Ichnofossils

Introduction to Ichnofossils and classification

1. Trace Fossils
•Trace fossils are the records of biological activity left in rock, that is,
evidence that organisms were active there. They do not include hard
parts, a.k.a. “body fossils”
•Long temporal ranges -they are not useful as indicators of age
•Largely facies dependant-they are very useful as indicators of
depositional environment
•Biogenic sedimentary structures, where preserved intact, are closely
related to the environment in which they formed -they are not
transported as some body fossils can be
•Common in rocks that otherwise are unfossiliferous. The causative
organisms are typically not preserved.

2. •Different organisms may produce a single structure, and the same
individual or species can produce different structures corresponding
to different behaviour–it can be very difficult to know what made the
trace
•The same individual may produce different structures corresponding
with identical behaviourbut in different substrates –interpreting
environments from trace fossils can be difficult
•Identical structures may be produced by the activity of systematically
different trace-making organisms where behaviouris similar (and
similar ichnofossilscanbe formed by organisms from different periods
that have similar behaviours)

3. Characteristics of Trace Fossils that make them
valuable in Paleoecology
•Long Time Range –allows rocks of widely different ages to be
compared.
•Narrow Facies Range –most trace fossils are found in their preferred
environment.
•No Secondary Displacement –can not be transported like body fossils.

4. Classification Principles
Trace fossils can be classified according to Linnaean taxonomy, ethology
(inferred life history and behaviourof trace producing organisms), or
preservationaltype.

5. Linnaean classification
•It involves the using of a binomial system similar to that employed for
body fossils and living species.
•Ichnotaxaincludeichnogeneraandichnospecies, 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
genusLithophagais called, according to its shape,Gastrochaenolites),
therefore is desirable an independent name for a particulartrace
morphology.

6. Ethological (Behavioural) classification
•It is a mechanism of distinguishing groups of traces on the basis of the
behaviourof a group of organisms.
•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.

7. •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

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

10. Preservationalclassification
•It uses the relationship of the trace with the sedimentary
surface.
•According to this criterion the traces can beexogenic(on the
sediment surface) orendogenic(within the sediment itself).
•Traces can be found infull relief(with the boundaries of
circular burrows clearly defined within the enclosing
sediment) orsemirelief, either on the upper surface
(epirelief), or on the lower surface (hyporelief) of a
sedimentary layer.

12. Burrows
Circular and
Elliptical
Structures
•Laevicyclus
Simple
Structure
•Vertical Form
•Skolithos
•Plug Shaped
•Bergaueria
•Conichnus
•Horizontal
•Palaeophycus
•Planolites
Branched
•Dichotomously
Branched
•Chondrites
•Y-T Shaped
•Ophiomorpha
•Thalassinoides
•Bundled
•Phycodes
Winding and
Meandering
•Pliated
•Gyrochorte
Spreiten
•U Shaped
•Rhizocorallium
•Zoophycos
Coiled
Structures
•Coiled
•Gyrolithes

13. Others
Trails
•Oniscodichnus
Resting
Traces
•Asteriacites
Borings
•Bivalve Borings
Tubes
•Polychaete
Tubes

14. PhylogenyAnnelida, Polychaete
Phoronids
Arthropoda, Crustacea, Decapods
Bivalvia
Siphuncula
Echinodermata
Sea Aneamones

15. Annelids (Polychaete)

16. Phoronids

17. Arthropoda, Crustacea, Decapods

18. Bivalvia

19. Siphuncula

20. Echinodermata

21. Sea Anemone

22. 12-Rhizocorallium;
13,14-Phycodes;
16-Laevicyclus;
26-Chordites

23. 36-Gyrochorte;53-Zoophycos;57,60-Chondrites

24. 67,68-Asteriacotes;71-Gyrochorte;73-Gyrolithes

25. Classification + Description
IchnogenusPreservation
Full Relief
Hyporelief
Epirelief
Ethology
Fodinichnia
Domichnia
Cubichnia
Repichnia
Pascichnia
Trophic Type
Suspension
Feeder
Detritus
Feeder
Deposit
Feeder
Scavanger
Phylogeny

26. -Nishi Shah