A paper published a few weeks ago on the topic of early animal evolution in the journal Trends in Ecology and Evolution caught my eye. The time period I am referring to is the Early Cambrian, roughly 539 -510 million years ago. A great diversification of animal life occurred during this interval. Many explanations for this phase of rapid animal evolution have been put forth. Expanded shallow marine habitat due to continental rearrangements, an increase in dissolved oxygen, an influx of calcium and zinc to the oceans from continental weathering, both essential for physiologic function and shell building (in case of calcium), and predator prey arms races that drove evolution of novel morphology.
The recent study by Julien Kimming and Russel Bicknell proposes that fecal matter that early animals were expelling also played a role in Cambrian animal radiation. Fecal matter is preserved as lumps of calcium carbonate known as coprolites.
Examples of these Cambrian coprolites are shown in the collage below. They are generally centimeter to millimeter in size.
Source- Russel and Kimmig: Trends in Ecology and Evolution, August 2026.
The fecal lumps also contain crushed shells and disseminated organic matter containing nitrogen and phosphorous. As animals with guts became common, so did fecal pellets. These pellets began sinking into the deeper parts of oceans, bringing nutrients to previously sparsely occupied environments. Habitats increased along with more complex food webs. I’ll be writing more about early animal evolution soon, although focusing on a very different kind of fossil evidence. Stay tuned.
The author's summary of their work has been published in The Conversation.