Trace fossils may be impressions made on the substrate by an organism. Burrows, borings, footprints, feeding marks, and root cavities are examples. The term includes the remains of other organic material produced by an organism for example coprolites (fossilized droppings) or chemical markers. Stromatolites are sediment structures produced by bacteria. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization.