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Trace Fossils or Ichnofossils
Trilobite Tracks
Trilobite Tracks
Kope Formation Ordovician
Cininnati, OH

Fossils do not always represent a part of the organism. Trace fossils record the activities of organisms. Tracks, burrows, eggshells, nests, tooth marks, gastroliths (gizzard stones), and coprolites (fossil feces) are examples of trace fossils or ichnofossils. Trace fossils represent activities that occurred while the animal was alive. Thus, trace fossils can provide clues to diet and behavior. Ichnology (ichn "trace or track, -ology "the science of") is the study of trace fossils. Trace fossils represent multiple modes of preservation but are considered here as a category for convenience.


Tracks represent animals going about their day-to-day activities and may provide insight into the dynamic behavior of extinct organisms. Tracks are formed in situ, that is they are found in the place were the organism made them. The rocks containing tracks provide clues to the environment in which the imprints were made.

Footprints making up a track can reveal the pace (steps), stride (the distance between consecutive steps made by the same foot), and trackway width or straddle. Steps and stride can reveal anatomical features, such as, number of toes or whether the organism was a biped or quadruped. Straddle can be used to measure the extent to which the animal sprawls or walks erect (Lockley & Meyer, 2000, pp3-4). Pace angulation (angle between step line segments) helps to determine the body width of an animal (Prothero, 1998, p. 413).

Mathematical relationships between stride length and hip height (measured by footprint length) of some vertebrates can help us to establish relative velocity.
In 1976 R. McNeil Alexander, a British zoologist, proposed the most widely used formula for estimating the speed of animals from their trackways where g is the acceleration due to gravity, SL the stride length, and h hip height (footprint length x 4). Relative stride length is a ratio of stride length divided by hip height. A ratio of greater than 2.0 for most terrestrial tetrapods marks the point at which an animal changes from walking to trotting. A ratio of greater than 2.9 marks the point at which an animal is running (Prothero, 1998, p. 412). Paleontologists have also attempted to use tracks as an indicator of metabolism; was the organism endothermic ("warm blooded") or ectothermic ("cold blooded")?

Trackways can provide clues to the social nature of the animal, was it gregarious (social), and did the animal travel in herds? Trace fossils can be combined to provide multiple lines of evidence. Dinosaur nesting sites and trackways support the idea that some herbivorous dinosaurs were gregarious. This same evidence may also point to migrating behavior. Tracks of multiple organisms (footprint assemblage or ichnocoenosis) combined with an analysis of rock formation can help to build an ecological picture of ancient environments. Trackways at Davenport Ranch in Texas record a herd of 23 sauropods apparently being tracked by 5 theropod dinosaurs (Prothero, 1998, p. 414)

The system for naming footprints (ichnotaxonomy) runs somewhat parallel to the taxonomy for body fossils. A track made by Tyrannosaurus would be given the formal name Tyrannosauripus. Footprint names end in -pus ("a foot"), -podus ("foot"), or -ichnus ("track or trace") (Borror, 1988, pp 47, 78, & 82). Determining who made tracks is a prime objective of tracking. Looking at body fossils from the same time period to compare foot anatomy to the track is the key. For example, Pterosaur feet (body fossils) are an excellent match for Pteraichnus (footprints).

In very rare instances the tracks are found with the maker. A specimen of Kouphichnium walchi (a horseshoe crab), found in the Solnhofen strata, is preserved at the end of its track (Boucot, 1990, p. 314). Bivalves with escape trails have been found in siderite nodules from Mazon Creek (Nudds & Selden, 2008, p. 123).

Patterns of tracks through time, known as palichnostratigraphy corresponds well with biostratigraphic zones (time intervals defined by fossils). The longevity of the average dinosaur species, defined by appearance and disappearance from the geologic record, is 7 to 8 million years. Ichnologists find essentially the same span of time, 7 to 8 million years for changes in the footprint record (Lockley & Meyer, 2000, p. 10).


The Reverend William Buckland (1784-1856), an English geologist/paleontologist, was the first scientist to recognize the true nature of fossilized feces. Buckland coined the term coprolite or "dung-stone" to describe these trace fossils. The oldest known vertebrate coprolites come from Silurian deposits and represent fish feces (Eschberger, 2000, Coprolite Article). Coprolites attributed to arthropods are known from the Ordovician (Taylor, Taylor & Krings, 2009, p. 1007).

Dr. Karen Chin, curator of paleontology at the University of Colorado Museum in Boulder identifies several criteria for coprolite identification. Coprolites often have a high calcium phosphate content (Williams, 2008, p. 47). Phosphate helps mineralize feces. This may help to explain why there is a preservation bias for carnivore coprolites over those of herbivores. Carnivore's coprolites contain their own source of phosphate in the bones and teeth of the consumed prey. Herbivorous coprolites contain the cellulose and lignin of plants and require an outside source of phosphate, usually in the form of marine sediments. The need for phosphate does not apply to all coprolite preservation unlike vertebrates, the coprolites of terrestrial arthropods, have been found in the Rhynie chert, permineralized coal balls and fossil wood (Taylor, Taylor, & Krings, 2009, pp. 1007-1011).

Shape can also be an important clue. Sharks and many primitive fish produce spiral-shaped coprolites. The shape of coprolites from larger organisms such as dinosaurs may be affected by splatting issues, trampling, weather and dung consumers. Shape can also be misleading. Salmon Creek in the state of Washington produces beautifully shaped siderite (iron carbonate) deposits, which resemble feces. These structures are sold as turtle or even ground sloth Miocene-aged coprolites. There is some debate about the nature of these deposits. Adolf Seilacher of Yale University suggests they may represent intestinal casts or cololites (Seilacher, 2001, p. 1). George Mustoe of Western Washington University points out that there is a real lack of evidence as to an animal origin for these deposits. First, they lack calcium phosphate. Second, they lack internal clues such as pollen, scales, seeds, bones or plant fibers. Third, the deposit in which they are found lacks fossils. These siderite deposits most likely do not represent coprolites. The real value in coprolites is what they contain.

Coprolite research is carried out primarily with thin sections. Herbivorous dinosaur coprolites studied by Chin have established a relationship between plant eating dinosaurs and tunneling insects related to dung beetles (Eschberger, 2000, Coprolite Article). Dr. Chin has also established that T-rex pulverized its victims from studying microscopic bone fragments found in a coprolite. Indian and Swedish scientists have found grass phytoliths in dinosaur coprolites. This helps to establish that dinosaurs and grasses coexisted (Williams, 2008, p. 51). Coprolites of arthropods recovered from rock material, such as the Rhynie chert, are composed of spores as well as plant and fungal remains (Taylor, Taylor & Krings, 2009, p. 1007). These Devonian-aged arthropods were probably detritus feeders. Coprolites provide important insight into diet, physiology as well as the geologic and geographic distribution of plants and animals.

Insect Ichnofossils

Insect ichnofossils (trace fossils) can be helpful in determining what types of insects were present at a particular time and provide information about the nature and persistence of past plant-insect associations.

Evidence for herbivory in insects appears in the Carboniferous. Like vertebrates, the first insects were carnivores and detritivores. Herbivory requires hosting cellulose-digesting bacteria through a symbiotic relationship within the gut. The oldest examples of marginal and surface feeding are on Carboniferous seed fern leaves of Neuropteris and Glosspteris (Grimaldi & Engel, 2005, p. 52). It is estimated that only 4% of the leaves in Carboniferous deposits exhibit damage from feeding. Herbivores do not make a significant impact on plant life until the Permian (Kenrick & Davis, 2004, pp. 166-167).

Galls are excessive growths on stems, leaves, cones, and flowers caused by insect feeding or egg laying. The earliest fossil galls are found on the petioles of Psaronius tree ferns of the Late Carboniferous. Insect gall fossil diversity and abundance takes off with the advent of flowering plant evolution in the Cretaceous (Grimaldi & Engel, 2005, p. 53).

Insects produce tunnels in wood known as borings or galleries. Some insects eat the cambial layer while others eat fungus that grows within the galleries, still others eat the wood itself. The oldest borings and galleries in wood, attributed to mites, are known from the Carboniferous. The first definitive beetle borings are from the Triassic. There are some borings in permineralized Triassic-aged wood from Arizona that are attributed to termites or bees; however, they may be beetle borings (Grimaldi & Engel, 2005, p. 54 & 55).

Leaf mines are meandering tunnels produced by the feeding larvae of some beetle, fly, and sawfly species. The first definitive leaf mines first appear in the leaves of Triassic conifers and pteridosperms. Interestingly, the abundance and diversity of fossil leaf mines coincides with the radiation of flowering plants (Angiosperms) during the Cretaceous. Leaf mines have been used to establish the persistence of insect and plant associations. For example, the larvae of certain moth families have been eating the leaves of Quercus (oak) and Populus (poplars) for 20 million years and hispine beetles have been eating the leaves of Heliconia for 70 million years (Grimaldi & Engel, 2005, p. 52).

Caddisfly larvae live in lakes, ponds, and rivers. Many build distinctive protective cases from bits of sand, shells and vegetation. Fossil caddisfly cases can often be identified to the family or even genus level. The oldest larval caddisfly cases (Trichoptera) are found in the Jurassic (Grimaldi & Engel, 2005, p. 51).

Celliforma is a fossil bee nest (in the form of subterranean excavations) that is first found in Late Cretaceous deposits. Celliforma is found from the Cretaceous to the Pliocene (Grimaldi & Engel, 2005, p. 51). Termite borings appear in the Cretaceous and represent the oldest undisputed fossil nest for social insects (Grimaldi & Engel, 2005, p. 54). Coprinisphaera is the fossil burrow of a scarabaerine dung beetle, which makes its first appearance during the Paleocene. Coprinisphaera lived from the Paleocene to the Pleistocene and had a wide geographic range being found in South America, Antarctica, Africa and Asia. Coprinisphaera coincide with the evolution of the first ecosystems to have abundant mammalian herbivores. Evidence for the first scarab tunnels are found in the coprolites of herbivorous dinosaurs from the Late Cretaceous of Montana (Grimaldi & Engel, 2005, p. 50).

Marine Trace Fossils

Marine Trace fossils are often classified into behavioral categories. Does the trace fossil represent resting, dwelling, crawling, grazing or some other type of feeding behavior (see Prothero, 1998, p 406 for more details)? Perhaps the most practical way to classify trace fossils is by their associations with a particular sedimentary environment or ichnofacies. In marine environments different ichnofacies are associated with different water depths, physical energies (wave & current conditions), or even type of substrate. Ichnofacies have become a standard tool for sedimentary geologists as well as paleontologists (Prothero, 1998, p. 406).

Evolutionary Trends

Trace fossils can also help to establish evolutionary trends. Deep burrows in marine sediments first appear in the fossil record during the late Precambrian and indicate the presence of soft-bodied coelomates (Prothero, 1998, p. 227). The earliest evidence for herbivory in insects appears in the Carboniferous. Specimens of Neuropteris and Glossopteris seed fern leaves have been found that show signs of marginal and surface feeding. Definitive leaf mines, which are produced only by insects with complete metamorphosis, first appear in the Triassic. The first undisputed bee nests and termite borings appear in Cretaceous deposits adding evidence to body fossils that social insects had evolved by this time (Grimaldi & Engel, 2005, pp 50-55).


Ichnofossils are important tools that help geologists interpret sedimentary environments, paleobathymetry, and provide clues to the diagenetic history of some sedimentary rocks. For the paleontologist and fossil collector ichnofossils represent fossilized behavior and provide important clues to paleoecology and paleoenvironments.
Pseudocoprolite or Cololite?
Wilkes Formation Miocene
S.W. Washington State
5.5 cm in length
Pseudocoprolite or Cololite?
Wilkes Formation Miocene
S.W. Washington State

11 cm in length
Bird Tracks
Bird Tracks
Green River Formation
Wasatch County, Utah
Plate 15 cm x 15 cm

Insect Galleries in Blue Forest Wood
Insect Galleries (White Ovals)
Blue Forest Wood
Green River Formation
Blue Forest, Wyoming

Insect Galleries in Blue Forest Wood
Insect Galleries
("Sausage" Shapes by Central Pith)
Green River Formation
Blue Forest, Wyoming


Teredolites ichnofacies
(Teredo bivalve borings in
Araucaria-like wood)
Windalia Radiolarite Formation
Middle Cretaceous
Western Australia

Crocodile Coprolite
Green River Formation
Kemmerer, Wyoming

5 cm wide x 20 cm long

A similar specimen is described by Grande (1984, p. 199).

Poplar Leaf with Insect Damage
Populus wilmattae
Green River Formation
Bonanza, Utah

Burrow of a shrimp-like organism

Larimer County, Colorado
1 cm wide x 7 cm long

Ophiomorpha cast
Burrow of a shrimp-like organism
Fox Hills Formation
Weld County, Colorado
1.5 cm wide x 2 cm long

Termite Coprolites in Permineralized Palmoxylon fiber
Catahoula Formation
Rapides Parish, Louisiana
Individual coprolites are 1mm in length


Borror, D.J. (1988). Dictionary of Word Roots and Combining Forms. California: Mayfield Publishing Company.

Boucot, A.J. (1990). Evolutionary Paleobiology of Behavior and Coevolution. New York: Elsevier

Eschberger, B. (2000). Coprolites. Suite

Garcia, F.A. & Miller, D.S. (1998). Discovering Fossils: How to Find and Identify Remains of the Prehistoric Past. Pennsylvania: Stackpole Books.

Grande, L. (1984). Paleontology of the Green River Formation, with a Review of the Fish Fauna [2nd edition]. The Geological Survey of Wyoming, Bulliten 63.

Grimaldi, D. & Engel, M.S., (2005). Evolution of the Insects. New York: Cambridge University Press.

Lockley, M. & Meyer, C. (2000). Dinosaur Tracks and Other Fossil Footprints of Europe. New York: Columbia University Press.

Nudds, J.R. & Selden P.A. (2008). Fossil Ecosystems of North America: A Guide to the Sites and Their Extraordinary Biotas. Chicago: University of Chicago Press.

Prothero, D.R. (1998). Bringing Fossils to Life: An Introduction to Paleobiology. New York: McGraw-Hill.

Seilacher, A., Marshall, C., Skinner, H.C.W., Tsuihiji, T. (2001). A fresh look at sideritic "coprolites". Paleobiology, vol 27 No. 1: 7-13.

Taylor, T.N., Taylor E.L. & Krings, M. (2009). Paleobotany: The Biology and Evolution of Fossil Plants [2nd Ed]. New York: Academic Press.

Thompson, I. (1982). National Audubon Society Field Guide to Fossils. New York: Alfred A. Knopf.

Williams, D. B., (2008) Its a Dirty Job, But Someone's Gotta Do It: Fossilized feces reveal significant details about ancient life. Earth, Sept.

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