Trace fossils are the term for biogeological activity that can be observed outside of skeletal or body fossil remains. Trace fossils, also known as ichnofossils, are any observable fossil phenomena that do not represent the preserved organism itself, but rather evidence of its behavior, movement, or interaction with its environment. These fossils help paleontologists understand how organisms lived, how they moved, fed, rested, or even reproduced, offering a dynamic window into the past that body fossils alone cannot provide.
Examples of trace fossils include:
- Feces, known as coprolites, which can reveal diet and digestive processes.
- Footprints, trackways, and crawl marks, which inform scientists about gait, speed, and group behavior.
- Liquid waste impressions, such as urolites, rare but occasionally preserved under the right conditions.
- Burrows, which reflect dwelling or feeding activity (e.g., Skolithos, Thalassinoides).
- Root cavities and root traces, important for understanding past plant ecosystems.
- Gastroliths (stomach stones), which are sometimes included as behavioral indicators.
- Resting traces, called cubichnia, which capture the imprint of an organism lying still.
- Feeding marks, such as fodinichnia (burrowing feeding patterns) and pascichnia (grazing trails).
- Escape structures, or fugichnia, created when an animal tries to flee sediment burial events.
- Bioerosion marks, such as borings or scrapings in hard substrates (like shells or rocks), showing interaction with other materials or organisms.
Ichnotaxa[]
Animals or organisms described solely from trace fossils are placed into a separate taxonomic category called ichnotaxa, and their classification is often treated with caution similarly to nomina dubia. Since the same type of trace could be made by multiple unrelated species—or a single species could leave behind many types of traces depending on its activity or life stage—ichnotaxa are often considered form taxa, based more on morphology than on biological identity. As a result, some paleontologists are skeptical of assigning full taxonomic status based only on trace evidence.