Trace fossils are any indirect evidence of ancient life.  They refer to features not representing parts of the body of a once-living organism.  Traces include footprints, tracks, trails, burrows, borings, and bitemarks.  Body fossils provide information about the morphology of ancient organisms, while trace fossils provide info. about the behavior of ancient life forms.  Interpreting trace fossils and determining the identity of a trace maker can be straightforward (for example, a dinosaur footprint represents walking behavior) or not.  Sediments that have trace fossils are said to be bioturbated.  Burrowed textures in sedimentary rocks are referred to as bioturbation.  Trace fossils have scientific names assigned to them, in the same style & manner as living organisms or body fossils.



Skolithos  linearis


Skolithos linearis (Haldeman, 1840) burrows in quartzose sandstone (9.0 cm across at its widest) from the Antietam Formation (Upper Cambrian) in the Antietam area, NE of the Potomac River, southern Washington County, western Maryland, USA.

Many shallow-water quartzose sandstones have conspicuous, long, vertical burrows called Skolithos linearis.  Geologists traditionally consider  Skolithos as a burrow of a filter-feeding vermiform organism in a shallow-water, high-energy lithofacies.  Most Skolithos occurrences in the geologic record may be safely interpreted as such, but some demonstrably terrestrial examples constructed by other organisms have been recently discovered (e.g., see Martin, 2006).



Skolithos linearis burrows (cross-section view; lens-cap for scale) in quartzite (well-cemented quartzose sandstone), Clinch Quartzite, Lower Silurian; Clinch Mountain, Tennessee, USA.



Skolithos linearis burrows (plan view - small circular structures; lens cap for scale) in quartzite (well-cemented quartzose sandstone), Clinch Quartzite, Lower Silurian; Clinch Mountain, Tennessee, USA.





Fossil bird footprint (above & below; rock is 5.2 cm across) impressed on grayish-green argillaceous lime mudstone (below: sole of above slab showing underprint/undertrack).  This comes from Utah's famous Soldier Summit Fossil Track Horizon.  A persistent horizon of intensely bioturbated argillaceous lime mudstone occurs in the Eocene-aged Green River Formation near Soldier Summit (southern Wasatch County, north-central Utah, USA).  This area was once the southwestern shore of ancient Lake Uinta.  This print was made by some wading bird, probably something like a sandpiper (see Moussa, 1968).






Anchisauripus exsertus (Lull, 1904) (left) theropod dinosaur footprint from the Connecticut River Valley of eastern America (CMC public display - Cincinnati Museum of Natural History & Science, Cincinnati, Ohio, USA).

Eubrontes giganteus Hitchcock, 1845 (right) theropod dinosaur track (~30-35 cm across at its widest) in fine-grained sandstone of the Longmeadow Formation (Upper Triassic/Lower Jurassic), Mt. Tom Dinosaur Tracksite, north of Holyoke, Connecticut River Valley of Massachusetts, USA.



Apatosaurus footprint (reproduction) from the Upper Jurassic of western America (public display, Field Museum of Natural History, Chicago, Illinois, USA).



Dinosaur tracksite - dinosaur-trampled sediment surfaces are referred to as dinoturbation.  At the locality shown here, 325 dinosaur tracks made by 37 individuals are impressed on quartzose sandstones.

Stratigraphy: Dakota Sandstone, upper Lower Cretaceous.

Locality: eastern side of Dinosaur Ridge, Colorado, USA.





Diplocraterion in calcisiltite from the Arnheim Formation (lower Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician) of southwestern Hamilton County, Ohio, USA.  This is a bedding plane view of a Diplocraterion U-tube (apparently D. helmerseni or D. biclavatum).    MUGM 8099 (Karl E. Limper Geology Museum, Miami University, Oxford, Ohio, USA).

Diplocraterion is a distinctive U-tube shaped trace fossil (see cross-section view).  In bedding plane view, it is often a dumbbell-shaped structure.  It is moderately common in the Upper Ordovician fossiliferous limestone-shale succession of southwestern Ohio, southeastern Indiana, and northern Kentucky (the Cincinnatian Series).  U-tubes having parallel sides have been called Diplocraterion parallelum.  U-tubes having a flared base have been called Diplocraterion helmerseni.  Specimens having a pair of blind pouches at the bottom of the U-tube have been called Diplocraterion biclavatum.





Asteriacites on underside of very fine-grained quartzose sandstone (rock is 7.0 cm across), unrecorded Pennsylvanian-aged stratigraphic unit from an undisclosed locality in Kansas, USA.

Asteriacites is one of the most distinctive invertebrate trace fossils around.  Asteriacites is a burrow made by a starfish (Phylum Echinodermata, Class Asteroidea) or brittle star (Phylum Echinodermata, Class Ophiuroidea).  The specimen shown here is a convex hyporelief on the underside of a very fine-grained sandstone from Kansas.  Fine striations along the impressions of the arms represent digging motions by the tube feet.  Even the depression in the mouth area shows scratches (not really visible in this photo) made by movements of the mouth frame.



Fustiglyphus annulatus


Fustiglyphus annulatus specimen from the Arnheim Formation (lower Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician) at Lanes Mills, Oxford, southwestern Ohio, USA.  MUGM 8098 (Limper Geology Museum, Miami University, Oxford, Ohio, USA).

One of the stranger trace fossils described in the literature is Fustiglyphus (often misidentified as Rhabdoglyphus).  It's a relatively narrow, parallel-sided burrow with significant swellings at semi-regular intervals.

Making sense of this burrow type has been difficult (see Osgood, 1970).  The burrow is inferred to be entirely infaunal, despite its common presence at weathered-out bedding planes.  The Fustiglyphus maker appears to have preferred burrowing at sediment interfaces (silt-mud interfaces, sand-mud interfaces, etc.).  What specific behavior generated the swellings is unclear.  The modern snail Illyanassa has been observed occasionally excavating a shallow depression along its locomotion trails, but those are epifaunal traces.





Crocodilian claw scratch marks in the Dakota Sandstone (upper Lower Cretaceous), eastern Dinosaur Ridge, Colorado, USA.





Daemonelix burrows (above & below) - “Devil’s corkscrews” from a paleosol in the Harrison Formation (upper Middle Miocene) in Sioux County, northwestern Nebraska, USA.

This distinctive spiral burrow was made by an ancient species of terrestrial beaver.  The spiraled portion of these trace fossils is usually about 1.5 to 2 meters tall.  The base of the spiraled portion merges with a subhorizontal tube.  The burrow filled with siliciclastic sediments that was better cemented compared with surrounding materials.

Above: reproduction on public display, Field Museum of Natural History, Chicago, Illinois, USA.

Below: vintage field photo of excavated Daemonelix burrows in a Harrison Formation paleosol in what is now Agate Fossil Beds National Monument (original photo: University of Nebraska; photo provided here courtesy of Agate Fossil Beds National Monument).



Some references:


Moussa (1968) - Journal of Paleontology 42(6): 1433-1438.


Osgood (1970) - Trace fossils of the Cincinnati area.  Palaeontographica Americana 6(41): 369-371, 433, pl. 78.


Häntzschel (1975) - Trace fossils and problematica.  Treatise on Invertebrate Paleontology, Part W, Miscellanea, Supplement 1.  pp. 63, 64, 98-101.


Stanley & Pickerill (1998) - Systematic ichnology of the Late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada.  Royal Ontario Museum Life Sciences Contributions 162.  55 pp.


Martin (2006) - Trace Fossils of San Salvador.  San Salvador, Bahamas.  Gerace Research Center.  80 pp.


Home page