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).

Coprolites

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).

Conclusion

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

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