A primeval giant with a low, elongated skull? That doesn’t quite correspond to our typical image of a predatory dinosaur. However, a preliminary examination of the inner structures of a Spinosaur skull indicates that it was quite a sophisticated specialist. This is the finding of a research project in which the University of Fribourg was a participant.
Spinosaurs are a group of large to gigantic predatory dinosaurs that were particularly widespread in the southern hemisphere. With a length of up to 18 m, Spinosaurus made even the famous Tyrannosaurus rex look small. It "only" made it to 12 m. In contrast to the massive, powerfully built skull of a Tyrannosaurus or Allosaurus, the elongated skull of Spinosaurus was comparatively narrow. For some time it has been suspected that Spinosaurs mainly fed on fish and similar smaller prey.
Largely unknown till now
Sensory organs and brain structure can provide valuable insights into the way an animal lives and functions. In the case of Tyrannosaurus rex it has been known for a long time that these animals had an excellent sense of smell, something which is certainly advantageous for a large predator. However only a few remains of Spinosaur skulls are known to us today. Many aspects of the cranial anatomy of these animals are therefore still unclear.
Making internal structures visible
The brain cavity and associated sensory organs of a Spinosaur were the subject of a preliminary investigation by Serjoscha Evers from the University of Fribourg and Marco Schade from the University of Greifswald together with Oliver Rauhut from the Bavarian State Palaeontology and Geology Collections in Munich. They examined the skull of the medium-sized Spinosaur Irritator which lived in Brazil during the lower Cretaceous Period, about 115 million years ago. In order to make the inner structures of the skull visible, for example the brain cavity and the inner ear, the petrified skull was x-rayed with a high-resolution computer tomography scanner at the German Heart Centre in Munich and at Zeiss Industrial Metrology in Essingen. The data thus obtained have enabled the reconstruction of the shape of the brain and its surrounding tissues, as well as the semicircular canals of the inner ear. These play an essential role in an animal’s balance and movement.
Fast, precise, deadly
The results showed that the shape of the Spinosaur brain was in fact quite similar to that of other large predatory dinosaurs. What was interesting, however, were the findings in relation to the inner ear and an associated region of the brain, the so-called flocculus. The latter’s main function in modern animals is in keeping the eyes steady during movements. It was considerably more pronounced in Irritator than in other large predatory dinosaurs. Together with the structure of the inner ear, it indicates that this animal was capable of performing fast, very precise movements with its skull without losing sight of potential prey.
These characteristics are of great advantage to an animal which has specialized in capturing smaller prey with rapid movements of the head. They thus support the view that Spinosaurs were more likely to have been predators specialized in catching smaller prey such as fish.