Coprolite of an Ichtyosaur
A coprolite is fossilized faeces. Coprolites are trace fossils, not body fossils. They give evidence of the animal's behaviour (in this case, its diet).
The name is taken from the Greek words κόπρος (kopros, meaning "dung") and λίθος (lithos, meaning "stone"). They were first described by William Buckland in 1829.