Because
the annelids have soft bodies, fossilization is exceedingly
rare. The best-preserved and oldest specimens come
from
Cambrian Lagerstätten such as the Burgess
Shale of Canada, and the Middle Cambrian strata of the House
Range in Utah. Putative Annelid ichnofossils are
known from the Ediacara
Hills of Australia and the White
Sea Region of Russia. The Annelids are also well
represented among the Pennsylvanian-age Mazon
Creek fauna of Illinois.