich, carbonaceous layer where skin would have been present in the original animal. This strongly suggests that the soft tissue was mineralized and preserved. However, we were unable to optically image cell boundaries similar to those figured by Manning, et al, (2009) that might demonstrate the presence of mineral cements that might outline the original cell boundaries. Apparently, the tissues in our hadrosaur were too decomposed to preserve such fine detail.
Thin sections of the disks that occur between vertebrae are composed of fine-grained sandstone, which filled in the spaces between the vertebrae. Although this is a process that is not completely understood, it is clear that the skeleton lacks the presence of mineralized cartilage. The dark colored spots in the disks may, however, represent bits of cartilage material that has largely decomposed into carbonaceous material.
Of the three types of preservation of dinosaurs suggested by Schweitzer (2012) our specimens has definite preserved impressions, possible compressions, but so far we have been unable to demonstrate preservation of three dimensional permineralized tissue.