SOFT TISSUE PRESERVATION IN DINOSAURS AND BIRDS

Unlike bones, soft tissues are usually preserved as a special category of trace fossils that give some indication of size and shape, but not detailed structure or biochemistry. Many examples are preserved as "carbon films" that prove to be monotypic concentrations of fossilized bacteria. These concentrations reflect very localized conditions favoring the growth of specific species. They do not preserve the original biological structure, but resemble shadows cast by soft tissue at the time of decay. The anatomical distribution of these films may provide insight into the biology of bacterial colonies, and the anatomical significance of the structures they represent. A further source of soft tissue information is provided by natural casts in the sediment surrounding the bones. The combination of information from "carbon films" and soft tissue casts has recently provided a remarkable picture of soft tissue anatomy in some Mesozoic dinosaurs and birds.