Ichnology: The Study of Trace Fossils
Study of trace fossils (biogenic sedimentary structures)
Ichnofabric & bioturbation: degree of overturning of sediment by organisms. Excessive biological
activity obliterates individual trace fossils and sedimentary structures, mixing layers, etc.
Ichnotaxonomy: by tradition, individual trace fossil forms are given "ichnogenus" and
"ichnospecies" (and "ichnofamily" and so on) names, even though they do NOT in reality represent
a nested hiearchy based on patterns of descent!! Two trace fossils represent the same ichnospecies
if they are identical in form regardless of whether they are made by the same species or
different species; additionally, the same species can produce many different ichnospecies depending
on its behavior, the substrate, etc.
- By Behavior:
- Cubichnia: resting
- Domichnia: dwelling
- Fugichia: escape traces
- Repichnia: moving
- Paschichnia: grazing
- Agrichnia: farming
- Fodinichnia: Deposit feeding (3-D)
Ichnofacies: set of trace fossils associated with a particular set of environmental
conditions. Form excellent record of paleoenvironment, esp. as many ichnogenera persist for
hundreds of millions of years! Some major ichnofacies:
- Skolithos: Rapidly moving sediment, made by filter
- Cruziana: Shallow marine, between low tideline and storm wave base
- Zoophycos: Low energy muds and muddy sands, dysaerobic and organic
- Nereites: Deep water (associated with turbidites and pelagic muds)
itself is one of many complex surface pascichnia or fodinichnia
a series of hexagonal structures.
Builder unknown, but deep sea submersibles have found
Paleodictyon is still being formed in the abyssal realm!
- Other zones are less significant
Terrestrial trace fossils:
Both arthropod and vertebrate trackways are common. Unlike marine ichnofossils, repichnia
dominate by orders of magnitude. However, some domichnia present:
- Termite burrows
- Rodent burrows (such as Daemonelix)
Also, feeding traces can be found as bite marks on bones or leaves, and there are the occasional
study of coprolites,
and eggs and nests.
Some aspects of terrestrial (primarily vertebrate (primarily locomotory)) ichnology:
- Relatively good at identifying trackmakers: perhaps not to the genus/species level, but often
easier to resolve than marine ichnites:
- In part because vertebrates have individual footfalls
- In part because vertebrate diversity is generally lower than invertebrates (bigger, rarer
- However, there have been some famous mistakes (such as identifying limulid (horseshoe crab)
tracks as pterosaurs, or pterosaur tracks as crocodilians)
- Relatively good ability to reconstruct aspects of locomotion
- Individual attributes, such as size and stance of the animal
- Dynamic attributes, such as
pace angulation and stride length
- From some basic mechanics, and by comparison with modern animals, one can estimate
- Can occasionally get estimates of other behaviors. For example,
this one is REALLY cool: an
apparent record of
a large carnivorous dinosaur (Acrocanthosaurus or a close relative)
attacking a large herbivorous dinosaur (Sauroposeidon or a close relative) in the
Early Cretaceous of Texas. Note the "right-left-right-right-left-right" sequence in the
carnivore's steps: one hypothesis is that the predator was grabbing onto the herbivore, and
was dragged for a step before being dislodged.
hominin tracks from Laetoli, Kenya.
pterosaur ptracks from Crayssac, France.
An important thing to remember is that an ichnite is the fossil of the animal while alive,
not after it was dead!
Last modified: 19 August 2016