After their very first appearance, it took the dinosaurs 30 million years to become the dominant group of animals on the planet. But how did they achieve this “seizure of power”? Paleontologists have analyzed food webs during this rise period and found that dinosaurs became more relevant at several stages and also received help from environmental changes, the team reports in Nature.
At the time of their first appearance 230 million years ago, the dinosaurs still lived in the shadow of other large reptiles. It wasn’t until 30 million years later that they finally came to dominate ecosystems worldwide. But how did they achieve this rise? Some paleontologists assume that the dinosaurs were superior to their contemporaries due to various adaptations and therefore displaced them. Others suspect that significant environmental changes wiped out the previous rulers of the animal world, making way for the dinosaurs. But who is right?
An archive of feces
In order to find out more about the rise of the dinosaurs, researchers led by Martin Qvarnström from Uppsala University have now consulted a rather unconventional contemporary witness: fossilized feces. Using synchrotron microtomography, the team looked into over 500 fossil remains of digestive material from a fossil-rich region in southern Poland and were able to reconstruct the food webs that existed there between 230 and 200 million years ago. “Putting together who ate who in the past is real detective work,” says Qvarnström. But: “If we can examine what the animals ate and how they interacted with their environment, we can better understand why the dinosaurs were so successful.”
Inside the fossilized excrement, Qvarnström and his colleagues found undigested remains of fish, insects, bones, teeth and a variety of plant remains. By combining this dietary information with other clues such as fossil footprints and skeletal finds, the team was able to reconstruct how the ecosystem and the role of dinosaurs within it changed over time.
A diverse plant diet paved the way
Specifically, it was shown that the dinosaurs’ “takeover of power” must have taken place in five phases. At the beginning, small, omnivorous dinosaur precursors lived in the shadow of the other reptiles of their time, and in phase two the first predatory dinosaurs appeared. In phase three, these diversified and produced large species for the first time. At the same time, the first herbivorous dinosaurs also developed. In phases four and five, the diversity and size of the dinosaurs increased even further and their dominance in the ecosystem was finally established, as Qvarnström and his team explain.
However, in order for the last two phases to take place, external help was apparently needed in the form of drastic environmental changes. As the researchers report, volcanic activity probably caused the plant world to change significantly. This was to the disadvantage of the previously predominant herbivorous reptiles, as some of them had specialized heavily on certain plant species. The herbivorous dinosaurs, on the other hand, were significantly less picky and over time took over the ecological niches of the previous leadership team. “To avoid extinction, you have to eat a lot of plants, and that’s exactly what the early herbivorous dinosaurs did. The reason for their evolutionary success is a true preference for green and fresh plant sprouts,” explains co-author Grzegorz Niedźwiedzki.
Source: Uppsala University; Specialist article: Nature, doi: 10.1038/s41586-024-08265-4