Ichnofossils

Ichnofossils, or trace fossils, are geological records of biological activity rather than the preserved remains of the organisms themselves. Common examples include footprints and trackways, burrows and borings, feeding marks, nests, and coprolites (fossilized feces). Coprolites are often treated as trace fossils in ichnology.

They form when an organism interacts with a sediment or substrate in a way that leaves a mark, and that mark becomes preserved as the sediment lithifies. This can produce an impression on a bedding plane, a filled burrow, or a mineral cast.

Ichnology, the study of trace fossils, focuses on the morphology of traces rather than the identity of the maker. Because many organisms can produce similar traces, ichnotaxonomy classifies traces into ichnogenera and ichnospecies based on form and behavior rather than the specific species. Notable ichnotaxa include Skolithos (simple vertical burrows), Cruziana (trilobite feeding trails on bedding planes), and Arenicolites (worm burrows). Paleodictyon describes a polygonal, net-like trace, among others. Dinosaur tracks are assigned to ichnotaxa such as Eubrontes and Grallator depending on shape and size.

Trace fossils provide information about behavior, locomotion, feeding, and dwelling, and they record aspects of the paleoenvironment such as substrate type, energy, and water depth. They can be preserved in a range of sediment types, most commonly in sedimentary rocks like sandstones, siltstones, and carbonates.

Limitations include ambiguity in linking a trace to a particular organism, and alterations that obscure original details. Despite this, ichnofossils are a key source of behavioral and ecological information in paleontology.