TRACE FOSSILS
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 TRACK
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).
DINOSAUR TRACKS
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
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
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
Crocodilian claw scratch marks in the Dakota Sandstone (upper Lower Cretaceous),
eastern Dinosaur Ridge, Colorado, USA.
DEVIL'S CORKSCREW
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.