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Dinosaurs' ability to adapt to new diets may explain their success

Dinosaurs dominated the land habitats of Earth for over 100 million years during the Mesozoic era. At the peak of their success, they included species that were herbivorous, like the long-necked sauropods, and others that were dedicated carnivores like Tyrannosaurus rex and its relatives. However, they were not always the grand and impressive reptiles with which we are so familiar.  

When dinosaurs first evolved, way back in the early Triassic Period (some 230 million years ago), they were not initially very successful or diverse. They were mostly small and lived in the shadow of the much more successful crocodile-like archosaurs. Scientists do not know how diverse they were in terms of their diets and ecology, but they do know that something happened during their early evolution in the Triassic, that enabled them to adapt to a wide range of habitats and lifestyles. 

At the end of the Triassic Period, a mass extinction event occurred that wiped out the crocodile-like competitors, but most of the early dinosaurs survived. After this event, the dinosaurs were able to adapt and evolve into a diverse array of species that dominated the earth until their extinction, 66 million years ago. 

Significant ways in which the early dinosaurs changed involved the shapes of their skulls and the morphology of their teeth. This is thought to indicate that they began to diversify their diets and eat different foods. By looking at the tooth shapes of the earliest dinosaurs and simulating their tooth function with computational modelling, a team of researchers has now been able to compare them to living reptiles and their diets. Their findings are published in the journal Science Advances.

“Soon after their origin, dinosaurs start to show an interesting diversity of skull and tooth shapes. For decades, this has made paleontologists suspect that different species were already experimenting with different kinds of diets,” explained study lead author Dr. Antonio Ballell from the University of Bristol.

The researchers compared the fossilized teeth of early dinosaurs to those of modern lizard species and tried to infer what the dinosaurs ate, based on the similarities with modern lizard species, for which the diets are known.  

“We investigated this by applying a set of computational methods to quantify the shape and function of the teeth of early dinosaurs and compare them to living reptiles that have different diets,” said Dr. Ballell. “This included mathematically modeling their tooth shapes and simulating their mechanical responses to biting forces with engineering software.”

“With this battery of methods, we were able to numerically quantify how similar early dinosaurs were to modern animals, providing solid evidence for our inferences of diets. Theropod dinosaurs have pointy, curved and blade-like teeth with tiny serrations, which behaved like those of modern monitor lizards,” explained study co-author Professor Mike Benton. “In contrast, the denticulated teeth of ornithischians and sauropodomorphs are more similar to modern omnivores and herbivores, like iguanas.”

The innovative study used machine learning models to classify the earliest dinosaurs into the different diet categories, based on their tooth shape and mechanics. The researchers found that some of the species, such as Thecodontosaurus (one of the earliest and oldest known dinosaurs), had teeth that were perfectly adapted for a diet of plants. However, many groups that ended up being herbivorous actually had ancestors that were omnivorous. And the long-necked herbivores, such as Diplodocus, had ancestors that ate meat. 

The researchers suggest that this ability to diversify their diets early in their evolution likely explains the evolutionary and ecological success of the dinosaurs.

“Our analyses reveal that ornithischians – the group that includes many plant-eating species like the horned dinosaurs, the armored ankylosaurs and the duck-billed dinosaurs – started off as omnivores. And another interesting finding is that the earliest sauropodomorphs, ancestors of the veggie long-necked sauropods like Diplodocus, were carnivores. This shows that herbivory was not ancestral for any of these two lineages, countering traditional hypotheses, and that the diets of early dinosaurs were quite diverse,” said study co-author Professor Emily Rayfield.

Dr. Ballell concluded: “It seems that one of the things that made the first dinosaurs special is that they evolved different diets throughout the Triassic, and we think this might have been key for their evolutionary and ecological success.”

By Alison Bosman, Staff Writer

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