Paleontologists have long puzzled over how the dinosaurs—originally relatively small and of minor importance to the broader ecosystem—evolved to become the dominant species some 30 million years later. Fossilized feces and vomit from dinosaurs might hold important clues to how and why this evolutionary milestone came about, according to a new paper published in the journal Nature.
Co-author Martin Qvarnström, an evolutionary biologist with Uppsala University in Sweden, and his collaborators studied trace fossils known as bromalites, a designation that includes coprolites as well as vomit or other fossilized matter from an organism’s digestive tract. As previously reported, coprolites aren’t quite the same as paleofeces, which retain a lot of organic components that can be reconstituted and analyzed for chemical properties. Coprolites are fossils, so most organic components have been replaced by mineral deposits like silicate and calcium carbonates.
For archaeologists keen on learning more about the health and diet of past populations—as well as how certain parasites evolved in the evolutionary history of the microbiome—coprolites and paleofeces can be a veritable goldmine of information. For instance, in 2021 we reported on an analysis of preserved paleo-poop revealing that ancient Iron Age miners in what is now Austria were fond of beer and blue cheese.
If a coprolite contains bone fragments, chances are the animal who excreted it was a carnivore, and tooth marks on those fragments can tell us something about how the animal may have eaten its prey. The size and shape of coprolites can also yield useful insights. If a coprolite is spiral-shaped, for instance, it might have been excreted by an ancient shark, since some modern fish (like sharks) have spiral-shaped intestines.
A tale of two models
Excavations in the Late Triassic locality at Lisowice, Poland. The site yielded a large number of coprolites of predators and herbivores.
Credit:
Krystian Balanda
Qvarnström et al. were keen to test two competing hypotheses about the dinosaurs’ rise to dominance from the Late Triassic Period (237 million to 201 million years ago) to the onset of the Jurassic Period between 201 million to 145 million years ago. “No single hypothesis seems capable of explaining the rise of dinosaurs fully and critical questions about how dinosaurs established their dynasty on land remain largely unanswered,” the authors wrote about their research objectives.
One hypothesis cites evolutionary competition—the traditional “competitive replacement” model—as a driving factor, in which dinosaurs were better equipped to survive thanks to superior physiologies, anatomical adaptations, and feeding habits. Alternatively the “opportunistic replacement” model suggests that the dinosaurs were better able to adapt to a rapidly changing environment brought about by random processes—volcanic eruptions, climate change, or other catastrophic events that led to the decline and/or extinction of other species.