Classification Principles

• Linnaean classification involves the using of a binomial system similar to that employed for body fossils and living species. Ichnotaxa include ichnogenera and ichnospecies, simply used to define morphological differences. In many cases is difficult to prove a direct relationship between trace producer and trace (e.g.. the trace produced by the genus Lithophaga is called, according to its shape, Gastrochaenolites), therefore is desirable an independent name for a particular trace morphology.


• Ethological (Behavioural) classification is a mechanism of distinguishing groups of traces on the basis of the behaviour of a group of organisms. The main types include:
• resting traces - cubichnia - created by active organisms while at rest or hiding from prey;
• locomotion traces - repichnia - tracks and trails created while moving across the sediment surface;
• dwelling traces - domichnia - three dimensional dwelling structures created by burrowing;
• grazing traces - pascichnia - horizontal feeding traces on the surface of the substrate;
• feeding traces - fodinichnia - three dimensional networks characterized by the combined functions of deposit feeding and dwelling.
• traps and gardening traces - agrichnia - regular, patterned branching structures used as traps for migrating meiofauna or as gardening systems where microbes might be cultured for food.
• predation traces - praedichnia - are common on hard substrates, as round drill holes in shells and shell damage by predators.
• equilibrium traces - equilibrichnia - are characterized by burrows that must be constantly adjusted within the substrate due the agradation and degradation processes.
• escape traces - fugichnia - occur as the animal flees to the new sea floor
• edifices built above the substrate - aedificichnia - are structures built of sediment, more or less cemented by the architect
• structures made for breeding purposes - calichnia - are structures built for raising larvae and juveniles.
 

Major categories of trace fossils according to behavioural classification and some illustrated ichnogenera: Cruziana; 2. Anomoepus; 3. Cosmorhaphe; 4. Paleodictyon; 5. Phycosiphon; 6. Zoophycos; 7. Thalassinoides; 8. Ophiomorpha; 9. Diplocraterion; 10. Gastrochaenolites; 11. Asteriacites; Rusophycus (after Benton & Harper, 1997)

• Preservational classification uses the relationship of the trace with the sedimentary surface. According to this criterion the traces can be exogenic (on the sediment surface) or endogenic (within the sediment itself). Traces can be found in full relief (with the boundaries of circular burrows clearly defined within the enclosing sediment) or semirelief, either on the upper surface (epirelief), or on the lower surface (hyporelief) of a sedimentary layer.

Terminology of trace fossil preservation depending on the relationship to sediment horizons (after Benton & Harper, 1997)