Annelids probably originated in the Precambrian. Indeed, a few Vendian fossils, such as Spriggina, were once assigned to the Annelida; however, this identification is now doubted. Definite annelids appeared in the Cambrian. Pictured above is Canadia, from the Middle Cambrian Burgess Shale of British Columbia.
Canadia and other Cambrian polychaetes had no jaws, but some later polychaetes developed hard jaws, which are sometimes mineralized with iron oxide. Such polychaete jaws are fairly common in the fossil record, and are known as scolecodonts.
Body fossils of polychaetes are rarer, being generally restricted to Lagerstatten - localities with unusually good preservation of fossils. Mazon Creek, near downtown Chicago, is one of these localities where polychaetes have been found. Fossil oligochaetes are much rarer, and there are almost no fossil hirudineans (leeches) known.