While the Tyrannasaurus rex skull was optimized for quick, strong bites like a crocodile, other giant, predatory dinosaurs that walked on two legs—including spinosaurs and allosaurs—had much weaker bites and instead specialised in slashing and ripping flesh.
The new study, led by the University of Bristol and published in Current Biology today [5 August], demonstrates that meat-eating dinosaurs followed different evolutionary paths in terms of skull design and feeding styles.
Dr Andre Rowe, Senior Research Associate in the School of Earth Sciences at the University of Bristol, said: “Carnivorous dinosaurs took very different paths as they evolved into giants in terms of feeding biomechanics and possible behaviors.”
“Tyrannosaurs evolved skulls built for strength and crushing bites, while other lineages had comparatively weaker but more specialized skulls, suggesting a diversity of feeding strategies even at massive sizes. In other words, there wasn’t one ‘best’ skull design for being a predatory giant; several designs functioned perfectly well.”
Dr Rowe has always been fascinated by big carnivorous dinosaurs, and he considers them interesting subjects for exploring basic questions in organismal biology. In this study, he and co-author Professor Emily Rayfield, Professor of Paleobiology at the University of Bristol, wanted to know how bipedalism—or walking on two legs —influenced skull biomechanics and feeding techniques.
It was previously known that despite reaching similar sizes, predatory dinosaurs evolved in very different parts of the world at different times and had very different skull shapes. For Rowe and Rayfield, those facts raised questions about whether their skulls were functionally similar under the surface or if there were notable differences in their predatory lifestyles. As there are no massive, bipedal carnivores alive today—ever since the end-Cretaceous mass extinction event—the researchers note that studying these animals offers intriguing insights into a way of life which has since disappeared.
To examine the relationship between body size and skull biomechanics, the authors used 3D technologies including CT scans and surface scans analyse the skull mechanics, quantify the feeding performance, and measure the bite strength across 18 species of therapod, a group of carnivorous dinosaurs ranging from small to giant. While they expected some differences between species, they were surprised when their analyses showed clear biomechanical divergence.
“Tyrannosaurids like T. rex had skulls that were optimised for high bite forces at the cost of higher skull stress,” Dr Rowe explained. “But in some other giants, like Giganotosaurus, we calculated stress patterns suggesting a relatively lighter bite. It drove home how evolution can produce multiple 'solutions' to life as a large, carnivorous biped.”
Skull stress didn’t show a pattern of increase with size. Some smaller therapods experienced greater stress than some larger species due to increased muscle volume and bite forces. The findings show that being a predatory biped didn’t always equate to being a bone-crushing giant. Unlike T. rex, some dinosaurs, including the spinosaurs and allosaurs, became giants while maintaining weaker bites more suited for slashing at prey and stripping flesh.
“I tend to compare Allosaurus to a modern Komodo dragon in terms of feeding style,” Dr Rowe said. “Large tyrannosaur skulls were instead optimized like modern crocodiles with high bite forces that crushed prey. This biomechanical diversity suggests that dinosaur ecosystems supported a wider range of giant carnivore ecologies than we often assume, with less competition and more specialisation.”
This research was supported by funding from the Biotechnology and Biological Sciences Research Council.
Paper
'Carnivorous dinosaur lineages adopt different skull performances at gigantic size' by Andre Rowe and Emily Rayfield in Current Biology [open access]