Fig. 1.

Arthropod fossil from the Burgess Shale described by C. D. Walcott in 1912 as Sidneyia inexpectans (named in honor of his son, Sidney). The beautiful traces of soft tissue preserved as carbonaneous films include the feathery gill structures seen readily in the photograph. The Burgess Shale, the most famous of the Cambrian fossil deposits, is marked by exceptional preservation of soft tissue, including remarkable records of soft-bodied organisms lacking skeletal remains. (Image is in the public domain; from ref. 9.)