Feces, vomit, and fossilized food remnants from inside the stomachs of ancient animals are often overlooked as mundane byproducts of life, yet they can hold vital clues to our understanding of ancient ecosystems. These seemingly unremarkable substances have now provided fresh insights into one of the most pivotal events in Earth’s history—the rise of the dinosaurs. In a new study published in Nature, a European team of researchers delves into more than 500 fossilized remains known as bromalites—fossilized feces, vomit, and undigested food found within the digestive systems of ancient organisms. This research, led by Martin Qvarnstrom from Uppsala University in Sweden, takes a novel approach to unravel the mystery of how dinosaurs came to dominate the planet, a process that began at least 230 million years ago and culminated in the rise of iconic creatures like the Tyrannosaurus rex.
For a long time, the rise of dinosaurs remained shrouded in mystery. While scientists have learned a great deal about their eventual extinction around 66 million years ago, the reasons for their initial ascendancy have long been the subject of debate. Dinosaurs first appeared during the Triassic period, but it wasn’t until the beginning of the Jurassic Period, some 30 million years later, that they became Earth’s dominant animals. Understanding what caused this shift, and why it took so long for dinosaurs to take their place at the top of the food chain, has long puzzled paleontologists. To explore this critical period of prehistory, Qvarnstrom and his team turned to bromalites from sites in Poland, where they meticulously examined fossilized waste materials to piece together how early dinosaurs made their rise.
By examining the contents of these ancient remains, the researchers gained a window into the diets and behaviors of early dinosaurs and their competitors. The team employed advanced technologies, such as synchrotron microtomography, to create 3D images of the samples. These cutting-edge techniques allowed them to identify the various components found in the fossilized excrement, including insects, plants, fish, and the remains of larger animals. The contents of these bromalites were crucial in constructing a model that illustrated the gradual rise of dinosaurs over millions of years.
Bromalites offer a unique perspective into the ecological dynamics of ancient ecosystems. They provide a direct link between the animals that produced them and the animals that were consumed, revealing insights into the diets, predation, and competition between species. The findings of the study support the idea that early dinosaurs began to rise to prominence due to their ability to adapt to a changing environment. The analysis of these fossilized remains demonstrated that the animals producing them were gradually growing larger over time, with the size of the droppings tripling in both length and width during the 30 million-year period under study. This increase in size reflects the evolutionary success of the species producing the remains.
One of the key animals identified in the study was the Silesaurus, an early ancestor of dinosaurs that lived during the late Triassic period. Unlike the larger, more heavily built herbivorous reptiles of the time, the Silesaurus was relatively small, weighing only around 15 kilograms. These creatures were omnivores, and their diet included a wide variety of foods, from insects and fish to plants. This dietary flexibility likely gave the Silesaurus an advantage over other animals, particularly the larger Dicynodonts, which were dominant at the time but primarily herbivorous and less adaptable to sudden environmental changes.
The study highlighted how the Silesaurus was able to thrive during the Carnian Pluvial Episode, a period of intense rainfall and climate shifts that led to an explosion of plant life. The larger, herbivorous Dicynodonts struggled to adapt to this new plant-based diet, while the Silesaurus and other early dinosaurs were able to take full advantage of the available food sources. As a result, the Silesaurus and its descendants began to grow larger over time, eventually giving rise to the long-necked herbivorous dinosaurs, such as the Diplodocus, that would dominate the Jurassic period.
As these smaller dinosaurs evolved and grew, they provided a food source for the larger carnivorous dinosaurs that would emerge, including the fearsome predators of the Jurassic and Cretaceous periods. This cycle of evolutionary growth and competition helped set the stage for the eventual dominance of dinosaurs across the planet. The study suggests that the rise of the dinosaurs was not the result of any single factor but rather a combination of evolutionary advantages and environmental changes that allowed certain species to outcompete others and thrive in new and changing ecosystems.
While the study provides important insights into the early stages of dinosaur evolution, it does not settle the longstanding debate about the causes of their rise to dominance. Two competing theories have emerged to explain the phenomenon. One theory posits that early dinosaurs gained an advantage through key physiological traits, such as an upright posture, which allowed them to move more efficiently and outcompete other animals. The other theory suggests that environmental upheaval, such as volcanic eruptions or shifts in climate, played a more significant role by eliminating many of the animals that previously held ecological dominance and creating opportunities for the dinosaurs to rise.
The researchers behind the bromalite study propose that both factors likely contributed to the rise of the dinosaurs. The physiological advantages of early dinosaurs, such as their bipedal stance and rapid metabolism, may have allowed them to capitalize on environmental changes that wiped out other species. This combination of evolutionary innovation and environmental opportunity may have been the key to their eventual dominance.
Despite the compelling evidence provided by the study, it remains just the beginning of a deeper exploration into the factors that drove the rise of dinosaurs. As Lawrence Tanner, a researcher at Le Moyne College in New York, points out in a commentary accompanying the study, the research methodology is creative and innovative but limited in its scope. The study focuses on a specific region, the Polish Basin, which was part of the northern portion of the Pangea supercontinent during the Triassic period. Tanner suggests that future studies should apply this model to other regions of the world, such as the southern part of Pangea, where the first dinosaurs appeared, to further refine our understanding of their evolutionary history.
Qvarnstrom himself also sees the potential for expanding the research. He envisions applying the models developed in this study to other regions and time periods to gain a more comprehensive understanding of how dinosaurs rose to power. The study provides a valuable framework for future research into the diets, behaviors, and environmental interactions of early dinosaurs, as well as the ecological dynamics that shaped their evolution.
Reference: Martin Qvarnström et al, Digestive contents and food webs record the advent of dinosaur supremacy, Nature (2024). DOI: 10.1038/s41586-024-08265-4