Trace Fossils and Burrows
Trace fossils are non-body remains indicating the activity (behaviour) of
an organism. They can represent plants or animals. For example, footprints,
trails, stromatolites, coprolites (fossil feces), eggs, rhizoliths
(root-related cementation), borings, and burrows can be trace fossils.
The study of traces is known as ichnology, which is subdivided
into paleoichology (trace fossils) and neoichnology (modern traces).
Burrows are a type of trace fossil found commonly in sedimentary
rocks. They represent the activity of an organism within the sediment, after
the sediment has been deposited. Because of this temporal relationship,
burrows normally cross-cut other deposition-related sedimentary structures
like bedding and laminations. In some areas, burrowing is so extensive that
the sedimentary bedding is pervasively disrupted. The process of disruption
of deposition-related sedimentary structures is known as
bioturbation.
Burrow morphologies are amazingly diverse, and include a variety of wall structures (layered, packed with fecal pellets, lined with mud or sand),
sediment infill (sorted or not sorted, similar or different grainsizes), and
many geometries (branched tubes, subhorizontal and/or subvertical orientation,
curved tubes, U-shaped tubes, mesh geometries, cone-shaped, etc.). Geometries
composed of cylindrical shapes are by far the most common (e.g., a burrow may
be branched, but segments will most often be cylindrical).
Burrow Example
One example is insufficient to demonstrate the diversity of burrows,
but it does demonstrate their usual appearance in the rock, and the
potential for similarity to the specimens discussed in this evaluation.
Thalassinoides sp. burrow. A type of dwelling burrow (domichnia)
common in shelf marine environments. This type of burrow is probably
produced by a lobster, crayfish, or other type of burrowing crustacean,
as indicated by similar modern burrows and occasional preservation of
the crustacean within the burrow as a body fossil. The hammer is sitting
on the bedding surface. Note that the burrow is considerably flattened
perpendicular to the bedding, giving it an elliptical cross section. This
specimen is from the Upper Cretaceous Bad Heart Formation in Alberta. Photo
courtesy Chris Collom (collom@geo.ucalgary.ca).
Ophiomorpha sp. burrow. Another type of burrow produced by
crustaceans. Note the angular junction between segments of the burrow.
This example is on a bedding plane surface, so most of the burrows
are nearly horizontal. From the Upper Cretaeous Semilla Sandstone, New
Mexico, U.S.A. Modified from figure 8E of:
Nummedal, D.; Wolter, N.R.; Fleming,
T.F.; and Bergsohn, I., 1993. Lowstand, shallow marine sandstones in
Upper Cretaceous strata of the San Juan Basin, New Mexico. IN:
Caldwell, W.G.E. and Kauffman, E.G. (eds.), Evolution of the Western
Interior Basin. Geological Association of Canada, Special Paper
39, p.199-218.
Scale bar is in centimetres.
More information
Back to the evaluation of Carboniferous bone
Andrew MacRae
macrae@geo.ucalgary.ca
Thalassinoides sp. burrow. A type of dwelling burrow (domichnia)
common in shelf marine environments. This type of burrow is probably
produced by a lobster, crayfish, or other type of burrowing crustacean,
as indicated by similar modern burrows and occasional preservation of
the crustacean within the burrow as a body fossil. The hammer is sitting
on the bedding surface. Note that the burrow is considerably flattened
perpendicular to the bedding, giving it an elliptical cross section. This
specimen is from the Upper Cretaceous Bad Heart Formation in Alberta. Photo
courtesy Chris Collom (collom@geo.ucalgary.ca).
Ophiomorpha sp. burrow