Study reveals the secret weapon that allowed the supremacy of the dinosaurs: they were omnivores

Excrement, vomit and fossilized remains of food in the intestine constitute key clues to understand the spectacular rise of the dinosaurs to supremacy in the animal kingdom, more than 200 million years ago, according to a study published this Wednesday.

Much is known about the existence and extinction of dinosaurs 66 million years ago, but “we know very little about their rise,” a true world conquest that occurred in about thirty million yearssays paleontologist Martin Qvarnström, from Uppsala University in Sweden, and lead author of the study published in Nature.

The team of researchers, led by paleontologist Grzegorz Niedzwiedzki, also from Uppsala, exhaustively reviewed more than 500 bromalites, that is, the fossilized remains of what the dinosaurs in that area digested, vomited and excreted.

By identifying the content of these bromalites and linking it to their producers, researchers “can begin to connect who ate who or what,” Qvarnström explains. This allows us to show “how the ecological role of dinosaurs changed over time.”

The coprolites, that is, fossilized excrement, were analyzed with advanced techniques such as synchrotron microtomography, which revealed almost intact beetles, fish vertebrae or teeth, plant fragments and crushed bones.

Crossing this data with that of paleontology and the evolution of climate and flora, researchers have created a model that explains the progressive domination of the dinosaurs.

“Precursors”

The analysis shows how the average diameter and length of vertebrate bromalites in the region of present-day Poland tripled over a period of 30 million years. During this period, spanning from the late Triassic to the early Jurassic, the size of the owners of these bromalites also grew.

The “precursors” of the dinosaur line, the silesaurus, were “quite small”, barely one meter tall at the neck and weighing a maximum of 15 kilos.

However, while the dominant animals of the time, the dicynodonts, quadrupeds that weighed several tons, fed exclusively on conifers, Silesaurus had a great advantage: they were omnivores.

“Studying their feces, we see that they ate all kinds of things: many insects, fish and plants,” says Qvarnström.

Thanks to this varied diet, these animals were able to quickly adapt to radical environmental changes, such as the Carnian pluvial episode.

This event, which brought humidity, caused a great diversification of the flora, which was difficult for the large herbivores of the time, unable to adjust to the new food resources.

The silesaurus and, later, the long-necked herbivorous dinosaurs—ancestors of the diplodocus—took advantage of these new plants, growing in size and in turn stimulating the development of theropods, bipedal and carnivorous dinosaurs.

At the beginning of the Jurassic, the landscape was dominated by large herbivores and imposing carnivores.

“A little luck”

“The dinosaurs were a little lucky, but they were also very well adapted to this changing environment,” summarizes Qvarnström, whose research avoids taking sides in the debate about the reasons for the supremacy of the dinosaurs.

On the one hand, there are those who advocate “competitive exclusion,” which implies that dinosaurs had anatomical and physiological advantages.

On the other hand, there are the defenders of “opportunistic replacement,” who believe that dinosaurs took advantage of the disappearance of other groups, explains paleontology professor Lawrence H. Tanner, from Le Moyne University, in a complementary article to the study.

The Uppsala team suggests that a combination of both hypotheses allowed the reign of the dinosaurs, with environmental changes coinciding with dietary adaptation.

This research should be considered a “starting point for future studies,” according to Tanner.

Although it employs a “particularly creative methodology” and uses a remarkable range of advanced techniques, its scope is limited to the Polish Basin, which was then part of the supercontinent Pangea.

Qvarnström is aware of these limitations and hopes that the “model built in one region may be valid for others,” especially in southern Pangea, where the first true dinosaurs appeared.