Trace fossils

Trace fossils record what animals did (resting, crawling, feeding, dwelling and escaping) rather than their bodies. They're named as ichnogenera, which say nothing about who made them, and they're rarely transported, so they record conditions where they formed.

Ichnogenera

Behavior (ethology) classes

Class	Behavior	What it looks like
Cubichnia	Resting	Shallow depressions that often preserve the resting animal's body shape.
Repichnia	Locomotion	Linear to sinuous trackways or trails parallel to bedding.
Pascichnia	Grazing	Surface feeding traces parallel to bedding that rarely cross themselves.
Fodichnia	Feeding	Burrows where animals processed sediment for food, often mostly horizontal.
Domichnia	Dwelling	Homes below the surface, often U-shaped or branching and commonly perpendicular to bedding.
Agrichnia	Farming	Geometric burrow systems used to grow bacteria or algae for food.
Fugichnia	Escape	Vertical movement to escape burial, often nested or stacked.
Equilibrichnia	Equilibrium	Vertical adjustment to stay level with a rising (or eroding) sediment surface.
Praedichnia	Predation	Bite marks, borings and repaired shells from predation.

Ichnofacies

Recurring groups of traces that track environment, mainly water depth, energy, oxygen and substrate. Adolf Seilacher developed the concept in 1967.

Trypanites	Hardgrounds: rocky coasts, beachrock, reefs, bone beds, coquina. Borings are the only traces; bioerosion is the key process.
Glossifungites	Firmgrounds: compacted, dewatered mud or sand later exhumed by erosion, in shallow to deep water. A mix of relict and overprinted traces.
Teredolites	Woodgrounds: wood clasts, log jams, peats and coals, mostly in estuaries, delta plains and back-barrier areas.
Psilonichnus	Supralittoral to upper littoral, moderate to low energy: beach backshores, dunes, washover fans, supratidal flats. Mixes terrestrial traces with marine burrowers such as crabs.
Skolithos	Shifting, well-sorted sand in the littoral zone under moderate to high energy: beach foreshores and shorefaces; also estuarine point bars, tidal deltas and deep-sea fan sands.
Cruziana	Moderate- to low-energy offshore settings: shelves and epeiric seas, and quieter parts of estuaries, bays, lagoons and tidal flats.
Zoophycos	Quiet water from restricted littoral to bathyal settings, typically offshore below storm wave base, often oxygen-deficient.
Nereites	Bathyal to abyssal settings with slow pelagic/hemipelagic deposition, sometimes interrupted by turbidites.
Scoyenia and Mermia	Continental (non-marine) ichnofacies.

**Skolithos ichnofacies.** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Cruziana ichnofacies.** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Zoophycos ichnofacies.** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Nereites ichnofacies.** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Scoyenia ichnofacies (continental).** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Mermia ichnofacies (continental).** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Substrate-dependent ichnofacies (Glossifungites, Trypanites, Teredolites).** Page C. Quinton via Wikimedia Commons, CC BY-SA 4.0. Source

**Behavior examples: Nereites, Diplichnites, a predatory drill hole, Asteriacites.** Richdebtomdom (CC BY-SA 3.0); Michael C. Rygel (CC BY-SA 4.0); Jonathan R. Hendricks (CC BY-SA 4.0); Mark Wilson (public domain). Source

Photos are hosted by their original sites and shown under their open licenses (CC BY, CC BY-SA, public domain or Open Government Licence). Click a photo for its source page.

Traces through time

The first appearance of Treptichnus pedum marks the base of the Cambrian, about 539 million years ago.
Cruziana and Rusophycus appear in the earliest Cambrian and persist into the Triassic, after trilobites were gone.
Skolithos: Early Cambrian to present. Zoophycos: Early Ordovician to present, moving from deep water (Silurian) to nearshore (Devonian–Permian) and back to deep water today.
Thalassinoides becomes abundant at the start of the Mesozoic; Ophiomorpha ranges from the Early Permian and is prominent from the Jurassic.
Paleodictyon: Precambrian/Early Cambrian to the present, in the deep sea.

Sources

Rygel & Quinton, Sedimentary Geology 9.6: Trace Fossils · KU Ichnology: Ichnofacies models · Wikipedia: Trace fossil · Wikipedia: Treptichnus · Wikipedia: Cruziana · Wikipedia: Rusophycus · Wikipedia: Skolithos · Wikipedia: Zoophycos · Wikipedia: Thalassinoides · Wikipedia: Ophiomorpha · Wikipedia: Paleodictyon