Meat eating dinosaurs like Tyrannosaurus rex had eyes that seemed tiny in relation to the size of their heads. There were solid reasons for this, as the paleobiologist Stephan Lautenschlager from the University of Birmingham found out. The bony orbit (the cranial fossa in which the eye lies) was narrowed and reduced in these animals, which was associated with a higher load-bearing capacity of the skull. As a result, they could bite with enormous force. Lautenschlager reports on this in the journal Communications Biology.
The researcher examined fossils of various dinosaur and reptile species from the Mesozoic. It turned out that the early species mostly had circular or elliptical eye sockets. However, in the late Mesozoic, carnivores appeared with the cranial fossa shaped like a keyhole. belonged to them T. rex.
Huge and not vegetarian
Apparently, this shape change had something to do with body size: it occurred in animals whose heads were more than a meter long. It was also related to diet, since almost all species with keyhole-like eye sockets were carnivores.
© Stephan Lautenschlager, University of Birmingham (detail)
In the eye of T. rex | Skull shape (top) and reconstructed appearance (bottom) of Tyrannosaurus rex. The original skull with a keyhole-shaped eye socket can be seen at the top left. The eyeball only claimed the upper bulge and was therefore relatively small (bottom left). If the animals had kept a circular eye socket throughout their lives and if this had grown proportionally, it would have been significantly larger in the fully developed animal (top right). The eyes would then have been considerably more impressive (bottom right).
Using computer models, Lautenschlager calculated how the forces are distributed in the bone when compressive and tensile loads act on the structure of the dinosaur skull. In doing so, he assumed different shapes for the eye sockets and calculated the mechanical stresses that would occur in each case. Skulls with keyhole openings performed better in virtually all stress tests—whether they were crushed or bent vertically or horizontally.
© Stephan Lautenschlager, University of Birmingham (detail)
More stability thanks to narrowing | Computer simulation of the forces occurring in a hypothetical dinosaur skull. The colors indicate the mechanical load (yellow=high, blue=low). With a circular eye socket (above), the bone is exposed to higher stresses than with a keyhole-shaped one (below).
Calculations specifically for the physique of the T. rex revealed: Thanks to its narrowed eye sockets, the mechanical stress in the bone tissue decreased when the animal bit, and the head deformed less. In everyday life at that time, this was probably urgently needed: T. rex closed its jaws eight to 10 times more forcefully than today’s crocodiles, studies have shown. This corresponded to a weight of several tons per tooth.