It cleverly adapted to hunting: When the spinosaur Irritator Challengeri opened its snout while hunting, it spread its mandibular structures, thus expanding its pharynx, a digital skull reconstruction suggests. Anatomical evidence also shows that the Irritator kept its head down while hunting and slashed relatively weakly but quickly. Paleontologists say that in this way he apparently captured small aquatic animals in Cretaceous South America.
Weird, amazing, and mysterious: Because of their unusual characteristics, spinosaurs became celebs of the Cretaceous animal world. Their discovery dates back to 1912: Spinosaurus aegyptiacus from North Africa was the first to enter the paleontological scene. This predatory dinosaur was more than 16 meters long, had long limbs on its vertebrae and an elongated snout like that of a crocodile. Meanwhile, it was proved that it represented a very large group of predatory dinosaurs, for which it gave its name: in addition to North Africa, species of Cretaceous predatory dinosaurs that can be assigned to the group Spinosaurus were also discovered in Europe, Australia, North and South America.
Various studies have already shown that the unusual features of this group of dinosaurs are due to adaptation to life on or in the water. They seem to feed on fish and other aquatic creatures. However, skull fossils have so far been able to provide relatively little information about these animals, because there are very few finds of these structures. The best-preserved skull is a find from an approximately 115-million-year-old bedrock in eastern Brazil and is kept at the State Museum of Natural History in Stuttgart. The fossil, about 85 cm long, comes from Spinosaurus Irritator Challengeri. At about 6.50 meters long, it was relatively small. However, it had similar basic characteristics to those of the giant Spinosaurus aegyptiacus.
X-ray and biomechanical analysis
However, even the most complete Spinosaurus skull fossil known has remained a mystery. Because the poor state of preservation has not yet allowed any detailed insights. An international team of paleontologists led by Marco Schade of the University of Greifswald examined the skull remains with the help of X-ray computer tomography used in medicine and materials research. In this way, scientists were able to work out individual bones and draw conclusions about missing parts. They then used the results to develop a 3D reconstruction of the skull. This also reversed earlier muscular structures.
As reported by paleontologists, the skull model provided interesting information about the animal’s behavior and adaptations. Biomechanical models therefore suggest that when an irritant opens its mouth, some of the bony structures in the mandible spread outward due to the shape of the jaw joint. In this way, the pharynx of the animal was expanded, the scientists explained. Although the mechanism differs, the concept is thus similar to the expansion of the gollary pouch in pelicans, the University of Greifswald writes in its communication about the study.
Adaptations for hunting in the water
Biomechanical evidence also shows that irritant has poor bite force compared to other large predatory dinosaurs. However, the findings suggest that the musculature and structure of the mouth probably allow for very rapid movements of the jaw. The researchers report that the anatomy of the skull also gives an indication of the position of the animal’s head: When hunting, the narwhal appears to tilt its nose downward about 45 degrees so that it can see three-dimensionally in front of it. Because only with this position there are no annoying structures obstructing the field of view.
As the team summarizes, the results again show adaptations to an aquatic lifestyle in this representative of spinosaurids. It apparently preyed on small aquatic prey such as fish, whose anatomical characteristics and mechanisms enabled it to be effectively grasped and rapidly swallowed. Findings from the site where Irritator was found also fit in with this: the dinosaur lived there in a lake landscape where many species of fish were found.
Information about the anatomy of the skull has also provided new clues about the evolutionary history of spinosaurs, the paleontologists report. Because it opened up new possibilities for comparison with other predatory dinosaurs. “The new study provides a better understanding of how spinosaurs lived and shows that, relative to other carnivorous dinosaur lineages, they evolved anatomical features very quickly during their evolution, eventually resulting in particularly specialized and different dinosaurs,” writes the University of Greifswald graduate.
Source: University of Greifswald, specialized article: Palaeontologia Electronica, doi: 10.26879/1242
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