Indiana Worms

A scolecodont is the jaw of a polychaete annelid, a type of fossil-producing segmented worm useful in invertebrate paleontology. Scolecodonts are a diverse group of  microfossils, which range from the Cambrian period (around half a billion years ago at the start of the Paleozoic era) to the present. However, scolecodonts are reported most commonly from Ordovician, Silurian and Devonian marine deposits of the Paleozoic era.  

Since the other classes of annelids (specifically, the earthworms and leeches) lack hard parts, only the sea-dwelling polychaetes are frequently represented in the fossil record. Polychaetes are commonly fossilized due to their chitinous teeth and their dwelling tubes made of durable calcite (a calcium carbonate), hardened mucus (a.k.a. parchment), and/or chitin-like cement.