English: Rusophycus pudicum Hall, 1852 - trilobite trace fossils from the Ordovician of Ohio, USA. (CMC IP 61254, Cincinnati Museum of Natural History & Science invertebrate paleontology collection, Cincinnati Museum Center, Cincinnati, Ohio, USA)

Trace fossils are any indirect evidence of ancient life. They refer to features in rocks that do not represent parts of the body of a once-living organism. Traces include footprints, tracks, trails, burrows, borings, and bitemarks. Body fossils provide information about the morphology of ancient organisms, while trace fossils provide information about the behavior of ancient life forms. Interpreting trace fossils and determination of the identity of a trace maker can be straightforward (for example, a dinosaur footprint represents walking behavior) or not. Sediments that have trace fossils are said to be bioturbated. Burrowed textures in sedimentary rocks are referred to as bioturbation. Trace fossils have scientific names assigned to them, in the same style & manner as living organisms or body fossils.

Trace fossils are also called ichnofossils. The study of traces and trace fossils is ichnology.

The trace fossils shown above are convex hyporeliefs - they are on the bottom surface of a limestone bed. These burrowing traces were made by one or more trilobites, likely engaged in the search for food. The trace maker was a Flexicalymene trilobite.

Trilobites are extinct marine arthropods. They first appear in Lower Cambrian rocks and the entire group went extinct at the end of the Permian. Trilobites had a calcitic exoskeleton and nonmineralizing parts underneath (legs, gills, gut, etc.). The calcite skeleton is most commonly preserved in the fossil record, although soft-part preservation is known in some trilobites (Ex: Burgess Shale and Hunsruck Slate). Trilobites had a head (cephalon), a body of many segments (thorax), and a tail (pygidium). Molts and carcasses usually fell apart quickly - most trilobite fossils are isolated parts of the head (cranidium and free cheeks), individual thoracic segments, or isolated pygidia. The name "trilobite" was introduced in 1771 by Johann Ernst Immanuel Walch and refers to the tripartite division of the trilobite body - it has a central axial lobe that runs longitudinally from the head to the tail, plus two side lobes (pleural lobes).

Classification of trace maker: Animalia, Arthropoda, Trilobita, Polymerida, Calymenidae

Stratigraphy: Fairveiw Formation, lower Maysvillian Stage, middle Cincinnatian Series, Upper Ordovician

Locality: unrecorded/undisclosed site along Colerain Avenue (probably a roadcut or a construction site), Cincinnati, Hamilton County, southwestern Ohio, USA