Fossilised droppings tell the story of dinosaurs’ rise to power

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Fossilised droppings tell the story of dinosaurs’ rise to power

Sauropodomorph dinosaurs feeding on newly evolved plants in a wet early Jurassic environment

Marcin Ambrozik

The contents of 200-million-year-old ******* and ****** are helping show how dinosaurs took over the world at the start of the Jurassic *******.

Well-preserved plants, bones, fish parts and even whole insects embedded in widely varying shapes and sizes of ancient animal droppings suggest that dinosaurs’ broad diets made them survivors in a changing ecosystem, compared with other groups of animals. That then led them to grow larger and ultimately establish their “dynasty on land”, says

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at the University of Uppsala, Sweden.

Fossil evidence shows that the first dinosaurs – marked notably by hip joints that position the legs under the body like mammals, rather than sprawled out to the sides like lizards – appeared

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. For tens of millions of years, these early dinosaurs blended into a landscape filled with many other kinds of reptiles. By about 200 million years ago, however, dinosaurs had essentially taken over the planet, while most other reptiles disappeared during the end-Triassic extinction.

What led to the dinosaurs’ domination has remained somewhat mysterious. Qvarnström and his colleagues suspected they might find significant clues hidden in bromalites – fossilised stool and ****** – from dinosaurs and other animals. So they gathered 532 bromalites stored in the

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, which prior research groups had collected between 1996 and 2017 from eight archaeological sites in Poland.

The team estimated the age of each bromalite based on the layer of sediment where it was found and then used its size – ranging from a few millimetres to “pretty substantial faecal masses” – and shape to match it to the animal that probably produced it. They then 3D scanned the fossils to explore their contents. “We realised that they’re packed with food ********,” says Qvarnström.

Coprolites, or fossilised dung, of herbivorous dinosaurs containing plant ********

Grzegorz Niedzwiedzki

Combined with known fossil records and past climate information, the researchers determined that the rise of dinosaurs occurred in several distinct steps. First, omnivorous ancestors of early dinosaurs started outnumbering the non-dinosaurs. Then, they evolved into the first meat-eating and plant-eating dinosaurs.

At that point, an increase in volcanic eruptions and shifts in tectonic plates led to flooding and the development of waterways. The resulting humidity and related changes in the climate seem to have triggered a greater range of plants, leading to the evolution of ******* and more diverse herbivore dinosaurs. Meanwhile, non-dinosaurs – like the 1-tonne dicynodont Lisowicia, whose ******* contained mainly conifer ******** – were less able to adapt to the changing variety of plants.

As the herbivore dinosaurs grew *******, so did their predators. When large carnivorous dinosaurs started to appear by the beginning of the Jurassic ******* – about 30 million years after the first dinosaurs emerged – the transition to a dinosaur-dominated world was complete, Qvarnström says.

“The study shows how climate mainly affected the dominant plants, which in turn gave opportunities for new herbivores at certain points,” says

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at the University of Bristol, ***, who was not involved in the study.

Although it’s hard to be sure that the researchers matched the droppings to the right producer, the findings nonetheless support earlier work from South America suggesting that dinosaur species were already significantly expanding prior to major climate change, he says. “But it took the end-Triassic mass extinction to put in place the final steps of the takeover.”

For

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at the Friedrich-Alexander University in Germany, the study helps answer long-standing questions about the rise of dinosaurs. “It’s not every day that you see fossil ***** in such a high impact journal,” says Dunne, who did not participate in the research. “It’s obviously funny, but it’s also really useful for understanding prehistoric environments. So if you think of early dinosaur evolution as kind of a jigsaw puzzle with missing pieces, it’s just thrown a huge chunk of new pieces in there.”

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