Coprolites

Coprolites – fossil excrement from animals – are numerous in Mazon Creek concretions. Sizes range from tiny pellets to thick masses and are composed of calcium- and phosphate-rich material (hydroxyapatite). They often include bone fragments, scales, ostracodes, portions of bivalves, bony fish, crustaceans, and sometimes plant material. Most coprolites cannot be matched with the animal that produced them, although those with a spiral shape are considered to be from sharks.