An Explosion of Feces May Have Triggered Earth’s Explosion of Species

A significant shift in Earth's ecosystem during the Cambrian Period, approximately 539 to 486 million years ago, saw the emergence of complex life forms. This event, known as the "Cambrian explosion," saw the arrival of almost all major animal groups, including those with shells, skeletons, and other features that allowed larger organisms to thrive.

While scientists have previously theorized that the increase in atmospheric oxygen levels provided a metabolic boost to facilitate this explosion, a recent review study published in Trends in Ecology & Evolution proposes an alternative explanation: a surge in fecal matter. According to the study led by paleobiologists Julien Kimmig and Russell Bicknell, animal excrement played a crucial role in the nutrient cycle of the ancient ocean, infusing the water column with essential elements such as carbon, nitrogen, phosphorus, and iron.

The earliest evidence of ocean animals dates back to the Ediacaran Period, around 600 million years ago, but fossilized feces, known as "coprolites," have only been discovered in 36 fossil deposits since the Cambrian. These coprolites provide valuable insights into the diets and trophic interactions of Cambrian animals, helping researchers understand the food webs and nutrient cycling that occurred millions of years ago.

The researchers suggest that as more complex digestive systems evolved, a wider variety of food was processed, leading to an increased production of feces. This surge in feces made nutrients more readily available to other organisms, creating the necessary conditions for the development of complex life. The study highlights the often-overlooked importance of feces in ancient ecosystems and emphasizes the need to consider it as a key factor in understanding the acceleration of ecosystem development during the Cambrian Period.