How the 'fecal revolution' changed Earth's ecosystems

An international study led by Flinders University has found a fertile area of inspiration to explain an important step in evolution—and it's a whole lot of poop. The new study describes the "fecal revolution" to explain a crucial turning point in animal and environmental evolution on Earth.

In a new article in Trends in Ecology & Evolution, fossil and evolutionary experts credit the buildup of excrement as a key cause of the "Cambrian Explosion" about 540 million years ago, a brief period when the first marine ecosystems developed and most major animal groups started to appear.

Scientists from Australia and Germany describe how these fossilized pellets, or "coprolites," deposited by primitive sea creatures in the early Cambrian played a vital part in evolution, encouraging marine life to evolve and diversify.

The new research gives an alternative view of this remarkable diversification.

"Next to rising oxygen levels and other contributing factors, the importance of feces in ancient ecosystems is often overlooked," says Dr. Russell Bicknell, an Australian Research Council Early Career Researcher Award (DECRA) fellow at Flinders University's College of Science and Engineering.

Coprolites trace a changing ocean

"We have considered these ancient diets, increasingly sophisticated digestive systems and trophic interactions as part of a much bigger picture to help explain how more organic matter and nutrients poured into the ancient oceans to accelerate ecosystem development at the end of the Ediacaran and early Cambrian periods."

After the earliest animals appeared around 600 million years ago during the Ediacaran Period, more complex digestive systems and the first fossilized coprolites started to appear at the onset of the Cambrian Period.

Bicknell, with lead author Dr. Julien Kimmig from Germany's Karlsruhe Institute of Technology (KIT), says the complexity, shapes and sizes of coprolites and fossil gut systems increased as the Cambrian progressed—with evidence from more than 35 deposits around the globe.

Feeding strategies left a fossil signal

"The fecal matter includes microscopic pellets to centimeter-scale coprolites containing shells and other animal fragments," says Bicknell, an evolutionary biologist and paleobiologist who specializes in arthropods.

"With this shift, we see increasingly complex digestive systems, particularly in early arthropods, which evolve specialized foreguts and digestive glands capable of processing a wider variety of food.

"It becomes clear in the fossil record that the evolution of feeding strategies aligns with the production and distribution of organic carbon and nutrients to start creating conditions we see in modern oceans and later on land, where fertilizer today is used to produce our food," Bicknell adds.