Coprolite

The scientific recognition of coprolites began in early nineteenth-century England. In the mid-1820s, Mary Anning, the renowned fossil collector of Lyme Regis on England's Dorset coast, noticed that certain peculiar stone objects were repeatedly found within the ribcage or near the pelvic region of the ichthyosaur skeletons she excavated from the Early Jurassic Lias formations. When she broke these objects open, they sometimes contained fossilized fish bones, scales, and the remains of smaller ichthyosaurs. Anning concluded that they were fossilized feces—a deduction that proved correct.

William Buckland, an English geologist already famous for describing the first validly named dinosaur genus (Megalosaurus), had independently been studying fossilized carnivore droppings since 1822, when he investigated cave deposits at Kirkdale in Yorkshire that he identified as preserved hyena dung. To test his hypothesis, he collected spotted hyena feces and commissioned chemical analyses, prompting an analyst to remark that 'it may be well for you and me not to have the reputation of too frequently and too minutely examining faecal products.' He also injected cement into the intestines of fish to record fecal morphology. When Anning provided him with her Lyme Regis specimens, Buckland recognized their fecal origin and read his findings before the Geological Society of London in 1829. The paper, formally published in the Society's Transactions in 1835, coined the term 'coprolite' and explicitly credited Anning for her discoveries and deductions.

Across the Atlantic, Congregationalist minister and Amherst College professor Edward Hitchcock found what he believed to be bird coprolites at track sites in Massachusetts in the 1840s (Hitchcock never accepted that the tracks he studied were made by dinosaurs rather than birds). Chemical analysis confirmed their fecal origin, and Hitchcock celebrated the finding as a 'scientific miracle.'

By the 1840s, coprolites had acquired economic significance. Vast coprolite deposits around Cambridge, England, were mined for their phosphate content and ground into fertilizer. The industry employed thousands and extracted an estimated two million tons by 1909. The town of Ipswich retains a 'Coprolite Street' as a testament to this period.

Feces are intrinsically ephemeral. Weathering, trampling, microbial decomposition, and coprophagy (consumption of feces by other organisms, including dung beetles) destroy most excrement rapidly. For fossilization to occur, feces must be buried quickly or desiccated before significant decay sets in.

Mineralization is the primary preservation pathway. Calcium phosphate, derived mainly from digested bone, serves as the chief mineralizing agent. According to Karen Chin, curator of paleontology at the University of Colorado Museum, hardening can begin in less than two weeks under favorable conditions. Because carnivore feces contain abundant phosphate from the bones of consumed prey, they self-mineralize and are consequently far more common in the fossil record than herbivore coprolites. Herbivore coprolites require an external phosphate source—such as marine sediments—for preservation, making them substantially rarer.

Morphology varies with the producer's body size and digestive anatomy. Primitive fishes such as sharks and lungfish possess a spiral valve in the intestine, producing characteristic spiral coprolites that can preserve exquisitely. Large dinosaur feces, deposited from a considerable height, likely splatted upon impact and seldom retained a distinct shape, which partly explains the rarity of well-formed large dinosaur coprolites.

Tyrannosaurus rex Coprolite (Saskatchewan, Canada, 1998):

Karen Chin and colleagues reported in Nature (1998) the discovery of a 44-cm-long (approximately 1.5 feet) coprolite from the Maastrichtian of Saskatchewan that could only have been produced by a very large carnivorous dinosaur—with T. rex being the only known candidate at that site. The specimen was composed of 30–50% bone fragments, many crushed to sand-grain size. This provided the first direct physical evidence that T. rex could pulverize and digest substantial quantities of solid bone, corroborating biomechanical analyses of its massive skull and bite force. Mark Norell of the American Museum of Natural History has noted ongoing efforts to conduct high-resolution CT scanning of tyrannosaur coprolites to identify the specific prey species consumed.

Maiasaura Coprolites (Two Medicine Formation, Montana/Wyoming):

Karen Chin's research on approximately 77-million-year-old coprolites from the Two Medicine Formation, roughly basketball-sized, identified them as the product of the hadrosaur Maiasaura, based on associated bones and eggshells. Herbivore coprolites are uncommon, but these specimens were doubly unusual: they contained wood tissue, a dietary component no paleontologist had previously suspected for any dinosaur. Additionally, dung beetle burrows were found within the coprolites, providing direct evidence of ancient coprophagous insect communities and demonstrating a tightly linked ecological relationship between dinosaurs and invertebrates.

Triassic–Early Jurassic Coprolite Analysis (2024):

A large-scale study published in Nature in 2024 by researchers at Uppsala University analyzed hundreds of coprolites and digestive contents from the Late Triassic through Early Jurassic, reconstructing how dinosaur food webs shifted as dinosaurs rose to ecological dominance. This represents the most comprehensive coprolite-based reconstruction of ancient food web dynamics to date.

Thin Section Microscopy:

The foundational technique in coprolite research involves cutting thin slices of the specimen and examining them under polarized light microscopy. This reveals pollen grains, spores, phytoliths (silica bodies from plants), bone fragments, muscle tissue, bacteria, and other microinclusions that identify dietary components.

Chemical Analysis:

X-ray fluorescence (XRF) and electron microprobe analysis measure phosphate and calcium concentrations, which serve as the primary criteria for confirming fecal origin. Elevated calcium phosphate distinguishes genuine coprolites from superficially similar geological concretions.

Computed Tomography (CT):

Non-destructive CT scanning reveals the three-dimensional internal structure of coprolites, including the distribution, size, and orientation of bone fragments and voids. This technique is increasingly used for large, scientifically valuable specimens where destructive sectioning is undesirable.

Synchrotron Imaging:

High-intensity synchrotron X-rays allow imaging at micrometer resolution. A 2017 study used synchrotron tomographic microscopy to examine Eocene coprolites, revealing fine internal structures not visible with conventional methods.

Ancient DNA and Biomarker Analysis:

In desiccated (non-mineralized) coprolites, particularly those from archaeological contexts, DNA extraction can identify both the producer and consumed organisms. Parasite eggs within coprolites yield DNA that can be used to reconstruct host–parasite co-evolutionary histories. For deeply mineralized specimens millions of years old, DNA is not preserved, but lipid biomarkers may survive and provide dietary or taxonomic information.

Coprolites occupy a unique niche in paleontology as the most direct source of evidence for ancient dietary behavior, an aspect of biology that skeletal morphology alone can only suggest indirectly.

Dietary Reconstruction: Coprolites provide definitive evidence of what specific animals actually consumed, as opposed to what their dental or skeletal morphology implies they were capable of eating. The T. rex coprolite confirmed bone-crushing feeding behavior; the Maiasaura coprolites revealed unexpected wood consumption.

Paleobotanical Reconstruction: Pollen, spores, phytoliths, and plant fibers in herbivore coprolites enable detailed reconstruction of ancient plant communities, including seasonality information (e.g., identification of plants that bloom only at specific times of year).

Paleoparasitology: Parasite eggs and larvae preserved in coprolites document ancient host–parasite relationships and disease ecology. This subdiscipline has been especially productive in human archaeological contexts but is also applicable to dinosaur and other vertebrate coprolites.

Food Web and Ecosystem Dynamics: By documenting who ate whom, coprolites allow reconstruction of ancient food webs and trophic structures that are invisible in the skeletal record.

Digestive Physiology: The degree of bone fragmentation, the state of plant fiber digestion, and the presence or absence of acid etching on bone surfaces provide inferences about stomach acidity, gut transit time, and overall digestive efficiency.

Coprolites are frequently difficult to distinguish from ordinary rocks, mineral concretions, or other geological features in the field. A cautionary example comes from southwestern Washington state, where nodules collected since the 1920s from a creek bed closely resemble feces and have been used in practical jokes. However, these objects lack calcium phosphate, occur in too many sizes, and are found without associated fossil material. Geologist George Mustoe of Western Washington University has identified them as sinuous-shaped siderite (iron carbonate) deposits formed by an anomalous process without a modern analogue.

Attributing a coprolite to a specific producer is equally challenging. Identification typically relies on a combination of coprolite size, morphology, chemical composition, internal inclusions, and proximity to body fossils. For most specimens, attribution to a specific species remains tentative; only in rare cases where the coprolite was found in direct association with a skeleton—or where only one candidate producer of sufficient size is known from the locality—can a more confident identification be made.