Scolecodont

thumb|right|An Ordovician scolecodont from Estonia

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