A diet of beetles and burnt plants
In a clay pit near the village of Krasiejów, Poland, paleontologists unearthed evidence detailing life during the Late Triassic, around 230 million years ago. This evidence was bones and hundreds of coprolites (fossilized feces) and bromalites (fossil vomit). These trace fossils provide a direct record of the diets and interactions within an ancient ecosystem on the supercontinent Pangaea. The site has yielded remains of various animals, including a large predatory rauisuchian called Polonosuchus silesiacus and early dinosauromorphs—the ancestors of dinosaurs.
An important animal in this environment was Silesaurus opolensis, a dinosauromorph about 2.3 meters long. Traditionally considered an herbivore based on its teeth, analysis of its likely coprolites revealed a more complex diet. Researchers took the fossilized feces to the European Synchrotron Radiation Facility (ESRF) in France. There, they used a technique called propagation phase-contrast synchrotron microtomography, hitting the coprolites with high-energy X-rays to create detailed 3D models of their contents without destroying them. The scans revealed numerous beetle remains, including delicate wing cases (elytra) and leg parts, suggesting Silesaurus opolensis was omnivorous, deliberately targeting insects. This pecking behavior is analogous to some modern birds.
Surviving the Carnian Pluvial Episode
The dietary flexibility of animals like Silesaurus was an advantage during a period of intense climate change known as the Carnian Pluvial Episode, which lasted from roughly 234 to 232 million years ago. This event, driven by massive volcanic activity, caused a shift from arid conditions to a much hotter, more humid climate with increased rainfall. This climatic upheaval triggered a major floral change, causing the extinction of previously dominant herbivores like dicynodonts and rhynchosaurs, who were specialist eaters.
The coprolite analysis shows that dinosauromorphs were generalists. They consumed a wide variety of foods, including ferns, cycads, insects, and even charred plant material from frequent wildfires. This ability to exploit different food sources, especially those available after environmental disturbances like fires, allowed them to survive and thrive while their competitors faltered. The food web reconstruction, based on over 500 bromalites collected over 25 years, demonstrates how this dietary adaptability was a foundation for the subsequent 30-million-year rise of dinosaurs to global dominance. Other coprolites from the site revealed different parts of the food web; some contained crushed bivalve shells and the remains of fish, likely from a lungfish.