Trace fossils can be classified according to Linnaean taxonomy, ethology
(inferred life history and behaviour of trace producing organisms), or
Trace fossils are usually identified using the combination of all the classification
principles presented above.
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
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)