Fossil dung reveals clues to the rise of dinosaurs

An international collaboration has been able to identify undigested food remains, plants and prey in the fossilised faeces of dinosaurs, which helped reconstruct the rise of the dinosaurs to become the dominant players in Earth’s ancient ecosystems. The study has been published in the journal Nature.

The analyses of hundreds of samples provide clues about the role dinosaurs played in the ecosystem around 200 million years ago. Fossil records show that dinosaurs evolved during the middle part of the Triassic period (247 to 237 million years ago). However, the domination of dinosaurs in terrestrial ecosystems was not seen until approximately 30 million years later, early in the Jurassic period. Many non-dinosaur tetrapods (four-limbed vertebrates) were displaced during this time, but what caused dinosaurs to dominate the ecosystem has remained in question.

The researchers have investigated this transition by reconstructing food webs using over 500 fossilised remains of digestive material (such as faeces or vomit), known as bromalites, from the Polish Basin, which span the Late Triassic to earliest Jurassic. Analyses of these remains (including 3D imaging of their internal structures to reveal undigested food contents) were compared to the existing fossil record, along with climate and plant data, to estimate the changes in size and abundance of vertebrates during this period.

These data indicate that non-dinosaur tetrapods were displaced by the omnivorous ancestors of early dinosaurs, who evolved to become the first carnivorous and herbivorous dinosaurs towards the end of the Triassic era. At this point, the authors suggest that environmental changes resulted in substantial vegetation changes that paved the way for an expansion of herbivore ecospace and the replacement of herbivores by larger and more diverse herbivore species ingested food of a broader range, even including burnt plants. This, in turn, led to the evolution of larger carnivorous dinosaurs by the beginning of the Jurassic period, and completed the transition to dinosaur domination within the ecosystem.

The analysis sheds light on the emergence of dinosaur dominance within the ecosystem of the Polish Basin. “We suggest that the processes shown by the Polish data may explain global patterns, shedding new light on the environmentally governed emergence of dinosaur dominance and gigantism that endured until the end-Cretaceous mass extinction,” they write. Further research using this method could help to clarify this evolutionary history in other parts of the world.