Irritator challengeri belongs to the bipedal carnivorous dinosaurs, more precisely: to the spinosaurs.
Irritator has the world’s most completely preserved fossil skull of a spinosaur.
With the help of X-ray computer tomographs from the fields of medicine and materials research, scientists from Greifswald (Germany), Munich (Germany), Alkmaar (Netherlands), and Fribourg (Switzerland) have now conducted in-depth studies on this fossil and made some astonishing discoveries.
With downward tilted, fast closing jaws, Irritator probably hunted relatively small prey in what is now Brazil.
A minor sensation for the experts: when the animal opened its snout, the lower jaw branches spread apart laterally, widening the throat.
Palaeontologia Electronica has published the study.
Marco Schade has been working with dinosaur fossils for several years.
The animals he studies have been extinct for millions of years, and their remains are often not fully preserved.
Their fossils are often stored in public collections – as in this case at the Staatliches Museum für Naturkunde Stuttgart – and provide insights into times long past.
Spinosaurs are among the largest land-dwelling predators in the history of the Earth.
Compared to other large predatory dinosaurs, many questions about their striking anatomy have remained unanswered until now; the rather sparse fossil finds usually provided few clues about their lifestyle and evolutionary history.
Spinosaurs have comparatively long, slender snouts with numerous conical teeth, powerful arms with impressive claws, and sometimes very long appendages on their spines.
The most preserved spinosaur skull is from an Irritator found in eastern Brazil’s 115 million-year-old rock layers.
While the species, with an estimated body length of 6.5 meters, is considered the largest animal from its ecosystem, other dinosaurs, pterosaurs, crocodile relatives, turtles, and numerous fish species are known.
For their study, the paleontologists reconstructed each skull bone in the fossil and placed them back in their original positions to discover what makes spinosaurs special.
Using the CT data, the researchers found that Irritator probably kept its snout tilted downward by about 45° in attention-demanding situations, realizing a range of three-dimensional vision to the front.
Only when the snout was held at a steep tilt were no interfering structures on the animal’s head that would have obstructed a clear field of view.
In addition, Irritator‘s skull was designed so that the species – compared to other large predatory dinosaurs – could only exert a weak biting force but could close its jaws extremely quickly.
During this process, due to the shape of the mandibular joint, the mandibular branches also spread outward, widening the animal’s maw – similar to modern pelicans but triggered by a different mechanism.
This is evidence that Irritator stalked relatively small prey, including fish, seized them with rapid jaw movements, severely injured them, and swiftly gagged them down.
Secure spinosaur fossils date exclusively from the Early and Late Cretaceous and span about 35 million years.
Their evolutionary history is separated from other predatory dinosaurs by the same length of time, without our knowledge of corresponding fossils from that period.
The new study provides a better understanding of how spinosaurs lived and shows that, relative to other predatory dinosaur lineages, they rapidly acquired more new anatomical features during their evolution, eventually allowing them to become the specialized and different dinosaurs we know today.
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