Scolecodonts -- Fossil Polychaete Worm Jaws

Many post-Cambrian polychaetes possessed hard jaws, which are sometimes mineralized with iron oxide. Such polychaete jaws are fairly common in the fossil record, and are known as scolecodonts. This illustration of two scolecodonts is taken from the classic 19th-century paleontology textbook of Karl Zittel.