GEOL 331/BSCI 333 Principles of Paleontology

Fall Semester 2022
Ichnology: The Study of Trace Fossils

Assorted trace fossils on the underside of a slab of Cambrian Gros Ventre Formation of Wyoming

Key Points:
•Ichnology is the study of trace fossils.
•Ichnotaxonomy is the nomenclature of trace fossils. By tradition, every distinct trace fossil has its own ichnospecies and ichnogenus, independent of the taxonomy of the trackmaker.
•Another parallel ichnotaxonomy is a system based on the behavior represented by the fossil.
•Yet another set of descriptors are ichnofacies: a set associated ichnofossils that characterize particular environmental settings.

"No one can pass through life, any more than he can pass through a bit of country, without leaving tracks behind, and those tracks may often be helpful to those coming after him in finding their way." --1940 letter by Robert Baden-Powell, founder of scouting

Ichnology: Study of trace fossils (biogenic sedimentary structures). Ichnite: general term for a trace fossil.

An important distinction to remember is that every mark made by an organism (or fossil) is necessarily a trace fossil. It could simply be a tool mark (for instance, by a shell being bounced around in a current).

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 hierarchy 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.

Other Ichnonomenclature:

Terrestrial trace fossils:
Both arthropod and vertebrate trackways are common. Unlike marine ichnofossils, repichnia dominate by orders of magnitude. However, some domichnia present:

Also, feeding traces can be found as bite marks on bones or leaves, and there are the occasional resting tracks.

Some aspects of terrestrial (primarily vertebrate (primarily locomotory)) ichnology:

Alimentary Canal Trace Fossils

There is (whoa, surprise!) a special set of terms for ichnites associated with the digestive tract (collectively bromalites):

An important thing to remember is that an ichnite is the fossil of the animal while alive, not after it was dead!

To Syllabus.

Last modified: 6 September 2022

Dinosaur footprints at the Mill Canyon Dinosaur Tracksite, Utah