It was not always easy being a dinosaur. When they scampered onto the scene 230 million years ago, these “terrible lizards” were prehistoric pipsqueaks among a slew of bigger, badder reptiles brimming with teeth and bolstered with armor. But 30 million years later, many of these older reptiles were gone, and dinosaurs reigned supreme.
Determining how dinosaurs achieved worldwide domination has been difficult because of a scarcity of well-preserved early dinosaur skeletons. So a team of researchers recently explored another aspect of the fossil record: fossilized feces and vomit, known as bromalites. In a paper published Wednesday in the journal Nature, the scientists used these materials to recreate how early dinosaurs fit into food webs across 30 million years in a prehistoric region that is today part of Poland.
The most famous bromalites are fossilized feces, also known as coprolites. But bromalites also preserve digestive byproducts like regurgitations and gut contents that help researchers pinpoint who was eating whom in ancient ecosystems.
Bromalites may often become the butt of jokes, said Stephen Brusatte, a paleontologist who was not involved in the study and who noted that “academic paleontologists can be prone to toilet humor, too.” But they preserve crucial clues about the ecology of the earliest dinosaurs.
“This is exactly what we need to understand the predator and prey links from millions of years ago,” he said.
Most research on the Triassic Period, when dinosaurs were cat-size, has centered on fossilized bones. Martin Qvarnström, a paleontologist at Uppsala University in Sweden and his colleagues focused instead on bromalite specimens from the Polish Basin, a geological formation in central Poland that spans the Late Triassic into the Jurassic. Here, paleontologists have uncovered fossilized bones, footprints and a payload of petrified poop and puke from a variety of creatures including sharks, giant amphibians and dinosaurs.
The new study examined more than 500 bromalite specimens that collectively weighed more than 220 pounds. The samples came from five intervals in the rock record. Some of the bromalites were sliced into thin cross sections or micro-CT scanned.
These methods provided detailed glimpses of paleo-diets. Some bromalites contained leaves and well-preserved insects that retained antennae. Others had fish scales, bone and even fragments of chipped teeth.
Several bromalites revealed that the earliest dinosaurs were opportunistic omnivores that ate mainly insects. Slightly more recent dinosaur dung belonged to early carnivores and small herbivores. Even younger bromalites were linked to the emergence of the first large herbivorous dinosaurs, sauropodomorphs. The early Jurassic deposits yielded the bromalites of large predatory dinosaurs that had evolved to hunt large herbivores.
“The results of the research show that dinosaurs slowly took control of the world,” said Grzegorz Niedzwiedzki, one of Dr. Qvarnström’s coauthors who is also a paleontologist at Uppsala University. “At the very end of the Triassic, something happened that opened the door wide for them to enter the Jurassic period.”
To understand that something, the team compared the trends they observed in the bromalite specimens with skeletal fossils and paleoclimate data. They found that shifting tectonics and volcanic activity changed the local climate in the Polish Basin and diversified local plant life. This buffet of greens was a boon to herbivorous dinosaurs, whose droppings contain a more diverse assemblage of plants than more specialized herbivores like dicynodonts, beefy mammal ancestors that could grow larger than rhinos.
“The ability to digest and eat the newly introduced plants probably gave dinosaur herbivores a greater advantage over pre-existing plant eaters,” Dr. Qvarnström said. This trend is reflected in the Polish Basin fossil record, with dicynodonts disappearing by the Jurassic as early sauropods and other plant-eating dinosaurs proliferated.
While the current paper focuses exclusively on the Polish Basin, the researchers believe that other regions experienced a similar ecological shift.
“There are probably Triassic and Jurassic coprolites in many places,” Dr. Niedzwiedzki said. “I think more and more researchers will keep an eye on them.”
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