Ichnology

1. Ichnology Ichnology is a subfield of geology that deals with traces of organismal activity. The area of ichnology concerned with trace fossils is paleoichnology. Plio-pleistocene ancient hominid footprints preserved in volcanic ash at Laetoli in Tanzania, Africa.

2. So why is it useful? Paleontologists use ichnology to decode the possible anatomy and behavior of trace-making fossils even if no body fossils can be found. Protichnites, an ichnogenus of arthropod walking activity found in central Wisconsin in Late Cambrian sandstone.

3. What kind of fossil traces do organisms leave? There are several types of organismal traces that can be fossilized. Examples include: • Burrows Climatichnites fossilized burrow from Central Wisconsin, Late Cambrian.

4. Other examples include: Coprolites, or fossilized dung. Coprolites are valuable because they give information on the diet and behavior of instinct animals, rather than just morphological information. Coprolite of carnivorous dinosaur, found in southwestern Saskatchewan, Canada.

5. Another interesting ichnofossil are gastroliths, or “stomach stones” or “gizzard stones” used by animals for grinding food. Modern animals such as herbivorous birds, crocodiles, alligators, seals, and sea lions use gastroliths. Some paleontologists also believe sauropod dinosaurs may have used them for chewing and that plesiosaurs may have used them for ballast.

6. Other ichnofossils include: • Borings and etchings • Regurgitaliths • Nests • Leaf mines • Bite & gnaw structures • Organismal secretions, such as coccoons, pupal casings, spiderwebs, embedment structures, and plant galls.

7. Classification Because trace fossils cannot always be positively identified to the species that produced them, they are given scientific nomenclature separate from morphologically classified species. The International Code of Zoological Nomenclature defines an ichnospecies as a “taxon based on the fossilized work of an organism.” They are given an italicized Latin genus and species name with the prefix “ichno-” added for clarity.

8. Ichnofossils can also be classified by the type of behavior the organism engaged in while producing the fossilized traces. The Seilacherian System is a long-accepted system of classifying an ichnofossil based ethological divisions, including: • Cubichnia– traces of an organism left in soft sediment (ex: outline of a starfish in sand). • Domichnia – dwelling structures that represent the life position of the organism (ex: burrows). • Fodinichnia – feeding traces which are formed as a result of organisms disturbing the sediment in their search for food. • Pascichnia– a different type of feeding trace caused by grazers scraping substrate in search of food. • Repichnia – locomotory tracks that show evidence of organisms moving from one station to another

9. Sponge borings and encrusters on a modern bivalve shell from North Carolina, a modern example of Domichnia.

10. Footprint of ichnogenus Grallator, a bipedal theropod dinosaur that roamed Pangaea in the Late Triassic and early Jurassic. Below are examples of Repichnia. The ichnospecies Anomoepusgracillimus, a set of footprints found in the Late Triassic beds of the Connecticut River Valley, Massachussets