In the early days of the dinosaurs' existence, around 230 million years ago, they were unremarkable creatures sharing the supercontinent with a myriad of other ancient reptiles. However, a mere 30 million years later, dinosaurs rose to dominance, exhibiting a plethora of forms and sizes while many of their reptilian contemporaries declined. The secret to their evolutionary triumph has long been an enigma, but recent research points to clues hidden within their remains —specifically, dinosaur droppings.

"We know a lot about their lives and extinction but not how they came about," said Martin Qvarnström, lead author of a study published in Nature and a paleontologist at Uppsala University in Sweden. To unravel the mysteries of these ancient behemoths, Qvarnström and his team delved into the understudied fossils known as bromalites—relics from the digestive system, or in layman's terms, dinosaur excrement and vomit.

They examined over 500 fossils collected from approximately 10 sites in the Polish Basin over a 25-year period, dating back to the Late Triassic to early Jurassic Period, roughly 247 million to 200 million years ago.

"Bromalites contain so much paleoecological information, but I don’t think paleontologists have really acknowledged that and have seen them mostly as a joke," Qvarnström remarked, referring to fossilized feces. The team discovered that these fossilized remnants, scientifically termed coprolites and regurgitalites, increased in size and variety over time, signaling the emergence of larger creatures with diverse diets.

By analyzing the shape and contents of the bromalites and correlating them with fossilized skeletons and footprints, the researchers were able to identify the animals likely responsible for them. This process allowed them to deduce the number and types of dinosaurs and other vertebrates present in a given ecosystem at specific times.

The decade-long analysis revealed insights into why dinosaurs rose to prominence. In some instances, the type of dinosaur responsible for a bromalite could be visually inferred from its size and shape—a spiral-shaped coprolite likely originated from an animal with a spiral gut. However, in many cases, detailed 3D scans of the bromalites' internal structures were necessary to understand their contents, using specialized equipment at the European Synchrotron Radiation Facility in Grenoble, France.

This facility, with a circumference of 844 meters (2,800 feet), generates X-ray beams 10 trillion times brighter than medical X-rays, enabling scientists to study matter at the molecular and atomic level.

"The coprolites contained the remains of fish, insects, and plants, and sometimes other prey animals. Some remains were beautifully preserved, including tiny beetles and half-complete fish. Other coprolites contained bones crushed by predators," Qvarnström said. The skeletal fossils, footprints, and bromalites from sites in Poland provided a series of discrete temporal snapshots that demonstrated a transition from a world with few dinosaurs to one in which they dominated, according to Lawrence H. Tanner, a paleontologist at Le Moyne College in New York, who was not involved in the study.

The researchers identified five phases explaining dinosaurs' ascendancy: Their ancestors were omnivorous, consuming both plants and animals. They evolved into the first carnivorous and herbivorous dinosaurs. A pivotal turning point occurred when increased volcanic activity led to a more diverse range of plants, followed by the emergence of large and diverse herbivore dinosaurs. This phase, in turn, led to the evolution of the giant carnivorous dinosaurs at the beginning of the Jurassic Period 200 million years ago. The reign of the dinosaurs persisted until an asteroid impact off the coast of present-day Mexico 66 million years ago led to their extinction.

Before this research, two theories had been proposed to explain the transition from a world dominated by non-dinosaurian reptiles to one in which dinosaurs were ascendant. One model suggested that dinosaurs evolved to physically outcompete their rivals, with their upright stance and flexible ankles making them more agile and efficient than their evolutionary competitors.

Alternatively, some researchers believe dinosaurs were by chance better able to adapt to dramatic climate changes at the end of the Triassic. Qvarnström said the research based on the Polish fossils suggested a combination of the two hypotheses provided a more likely explanation, with a "complex interplay of several processes" that meant dinosaurs were better able to cope with environmental shifts and changes in food availability.

For example, the study found that food residues extracted from bromalites belonging to dicynodonts, an ancient mammal relative with a turtle-shaped head, suggested that creature had a restricted diet, feeding principally on conifers. It disappeared from the fossil record around 200 million years ago. Dinosaurs, on the other hand, appeared to consume a wide array of plants. The team found that the contents of coprolites from the first large herbivorous dinosaurs, the sauropodomorphs, contained large quantities of tree ferns but also many other types of plants and charcoal. The team suspects that charcoal helped detoxify the ferns, which can be toxic.

The study’s senior author, said the reason behind the dinosaurs’ evolutionary success was a message that still applied today: “Eat your veggies and live longer.”