Fossilized feces and vomit contain clues to the rise of the dinosaurs

Dinosaurs emerged around 230 million years ago during the Triassic. But how they came to dominate during the Jurassic isn’t clear. Now researchers have dug up new hints—from fossilized feces, gut parts, and vomit—that early dinos’ ability to adapt to changing environmental conditions contributed to their rise over 30 million years (Nature 2024, DOI: 10.1038/s41586-024-08265-4).

There’s a lot to learn from fossils that aren’t as massive as dinosaur skeletons, says Martin Qvarnström, a vertebrate paleontologist at Uppsala University. “Seemingly unremarkable fossils could tell remarkable stories and contain remarkable pieces of evidence of past life.”

Qvarnström, paleontologist Grzegorz Niedźwiedzki of Uppsala University, and their colleagues have examined the contents of more than 500 bromalites, or fossilized digestive remains, from the Polish Basin, a sedimentary rock deposit that contains fossils from the Jurassic-Triassic transition, to reconstruct ancient food webs.

Fossilized droppings, or coprolites, vary greatly, Qvarnström says, from small and sausage shaped, to spirals, to enormous mounds left by big dinosaurs. They can contain materials such as bones, teeth, and plant fragments. Vomit is harder to recognize; it often looks like a pile of chewed-up bones. “One of the things that’s really great about bromalites is they are made out of material that itself is very good at preserving other fossil remains,” says Paul E. Olsen, a vertebrate paleontologist at Columbia University’s Lamont-Doherty Earth Observatory who wasn’t part of the study.

The researchers identified probable source organisms for the remains found at the study sites, based on the bromalites’ size, shape, and contents. At a synchrotron X-ray source, the team took computed tomography (CT) scans of over 100 of these fossils. They digested some fossils with acid to liberate plant matter for study under the microscope.

The researchers also examined a handful of bromalites for traces of biomolecules. In some, they found biomarkers related to food consumption. These included phytanic and pristanic acids, which are found in fish oil and point to how common piscivory was at some Polish Basin sites. Some coprolites contained organics that came from consumed prey, Qvarnström says, “which is amazing and something we have to explore further.”

Along with the bromalites, the researchers also considered body fossils, animal tracks, and what’s known about climate and environmental changes during this time. The team concluded that the first dinosaurs from these Polish Basin sites were opportunistic eaters that chowed down on insects, fish, and plants. The animals later diversified as big, predatory dinosaurs emerged along with the first herbivorous dinosaurs, who adapted to exploit a greater variety of plants. The presence of charcoal in some bromalites from early herbivores hints that the animals may have eaten charred wood to detoxify compounds from certain plants.

During this time, the hot climate transitioned from dry to more humid. Dinosaurs were not as specialized as the other animal groups, and they were better at coping with the changing conditions, Qvarnström says. Previous theories have suggested that dinosaurs either outcompeted other creatures or were opportunistic omnivores that flourished when other animals declined. The new study points to a mixture of dinosaur opportunism and competition with other groups.

“The study did a great job of proposing a testable hypothesis for the rise of the dinosaurs,” writes Mary H. Schweitzer, a molecular paleontologist at North Carolina State University who wasn’t part of the work, by email. That said, “it is virtually impossible to definitively identify the producers of such digestive leavings. So, this part of the work is, at some level, speculative,” she says.

There may have been adaptations that were not measured in the bromalites that allowed dinosaurs to thrive during times of global change, Schweitzer says. For instance, it’s possible that dinosaurs and their ancestors may have been better able than other groups to withstand lower oxygen levels during the Triassic because of molecular adaptions, such as a modified hemoglobin, that more efficiently delivered oxygen to tissues.

Studying bromalites at other locations to construct food webs could help unravel evolutionary trends during the Triassic-Jurassic transition. And Qvarnström wants to test whether similar circumstances aided the rise of dinosaurs in other regions.

Bromalites from this period have largely been ignored, Columbia’s Olsen says. But they could help test other hypotheses about animal adaptation. Many of the animals that survived the end-Triassic extinction were able to deal with cold, Olsen says. These creatures—such as feather-insulated dinosaurs and fur-bearing mammals—may have been better suited to handling abrupt cold spells brought on by volcanic activity. “It’s really an important work,” Olsen says, “It documents how you can use these formerly what were thought to be basically trash fossils to recover details of a very important transition in Earth history.”