How the dinosaurs ceased to dominate the Earth is well known: an asteroid collided with the planet 66 million years ago, triggering a horrific mass extinction of the species. But how the dinosaurs, from humble, relatively small animals initially, managed to dominate, is not equally well known.

New research based largely on fossilized feces, ememas and gut contents—evidence of who eats what and who gets eaten by whom—sheds light on how dinosaurs broke up competition during the Triassic Period. The study focused on an area in Poland where many fossils from this era have been found.

Dinosaurs appeared about 230 million years ago and were initially overshadowed by other animals, such as their relatives, the giant crocodiles, terrestrial and semi-aquatic as well as various herbivorous creatures, which were elephant-sized or quadrupedal, scaly reptiles. But about 200 million years ago the dinosaurs came to dominate and their main competitors disappeared.

“We approached the rise of the dinosaurs in a completely innovative way. We analyzed their diet to see what role they played in the ecosystem during the first 30 million years of their evolution,” said paleontologist Martin Kvarnström, of Uppsala University, lead author of the study published today in the scientific journal Nature.

The first dinosaurs and their close relatives were opportunists: they ate whatever they could find, such as insects and fish. Then, larger and more “specialized” predators appeared, alongside herbivorous dinosaurs that were apparently better adapted to the new plants that thrived when the climate became wetter.

Fossilized droppings or coprolites, together with emsmata, are called bromalites. By examining the undigested food (plants and prey) in bromalites, scientists can discern the eating habits of different species and describe how an entire ecosystem was fed.

As part of the study, they examined hundreds of bromalites, mainly coprolites. “We studied more than 100 kilograms of fossilized feces,” said Gregors Niedwiedzki, a paleontologist and geologist at Uppsala University and the Geological Institute of Poland.

How can scientists know what species feces or vomit belong to? Fossilized bones and footprints show which animals were present in the area at a particular time. And researchers calculate who left a particular coprolite based on its size and shape, the type of undigested food, and the digestive systems of the living relatives of those extinct species.

The first species of the dinosaur family in this area were omnivores, such as the two-meter Silesaurus. “It was an opportunistic creature that ate insects, fish and plants. Some of the insects were remarkably well preserved,” noted Kvarnström.

The large herbivorous and carnivorous dinosaurs appeared at the end of the Triassic Period, which ended 201 million years ago. Environmental changes, such as increased volcanic activity on Earth, led to the appearance of a greater variety of plants, which were exploited by the large herbivorous dinosaurs. The abundance of large herbivorous dinosaurs also led to the evolution of their larger carnivorous relatives.

The other large carnivores died out before the start of the next period, the Jurassic, and the dinosaurs came to dominate. 200 million years ago, meat-eating dinosaurs 8 meters long and herbivores that were 10 meters in size walked the Earth.

Smoke, a 20-foot-long carnivorous relative of the dinosaurs, lived about 210 million years ago. The coprolites showed that it used its powerful jaws to crush bones and eat the nutritious marrow – a diet similar to that of later dinosaurs, such as Tyrannosaurus rex.

Coprolites of herbivorous dinosaurs hid surprises. “Another interesting and mysterious discovery was that we found biochemical evidence of burnt plants as well as pieces of charcoal. Did the dinosaurs eat the charcoal along with the burnt plants? The ferns, the remains of which we found in the coprolites, are toxic, and the carbon may have neutralized the toxins,” Nijwiendzki said.

“Dinosaurs had luck on their side but they also adapted very well to this changing environment,” Kvarnström summarized.

In an article accompanying the study, paleontology professor Lawrence H. Tanner recalled that scientists still disagree about why dinosaurs came to dominate – some say their anatomical advantages out-competed other species to extinction, others that they benefited from the extinction of other species. The Uppsala team hypothesizes that a combination of the two occurred, with environmental changes coinciding with the adaptation of the dinosaurs’ diet.

This research should be considered a “starting point for future studies,” Tanner noted, because it was limited to the area of ​​Poland, which at the time was part of the Pangea supercontinent. However, Kvarnström hopes that “the model he applied to one zone could also apply to others, especially in southern Pangaea,” an area where the first real dinosaurs appeared.