Dinosaurs evolved a remarkable diversity of dietary adaptations throughout the Mesozoic Era, but the origins of several dietary modes are uncertain, especially the multiple origins of herbivory. The feeding habits of early dinosaurs are largely inferred from qualitative comparisons of tooth morphology with extant analogs.

Paleobiologists at the University of Bristol investigated the dental morphofunctional diversity of early dinosaurs by looking at the tooth shapes, simulating their tooth function with computer models and comparing them to living reptiles and their diet.

They found that many groups of herbivorous dinosaurs were ancestral omnivores, and that the ancestors of our famous long-necked herbivores, such as Diplodocus, ate meat.

The earliest dinosaurs are mysterious because they were much smaller than their more recent descendants and spent most of the Triassic era in the shadow of reptiles that resembled crocodiles. Dinosaurs survived the mass extinctions of the Triassic and Jurassic and were able to adapt in their wake, becoming the dominant group for the rest of the Mesozoic Era. However, how diverse they were in nutrition and ecology is still being determined. Scientists believe that something must have happened in the Triassic that allowed this to happen.

Lead author Dr. Antonio Ballell from the University of Bristol said: “Soon after they emerged, dinosaurs begin to display an exciting diversity of skull and tooth shapes. For decades, this has led paleontologists to suspect that different species were already experimenting with different types of diets. They compared them to modern lizard species and tried to deduce what they ate based on the similarities in their teeth.

“We investigated this by applying a range of computational methods to quantify the shape and function of early dinosaur teeth and compare them to living reptiles with different diets. This included mathematically modeling their tooth shapes and simulating their mechanical responses to bite forces with engineering software.”

three major dinosaur genera
The three main dinosaur lines and their typical tooth shapes Antonio Ballell

Professor Mike Benton, a co-author of the study, said: “This set of methods allowed us to numerically quantify how similar early dinosaurs were to modern animals, providing solid evidence for our conclusions about diets. Theropod dinosaurs have pointed, curved, and blade-like teeth with small serrations, which behave like those of modern monitor lizards In contrast, the serrated teeth of ornithians and sauropodomorphs more closely resemble modern omnivores and herbivores, such as iguanas.”

Professor Emily Rayfield, a senior co-author, said: “Our analyzes show that ornithischians – the group that includes many herbivorous species, such as the horned dinosaurs, the armored ankylosaurs and the duck-billed dinosaurs – started out as omnivores. And another interesting finding is that the earliest sauropodomorphs, ancestors of the vegetarian long-necked sauropods like Diplodocus, were carnivores. This shows that herbivory was not ancestral to either of these two lineages, which contradicts traditional hypotheses and that the diets of early dinosaurs were quite diverse.”

Dr. Ballell concluded: “It seems that one of the things that made the early dinosaurs special is that they evolved different diets during the Triassic period. We think this may have been key to their evolutionary and environmental success.”

Magazine reference:

  1. Antonio Ballel et al. Tooth shape and function in early dinosaur dietary diversification. Scientific progress. DOI: 10.1126/sciadv.abq5201