Although some giant meat‑eating dinosaurs like tyrannosaurids famously evolved skulls optimized for incredibly powerful, bone‑crushing bites, others, like the megalosauroids and allosauroids, relied on lighter, faster, slashing-style jaws. A new study in Current Biology reveals that large carnivorous dinosaurs adopted different biomechanical strategies to meet the demands of predation.
A research team led by Andre J. Rowe at the University of Bristol used biomechanical modeling to analyze skulls of 18 carnivorous dinosaur species. Their findings show that, unexpectedly, the giant theropod dinosaurs used different strategies for hunting. In tyrannosaurs, skull stress went up as they got bigger, mainly because their jaw muscles and bite forces became much stronger. However, in other large theropods, i.e. megalosaurs, allosaurs and spinosaurs, their skulls did not face more stress as their size increased. When the skulls of smaller theropods were scaled to equivalent size, they experienced higher stresses.
“There wasn’t one ‘best’ skull design for being a predatory giant; several designs functioned perfectly well.” said senior author Andre Rowe of the University of Bristol, UK.
The study underscores that even within apex predators, there was considerable variation in feeding mechanics. This points to a richer ecological diversity and specialization than previously appreciated.
Methodology
Earlier studies have looked at how size affects movement, we still don’t fully understand how the biomechanics of feeding works. In living diapsids, bite force tends to increase with body mass. However, many older studies on theropod feeding relied on 2D skull shapes, which don’t capture the full complexity of their anatomy. Some key questions remain: As body size increases, does the skull handle stress better just because of its shape (geometric scaling)? Or do larger muscles create proportionally greater forces, leading to more stress on the skull? And does skull shape evolve to help manage or reduce these forces?
To explore this, Rowe and his colleague Emily Rayfield used finite element analysis (FEA) to study the relationship between body size and skull biomechanics in 18 theropod species. These mainly included members of three major groups that each evolved large body size on their own, Megalosauridae, Allosauroidea, and Tyrannosauroidea. The study also included smaller basal theropod dinosaurs like Herrerasaurus and Dilophosaurus for comparison. The study excluded plant-eating theropods like therizinosaurs, since their skulls had unique features, like different tooth shapes and muscle arrangements, designed for herbivory.
Findings
While stress magnitudes in all species remained within biomechanically tolerable limits, the greatest cranial stress resistance was observed in the giant non-tyrannosauroid theropods, particularly megalosauroids and allosauroids such as Spinosaurus and Acrocanthosaurus. On the other hand, tyrannosauroids showed higher cranial stress levels.
These results reveal two divergent functional strategies among giant theropods:
- A low stress, lower-power strategy – typified by allosauroids and megalosauroids, whose slenderer skulls and more distributed muscle loading reduce peak stresses; and
- a high-stress, high-power strategy – represented by tyrannosaurids, whose skulls allow for greater adductor muscle mass and stronger, bone-crushing bites.
Conclusions
This suggests that large theropods evolved in two different ways: either they got bigger while keeping stress low, or they developed more powerful jaws and muscles, even if it meant putting more strain on their skulls. Tyrannosaurs were unique in belonging to the second category because they went all-in on stronger bites, even though it meant more stress on their heads. This might have helped them catch larger, faster prey in the Late Cretaceous. Another reason could be that they were competing with other predators like smaller theropods or giant crocodile-like animals.
“I tend to compare Allosaurus to a modern Komodo dragon in terms of feeding style,” Rowe said “Large tyrannosaur skulls were instead optimised 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.”