This is a serious subject, so no joking around here. Professor Chin says
Under exceptionally favorable conditions, ancient feces have been preserved as fossils called coprolites. Because feces are largely composed of soft material, coprolites are usually much rarer than skeletal fossils. They can be locally abundant, however, and such concentrations contributed to early interest in these unusual formations. The first published report of fossil feces actually predates the earliest descriptions of dinosaur bones and was made without benefit of precedent when William Buckland compared some enigmatic white fossil lumps with fresh hyena feces and deduced a fecal origin (1823). He later (1835) applied the term 'coprolite' to fossilized feces.
Coprolites have been found on every continent, with the oldest known vertebrate specimens dating back to the Silurian (Gilmore, 1992). Although some Quaternary feces have been preserved through desiccation and resemble modern dried dung (e.g. Mead and Agenbroad, 1992), most coprolites have been substantially altered during fossilization. A small number of specimens have been preserved as carbonaceous compressions (e.g. Hill, 1976), but the overwhelming majority of
coprolites are lithified.
Most fossil feces have been recognized by their familiar fecal shapes, but coprolites are highly variable fossils. This variation reflects differences in the animals that produced the feces, fluctuations in diet, and disparate diagenetic conditions. Numerous coprolite morphologies have been described, including spherical, cylindrical, fusiform, spiral, blocky, pancake-like, and amorphous forms. This
range of shapes is similar to that found in modern animal droppings. The colors of coprolites also vary considerably: different diagenetic regimes have resulted in brown, white, cream, orange, black, gray, and even bluish specimens.
As trace fossils, coprolites provide a record of animal activity, and have the potential to supplement information obtained from skeletal fossils. Although coprolitic interpretations are complicated by diagenetic variability, well-preserved specimens can contain recognizable dietary inclusions that provide information on trophic interactions in ancient ecosystems. This information can be enhanced by some knowledge of the animal of origin.
Coprolite Provenance
The assignment of a coprolite to its source animal remains one of the more difficult problems of coprolite analysis. Unless a formed but unextruded fecal mass is found in the body cavity of an articulated specimen, its origin remains speculative. There are certain factors, however, that can help constrain a list of likely producers.
A spiral configuration is the only distinctive coprolite morphology that can be reliably associated with a type of source animal. Primitive fishes have spiral intestinal valves that effect the egestion of coiled feces. Because the spiral valve is absent in teleosts and tetrapods (Romer and Parsons, 1986), spiral coprolites are attributable to primitive fish such as sharks, gars, or lungfish (Gilmore, 1992).
Spiral coprolites have been recovered from many Paleozoic and Mesozoic localities (Hantzschel et al., 1968). The widespread distribution of these specimens indicates that feces deposited in aquatic environments have a high preservation potential. This suggests that many non-spiraled coprolites may have also been produced by aquatic animals or by terrestrial vertebrates that defecated in or near bodies of water. Although non-spiraled coprolites can have distinctive shapes and/or striations, such morphologies are found in feces produced by many different taxa (Thulborn, 1991; Hunt et al., 1994). This necessitates the evaluation of non-morphological characters. Of prime consideration is the fact that the stratigraphic distribution of potential source animals must be consistent with the age, locality and depositional environment of the coprolite itself. The co-occurrence of skeletal elements in the same sediments may pose strong arguments for associations between coprolites and source animals, but such associations remain speculative without additional evidence.
Coprolite size can provide information on possible animal producers, but interpretations of the significance of size must be made carefully. Although the quantity of egested feces is proportional to
body size, direct correlations can be misleading. A small coprolite, for example, may have broken off a larger fecal mass. In addition, because some large extant animals produce quantities of small pelletoid feces, it is possible that an isolated pelletoid coprolite could have been produced by a relatively large animal. Small animals, on the other hand, cannot produce large fecal masses. These considerations suggest that coprolite size should be primarily used to infer minimum sizes of possible producers. This criterion is thus particularly useful for identifying possible dinosaur coprolites.
Coprolite composition can also help constrain the number of likely producers by providing clues to the feeding strategies of source animals. Inclusions of bone fragments, teeth, fish scales, or mollusc
shells, for example, provide evidence of carnivory. Unfortunately, recognizable dietary residues have often been destroyed by digestion and diagenesis. In such cases, carnivory can be implicated by a
predominance of calcium phosphate. Bradley (1948) noted that most coprolites are phosphatic andthat carnivore feces contain relatively high percentages of phosphorus. He suggested that carnivore feces are preferentially fossilized because of the availability of dietary calcium phosphate. This isconsistent with the observation that permineralized coprolites containing substantial plant material are
relatively rare and are almost invariably calcareous or siliceous.
Although it is difficult, if not impossible, to ascertain the origin of a coprolite, the concomitant analysis of stratigraphic occurrence, morphology, size, and composition can help characterize likely source
animals. The informative value of these factors is variable, however. The identities of some coproliteproducers may remain poorly resolved if coprolite specimens have very common features, whereas unusual or distinctive attributes might provide significant clues to coprolite provenance.
Dinosaur Coprolites
Many coprolites have been found in Mesozoic sediments, but few described specimens have been confidently attributed to dinosaurs. The identification of possible dinosaur coprolites is complicated by the fact that dinosaurs shared Mesozoic ecosystems with many other animals.
This means that non-spiraled small or mid-sized phosphatic coprolites might be particularly difficult to identify since they could have been produced by a number of carnivorous vertebrates--including fish
without spiral valves, turtles, crocodilians, or dinosaurs. Very large coprolites may be morereasonably ascribed to dinosaurs, but sizable bona fide coprolites are rare. The paucity of large specimens probably reflects preservational biases: large fecal masses would have been highly susceptible to mechanical disruption, and large animals may have rarely defecated in depositional environments that were conducive to the fossilization of feces.
These considerations help account for the poor record of dinosaur coprolites. Moreover, some specimens previously interpreted as dinosaur feces must be re-evaluated, such as those from the
Bernissart Iguanodon Quarry in Belgium. Bertrand (1903) initially attributed those coprolites totheropods, but a subsequent discussion (Abel, 1935) suggested that the feces could have been produced by crocodiles. In another report, Matley (1939) used size criteria to assign large Cretaceous coprolites from India to titanosaurs whose bones were found in the same sediments. The coprolites were probably not produced by herbivores, however, because the specimens are
phosphatic and contain no traces of plant tissue. The large droppings are up to 10 cm wide and 17 cm long, and certainly implicate hefty source animals, but it is not clear if fecal masses produced by
large carnivorous dinosaurs can be distinguished from those left by large crocodilians.
Still other purported dinosaur feces may not be coprolites at all. Large, bulbous, siliceous nodules commonly found in Jurassic deposits have sometimes been interpreted as dinosaur coprolites (Spendlove, 1979). These specimens, however, lack organic inclusions or other positive evidence that supports a fecal origin, and may simply be inorganic concretions.
The origin of large Mesozoic plant-filled coprolites is less ambiguous, because few large herbivores co-existed with dinosaurs. One unusual grouping of over 250 compressed pellets containing plant
cuticle was found in Jurassic sediments in England (Hill, 1976). The individual pellets are small (8 to 18 mm diameter), but the total assemblage represents a sizable fecal mass that could have been
produced by a herbivorous dinosaur. Much larger herbivore coprolites found in Montana are undoubtedly dinosaurian. These large (up to 24 x 33 x 34 cm) blocky Cretaceous specimens contain conifer stem fragments. They lack a familiar coprolite shape, but a fecal origin has been corroborated by the presence of backfilled dung beetle burrows in the specimens (Chin and Gill, in press).
The recognition of atypical coprolitic masses suggests that additional dinosaur droppings may be identified with more careful examination of Mesozoic sediments. Continued analyses of dinosaur feces will increase our understanding of dinosaur diets and their interactions with other organisms because coprolites can provide paleobiological information that is unavailable from skeletal fossils.
References
Abel, O. 1935. Vorzeitliche Lebensspuren. Fischer, Jena, 644 pp.
Bertrand, C.E. 1903. Les Coprolithes de Bernissart. I. partie: Les Coprolithes qui ont été attribués aux Iguanodons. Memoires du Musee royal d'histoire naturelle de Belgique 1(4):1-154.
Bradley, W.H. 1946. Coprolites from the Bridger Formation of Wyoming: their composition and microorganisms. American Journal of Science 244:215-239.
Buckland, W. 1823. Reliquiae Diluvianae. Reprint of the 1823 ed. published by J. Murray, London, 1978. Arno Press, New York, 303 pp.
Buckland, W. 1835. On the discovery of coprolites, or fossil faeces, in the Lias at Lyme Regis, and in other formations. Transactions of the Geological Society of London series 2, 3(1):223-236.
Chin, K. and Gill, B.D. in press. Dinosaurs, dung beetles, and conifers: participants in a Cretaceous food web. Palaios.
Gilmore, B.G. 1992. Scroll coprolites from the Silurian of Ireland and the feeding of early vertebrates. Palaeontology 35(2):319-333.
Hantzschel, W., El-Baz, F., and Amstutz, G.C. 1968. Coprolites, an annotated bibliography. Memoir 108, Geological Society of America, Colorado, 132 pp.
Hill, C.R. 1976. Coprolites of Ptiliophyllum cuticles from the Middle Jurassic of North Yorkshire. Bulletin of the British Museum (Natural History), Geololgy 27:289-294.
Hunt, A.P., Chin, K. and Lockley, M.G. 1994. The palaeobiology of vertebrate coprolites; pp. 221-240 in S.K. Donovan, (ed.), The Palaeobiology of Trace Fossils. John Wiley & Sons,
Chichester.
Matley, C.A. 1939. The coprolites of Pijdura, Central Provinces. Records of the Geological Survey of India 74(4):530-534.
Mead, J.I., and Agenbroad, L.D. 1992. Isotope dating of Pleistocene dung deposits from the Colorado Plateau, Arizona and Utah. Radiocarbon 34(1):1-19.
Romer, A.S. and T.S. Parsons. 1986. The vertebrate body. Saunders College Publishing, Philadelphia, 679 pp.
Spendlove, E. 1979. Henry Mountain coprolites. Rock and Gem 9: 60-64.
Thulborn, R. A. 1991. Morphology, preservation and palaeobiological significance of dinosaur coprolites. Palaeogeography, Palaeoclimatology, Palaeoecology 83:341-366.
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