Coprolites are fossilized feces, a type of trace fossil that provides evidence of an ancient organism’s behavior rather than its physical body structure. These rare “dung stones” offer a unique window into the diets, ecosystems, and life habits of creatures that lived millions of years ago. By studying the composition and contents of coprolites, scientists can reconstruct ancient food webs and environments that existed during the animal’s lifetime. This analysis allows researchers to piece together a more complete picture of prehistoric life.
Defining True Coprolites
A true coprolite is a petrified mass of excrement that has undergone a specific fossilization process, replacing the original organic material with minerals such as silicates or calcium carbonates. This process, known as lithification, requires the fecal material to be buried rapidly and protected from decomposition, often in an environment lacking oxygen. The presence of high levels of calcium phosphate, a mineral abundant in bone, is a strong chemical indicator that a specimen is a true coprolite, particularly from a meat-eating animal.
It is important to distinguish true coprolites from other geological finds that may look similar. Pseudocoprolites are inorganic concretions—mineral formations that acquire a fecal-like shape but are not biological in origin. Gastroliths, or “stomach stones,” are another distinct finding, representing stones swallowed by an animal to aid in digestion. True coprolites are identified by structural patterns like spiral markings, or by the presence of undigested fragments of food and internal parasites.
Categorization Based on Diet
The primary classification of coprolites is based on the producer’s diet, determined by the contents preserved within the fossilized mass. This provides direct evidence of what a specific organism consumed during a single meal. Analyzing these types allows paleontologists to infer the animal’s feeding strategy and trophic level.
Carnivore/Piscivore Coprolites
Carnivore coprolites are rich in calcium phosphate and often contain identifiable fragments of prey. These specimens reveal crushed bone fragments, teeth, fish scales, or muscle tissue, demonstrating the animal was a predator or scavenger. Marine carnivores, such as ancient sharks, produced coprolites that often feature a distinct spiral or corkscrew shape, mimicking the structure of their spiral valve intestine. The discovery of a large Tyrannosaurus rex coprolite containing bone fragments confirmed its bone-crushing feeding habits.
Herbivore Coprolites
Coprolites from herbivores are more rounded or amorphous in shape and are characterized by a high concentration of plant matter. Analysis of these fossils reveals partially digested plant tissues, seeds, bark, roots, and pollen grains. Microscopic examination of plant cuticles and phytoliths—tiny silica structures from plant cells—can identify the exact species of flora consumed. Herbivore coprolites are less common because their composition contains fewer minerals needed for successful fossilization compared to the calcium-rich feces of carnivores.
Omnivore Coprolites
Omnivore coprolites display a mixed composition, containing both animal and plant remains, reflecting a varied diet. In archaeological contexts, these are often associated with prehistoric human activity, known as paleofeces. For example, Neanderthal coprolites have shown traces of both meat and significant amounts of plants, indicating a broader diet than previously assumed. Chemical analysis of molecular biomarkers, such as certain steroids, helps confirm an omnivorous diet by identifying components indicative of both plant and animal consumption.
Scientific Insights from Contents
The analysis of coprolite contents provides extensive data, making these fossils archives of ancient life. Reconstructing paleo-diets is the most direct application, with the remains of undigested food offering a precise snapshot of a single meal. Scientists use stable isotope testing on the fossilized material to determine the animal’s position in the food chain and distinguish between different types of plants, such as those using C3 or C4 photosynthesis. This chemical data complements the physical evidence of scales, bones, or seeds found in the coprolite.
Paleoparasitology, the study of ancient parasites, relies heavily on coprolites, which often contain well-preserved eggs and larvae of intestinal worms. Identifying these microscopic parasites provides direct evidence of the diseases that affected ancient human and animal populations. Analyzing parasite types in human coprolites can reveal dietary variations between different ancient communities, such as those who primarily ate fish versus those who consumed maize.
The study of preserved pollen grains within coprolites offers a detailed way to determine the past environment, or paleoenvironment, where the animal lived. Since pollen is durable and distinctive, its presence indicates which plants were growing in the habitat at the time the coprolite was deposited. This analysis helps reconstruct ancient ecosystems, including information about water sources and climate conditions, which is useful when reconstructing the habitats of animals whose body fossils are not present.