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The earliest dinosaurs were unremarkable bit players on a supercontinent full of others ancient reptiles when they first evolved about 230 million years ago.
Fast forward 30 million years, however, and dinosaurs dominated the planet, coming in all shapes, sizes, and forms, while many of their reptilian counterparts died out.
Exactly why they were so evolutionarily successful has long been a mystery, but new research suggests that some of the answers to that question may be contained in what they left behind: dinosaur poop.
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“We know a lot about their lives and extinctions, but not how they came to be,” said Martin Qvarnström, lead author study on the rise of the dinosaurs published on Wednesday in the journal Nature and paleontologist at Uppsala University in Sweden.
To better understand the extinct giants, Qvarnström and his colleagues investigated overlooked fossils known as bromalites: remains from the digestive system – known as dinosaur feces and vomit.
They studied more than 500 fossils collected over 25 years from about 10 locations in the Polish Basin, an area in southern Poland.
The remains date from the Late Triassic to Early Jurassic period, from about 247 million years ago to 200 million years ago.
“(Bromalites) contain so much paleoecological information, but I don’t think paleontologists really acknowledge that and they mostly see it as a joke; collect a few coprolites because it’s funny,” Qvarnström said, referring to the fossilized feces.
They found that the fossilized feces and regurgitated contents – scientifically known as coprolites and regurgitalites – increased in size and variety over time, indicating the emergence of larger animals and a different diet.
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By studying the shape and content of the bromalites and correlating them with the fossilized skeletons and footprints found at the sites, the researchers were able to identify and categorize the animals that likely produced them.
This allowed researchers to understand how many and what kinds and sizes of dinosaurs, as well as other vertebrates, were in the landscape at a given time.
The analysis, which took 10 years, allowed the team to piece together why dinosaurs rose to prominence.
Revelations from ancient poop
In some cases, it was possible to make a visual estimate of what type of dinosaur was responsible for the bromalite based on the size and shape of the fossil—the spiral-shaped coprolite probably came from an animal with a spiral gut—but in many other cases, it was necessary to make a detailed 3D scanning the internal structure of bromalites using specialized equipment to understand what the fossils contain.
Ancient digestive remains can “look like something your dog left in the park and it’s very obvious that they are,” he said.
“In other cases, especially herbivores, they are more difficult to identify.”
The team scanned the fossil’s internal structure at the European Synchrotron Radiation Facility in Grenoble, France.
The massive facility, the 844-meter ring-shaped synchrotron, generates beams of X-rays 10 trillion times brighter than medical X-rays and allows scientists to study matter at the molecular and atomic level.
“It’s a bit like a CT scanner in a hospital. It works the same way, but with a lot more energy. We need that to get this really high resolution and good contrast,” said Qvarnström.
Coprolites contained the remains of fish, insects and plants, and sometimes other prey animals.
Some remains were beautifully preserved, including tiny beetles and half-complete fish.
Other coprolites contained bones crushed by predators.
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“The skeletal fossils, footprints and bromalites from the site in Poland provide a series of discrete snapshots in time that show the transition from a world with few dinosaurs to one dominated by dinosaurs,” said Lawrence H Tanner, a paleontologist in the Department of Biological and Environmental Sciences at Le Moyne College in New York.
Tanner was not involved in the study.
“Using the techniques from this study in other locations would provide a more global context and create a nuanced picture,” Tanner wrote in a commentary published with the research.
Reconstructing the rise of the dinosaurs
The authors came up with five stages to explain the dominance of the dinosaurs: their ancestors were omnivores, eating plants and animals.
They evolved into the first carnivorous and herbivorous or herbivorous dinosaurs.
A key turning point occurred when increased volcanic activity may have led to a more diverse range of plants to feed on, followed by the appearance of large and more diverse herbivorous dinosaurs.
On the other hand, this phase led to the evolution of the giant carnivorous dinosaurs beloved by movie directors and childhood books at the beginning of the Jurassic period 200 million years ago.
The supremacy of the dinosaurs lasted until an asteroid that hit the coast of present-day Mexico 66 million years ago condemned the dinosaurs to extinction.
Before this latest research, two theories were proposed to explain the transition from a world dominated by non-dinosaur reptiles to a world where dinosaurs were ascendant, the study said.
According to the study, one model suggested that dinosaurs evolved to physically outperform their rivals.
The upright stance of dinosaurs resulting from the position of their hind limbs just below the body, combined with flexible ankles, made them highly agile and more efficient than their evolutionary competitors such as splayed-legged reptiles.
On the other hand, some researchers believe that the dinosaurs were coincidentally better able to adapt to the dramatic climate changes that occurred at the end of the Triassic.
Qvarnström said research based on field fossils suggested that a combination of the two hypotheses provided a more likely explanation, with a “complex interplay of several processes” that meant dinosaurs were better able to cope as environmental changes altered food availability.
For example, the study found that food remains extracted from bromalites belonging to dicynodonts, an ancient relative of turtle-headed mammals, suggest that the creature had a limited diet, feeding mostly on conifers.
It disappeared from the fossil record approximately 200 million years ago.
Dinosaurs, on the other hand, ate a wide variety of plants.
For example, the team found that the coprolite contents of the first large herbivorous dinosaurs, the sauropodomorphs, contained large amounts of ferns, but also many other types of plants and charcoal.
Grzegorz Niedźwiedzki, senior study author and paleontologist based at the Department of Organismal Biology in Uppsala; of evolution and development, said that the reason for the evolutionary success of dinosaurs was a message that is still valid today: “Eat your vegetables and live longer”.
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