Scientists have uncovered a significant but previously underappreciated factor behind the Cambrian explosion—a period around 540 million years ago when animal life rapidly diversified and complex ecosystems emerged. This factor, described as a “faecal revolution,” involved a substantial increase in the amount of excrement deposited into ancient oceans by early animals, according to new research.
The study, published in *Trends in Ecology & Evolution*, highlights fossilized excrement, or coprolites, as a key piece of evidence in understanding how early animal life transformed during this critical period. While the rise in oxygen levels in the seas has long been considered a primary driver behind the Cambrian explosion, the researchers argue that the role of increased biological waste in shaping ecosystems has been largely overlooked.
Animals first appeared roughly 600 million years ago in the Ediacaran period, but there is limited evidence that they had fully developed digestive systems capable of producing fossilizable waste during this time. In contrast, the Cambrian period shows the emergence and proliferation of coprolites, which grew in size and diversity alongside the development of more complex digestive anatomy.
The research team examined 36 fossil sites worldwide, including locations in Australia, China, and North America. Their findings reveal a progression from microscopic faecal pellets to larger, more varied coprolites, which correspond with the advent of more efficient digestion in animals. This increase in biological waste is believed to have transported organic matter and nutrients into deeper ocean layers that were previously nutrient-poor, fostering conditions conducive to the growth of larger and more complex marine organisms.
This process created a feedback loop: more complex animals produced greater quantities of waste, which in turn enriched marine environments and supported further biological complexity and more intricate food webs, including predators and scavengers.
Dr. Russell Bicknell, an evolutionary biologist at Flinders University in Adelaide, emphasized the significance of this discovery, noting that faecal matter played a crucial yet underrecognized role alongside rising oxygen levels and other factors in shaping ancient ecosystems.
The impact of this “explosion of excrement” is not just a phenomenon of the distant past. Modern ocean systems continue to rely on faecal pellets as a mechanism for transporting organic carbon and nutrients from sunlit surface waters to deeper sea layers, underscoring the enduring ecological importance of biological waste throughout Earth’s history.