Surprising study finds ancestors of most herbivorous dinosaurs ate meat
A comprehensive new study has examined the diets of the earliest dinosaurs and found that, unsurprisingly, they included carnivores, herbivores and omnivores. But what is surprising is that the ancestors of many of the most famous herbivores – like Triceratops and Brachiosaurus – originally ate meat.
When you picture dinosaurs, most people think of the classic giants – the fearsome Tyrannosaurus rex, the horned Triceratops, or the long-necked Brachiosaurus. But these iconic species all arose fairly late in the game, towards the end of the dinosaurs’ reign on Earth – when they first evolved about 170 million years earlier, they were generally much smaller.
Not as much is known about these early dinosaurs, including what many species ate. So for the new study, researchers at the University of Bristol investigated the eating habits of 11 early species from the three main lineages – ornithischians, sauropodomorphs and theropods.
The biggest clue to an extinct animal’s diet is its teeth. Carnivores have pointed teeth like butcher’s knives, to help them pierce and tear through flesh, while herbivores usually have broad, flat teeth that help them grind up plant matter. And this is how the Bristol scientists conducted their study.
“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. Antonio Ballell, lead author of the study. “This included mathematically modeling their tooth shapes and simulating their mechanical responses to biting forces with engineering software.”
From this, the team found fairly compelling evidence for the diverse diets of these early dinosaurs, including carnivores, herbivores and omnivores. The early theropods, for instance, had pointed blade-like teeth similar to the mostly meat-eating modern monitor lizards – this isn’t entirely surprising, given that later theropods included famous carnivores like T-rex and the raptor family.
But the more unexpected news came from the other two groups. While both later developed into a diverse range of herbivores, it seems that many of their ancestors started out eating meat in some form.
“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,” said Professor Emily Rayfield, senior co-author of the study. “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.”
This dietary diversity is likely what allowed the dinosaurs to thrive for so long, the team says. When they first arose, they were playing second fiddle to another big group of reptiles, but after a major extinction event at the end of the Triassic period, dinosaurs were successful and diverse enough to take over many now-empty niches.
“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,” said Ballell.
The research was published in the journal Science Advances.
Source: University of Bristol