How ancient poop changed everything
Julien Kimmig’s journey into paleontology took an unexpected turn during his PhD research at a Cambrian excavation site in northern Canada. While sifting through fossils, he noticed something remarkable: approximately half of the specimens he encountered were coprolites—fossilized droppings. The sheer abundance of ancient poop sparked a question that would shape his career: what could explain this peculiar abundance?
Today, as the head of the paleontology and evolution division at the Natural History Museum in Karlsruhe, Germany, Kimmig continues to pursue this unusual line of inquiry. In 2020, when evolutionary biologist Russell Bicknell from Flinders University in Adelaide, Australia, arrived with Cambrian coprolites from southern Australia that had largely been ignored by the scientific community, the two researchers saw an opportunity. They began assembling a comprehensive database of Earth’s earliest fossilized waste products, a project that would eventually reveal a startling pattern in life’s evolutionary history.
The microscopic beginnings
As explained here, the research reveals a dramatic timeline of fecal evolution that mirrors the development of animal digestive systems. In the earliest Cambrian period, approximately 538 million years ago, animal waste was nearly invisible—all droppings existed only at the microscopic scale. As Kimmig explains, this makes sense: before animals developed guts, they couldn’t produce true feces.
“A bowel movement, by definition, is a gut product,” Kimmig clarifies. Simple organisms like jellyfish and sponges may have expelled waste, but without a digestive system processing nutrients, these expelled materials weren’t technically fecal matter. They were simply unused nutrients returned to the water. The difference was fundamental: waste passing through a gut becomes chemically transformed, enriched by the microbes living in the digestive tract, and therefore more valuable as a nutrient source for other organisms.
The earliest actual coprolites—dating to around 523 million years ago and discovered in southwest China—were minuscule formations made of compressed shell fragments. These first true fecal pellets represented a watershed moment: animals now had the physiological machinery to process food internally, and to package their waste in concentrated bundles.
From invisible to visible: The fecal revolution begins
Around 15 million years after those first microscopic coprolites, animal guts underwent dramatic structural changes. Rather than remaining simple straight tubes, digestive systems began to fold and coil. This increased the time food spent being processed, leading to more complex chemical changes and more structured fecal matter.
By 510 million years ago—roughly a quarter billion years before the dinosaurs—the fossil record captures a explosion of fecal diversity. At sites like Chengjiang in China, Sirius Passet in Greenland, and Emu Bay in Australia, researchers found the first macroscopic coprolites, some measuring several centimeters across. These ancient deposits reveal remarkable variety: spheres, elongated cylinders, ellipses, compact pellets, and what researchers dub “exploded fecal carpets”—deposits of feces that dispersed across the seafloor after landing, suggesting looser, more liquid waste.
This wasn’t merely an accumulation of larger poop. The morphological diversity mirrored the sophistication of the guts that produced it. As Kimmig notes, “The fancier the gut, the fancier and bigger the poop.”
Why this matters: The nutrient stream revolution
For most people, the significance of ancient poop isn’t immediately obvious. But for understanding how modern ecosystems formed, coprolites tell a crucial story about nutrient cycling in the oceans.
Before fecal matter aggregation, nutrients dissolved in seawater were largely inaccessible to marine animals. Phosphorus, iron, carbon, and nitrogen floated in the water column, but most organisms couldn’t readily absorb them. When zooplankton and other animals consumed these nutrients, they concentrated them in their bodies. When they excreted waste, that waste became densely packed with bioavailable nutrients—far more so than the diffuse particles floating freely in the water.
This concentration created a powerful biological cascade. Nutrient-rich fecal pellets were heavier than individual nutrient particles, allowing them to sink rapidly into deeper waters. This vertical transport system brought sustenance to ocean depths where few organisms could otherwise survive, opening vast new habitats. Simultaneously, as these aggregates accumulated on the seafloor, they enriched sediments, encouraging larger organisms to burrow and feed. Those burrowing activities churned sediments, introducing oxygen and creating even more diverse habitats—what scientists call bioturbation.
The mechanism was almost self-reinforcing: bigger animals produced more substantial fecal matter, which transported nutrients more efficiently to new depths, allowing animals to expand into previously uninhabitable regions, which led to greater animal size and complexity, producing even more substantial waste. This positive feedback loop fundamentally transformed the planet’s biosphere.
The Cambrian fecal revolution
Kimmig and Bicknell’s recent paper in Trends in Ecology & Evolution argues that this fecal evolution wasn’t merely correlated with the diversification of animal life—it was essential to it. In the Ediacaran period before the Cambrian, life existed, but it looked nothing like the oceans we know. Simple, flat organisms dominated. Once sophisticated guts and diversified fecal matter emerged, the fossil record transforms. Complex three-dimensional animals flourished. The evolutionary radiation that defined the Cambrian explosion coincides precisely with the evolution of coprolites.
“You can’t always say it’s 100 percent the case, but in this instance, we can say 99 percent that fecal matter had something to do with it,” Kimmig emphasizes. Oxygen levels and primary algal productivity certainly played significant roles, but the nutrient delivery system created by fecal matter cannot be overlooked. Especially for colonizing the seafloor and deep ocean regions, fecal matter became the currency of survival.
A question of scientific neglect
One puzzle remains: why has coprolite research been so thoroughly ignored by the broader scientific community? Kimmig offers a candid answer: disgust.
“It’s 100 percent the case,” he says bluntly. Fecal matter is considered disgusting, and in scientific terms, unglamorous—unlikely to yield “high-impact” discoveries that attract funding or professional prestige. As a result, the vast majority of coprolites discovered in the field are never formally documented or added to museum collections. They’re simply left behind, deemed unworthy of scientific attention.
This represents a massive blind spot in our understanding of evolution. A fundamental process shaping the history of life has been systematically ignored not for scientific reasons, but for squeamishness.
Remarkable fossil formations
Among the coprolites Kimmig has encountered, certain formations stand out. One particularly intriguing pattern involves large circular arrangements of fecal matter with an animal carcass in the center. Found at multiple Cambrian sites including Chengjiang, Canada’s Rockslide Formation, and Utah’s Spence Shale, these formations suggest that ocean currents concentrated fecal material and shell debris around dead animals, creating halos of decay that reveal ancient ecological processes.
“We’re still not 100 percent sure how they form,” Kimmig admits. The mixture of fecal matter and fragmented shells—pieces of trilobites and other hard-bodied organisms—indicates significant bottom currents must have been at work, but the precise mechanisms remain mysterious.
The broader implications
The significance of this research extends far beyond academic curiosity. Understanding coprolites illuminates how nutrients cycle through ecosystems, how organisms expand into new habitats, and how evolutionary innovation emerges from unseen biological processes. It demonstrates that evolution isn’t driven only by dramatic adaptations and predator-prey arms races—it’s also shaped by the unglamorous mechanics of digestion and waste.
When Kimmig discusses his research with non-scientists, he encounters predictable skepticism: “Why study feces when there are more important things to investigate?” But once he explains the role coprolites played in enabling animals to diversify, conquer the deep ocean, and establish the foundations of modern ecosystems, people begin to grasp the profound significance.
Final thoughts
The most overlooked insight from Kimmig and Bicknell’s work may be this: sometimes the most fundamental transformations in the history of life emerge not from flashy adaptations, but from quiet biological necessities. Poop wasn’t celebrated by early organisms as an evolutionary advantage. It was simply a byproduct. Yet through the lens of Earth’s fossil record, coprolites reveal themselves to be one of the primary drivers of biological diversification.
That said, Kimmig hasn’t altered his personal relationship with waste. Despite his professional fascination with fossilized feces, his household cat’s litter box receives no special reverence—it’s scooped and discarded like anyone else’s.
Some revolutions, it seems, are best appreciated from an evolutionary distance.