View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002variable. Although we know that spiral coprolites(or intestinal casts; see Williams, 1972) wereproduced by one of the groups of fish with spiralintestinal valves (e.g., sharks, lungfish, or gars;Gilmore, 1992), morphology usually provides littleinformation about the animal of origin becausemany animal droppings produced by different taxaare quite similar. Coprolite contents, composition,size, and stratigraphic placement can, however,constrain the number of likely perpetrators.Carnivore coprolites are usually easy todifferentiate from herbivore coprolites becausethey are typically phosphatic and often containskeletal inclusions. Coprolite size is also veryinformative, since fecal volumes generally scalewith animal size. While fecal amounts are variable,it’s clear that small animals cannot produce largeindividual fecal deposits. Field guides to modernscat provide analogs that can be used to roughlyapproximate the size range of animals that producefeces of a given mass. Thus, even when the taxa offecal producers are unknown, carnivore coprolitesprovide evidence that predators of an approximatesize range frequented a given habitat. This indicatesa trophic niche that may be further defined bydietary residues that reveal prey selection patterns.In many cases, inclusions within a coproliteprovide more information about prey animals thanabout the coprolite producer itself. The integrityof included digestive residues depends on theircomposition and the extent of their exposure todigestive and diagenetic processes. Somecoprolites contain no recognizable inclusions, butrefractory skeletal constituents have been found innumerous carnivore coprolites (e.g., Hantzschel etal., 1968). When dietary residues are incompletelydigested, the morphology of elements such asmollusk shells, ganoid scales, and small bones mayallow identification of prey. Specific taxa ofmollusks (e.g., Speden, 1969; Stewart andCarpenter, 1990), crustaceans (Bishop, 1977; Sohnand Chatterjee, 1979), fish (e.g., Zangerl andRichardson, 1963; Waldman, 1970; Coy, 1995),reptiles (e.g., Parris and Holman, 1978), andmammals (e.g., Martin, 1981; Meng et al., 1998)have been recognized in coprolites. Furthermore,fragments of larger bones may be ascribed tohigher-level taxonomic groups on the basis ofhistological analysis (e.g., Chin et al., 1998).Coprolites may also show signs of ingested softtissues as organic residues or in the form of threedimensionalimpressions. Some exceptionalspecimens have revealed evidence of feathers(Wetmore, 1943), fur (Meng and Wyss, 1997),insect exoskeletons (Northwood, 1997), andmuscle tissues (Chin et al., 1999). Such remarkablepreservation requires depositional conditions thatminimize diagenetic recrystallization.These studies show that coprolites may containdietary residues that provide concrete evidence ofancient carnivory. It is clear, though, that thechallenges of coprolite analysis stem from thedifficulties involved in determining the animal oforigin and in identifying residual dietarycomponents. This analytical complexity reflects thefact that coprolites are relatively anonymouspackages that represent varying diets, digestiveprocesses, and diagenetic alteration. Such markedvariability necessitates that care be exercised indrawing conclusions from a limited number ofsamples. Even so, coprolites provide cumulativeclues that help flesh out our understanding ofpatterns of predation in ancient environments byidentifying prey species within a givenpaleoecosystem, and by indicating general size and/or age classes of prey animals (e.g., Zidek, 1980;Martin, 1981). The composition and integrity ofthese inclusions may also provide information aboutthe diet and digestive processes of the predator itself.COPROLITE ANALYSISDocumentation.—Both destructive and nondestructivetechniques may be used to analyzecoprolites, and the choice of analytical methoddepends on the questions addressed by the researchproject. Regardless of experimental approach, eachstudy of coprolites must include carefuldocumentation of provenance and of the physicalcharacteristics of each specimen.The collection of coprolites is similar to thecollection of vertebrate fossils where documentation44