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Irritator challengeri: A new look at a spinosaurid dinosaur

Irritator challengeri, a spinosaurid dinosaur, was a two-legged, carnivorous creature. Our understanding of this species comes from the most complete fossil skull discovered from its group. Paleontologists from Greifswald, Munich, Alkmaar, and Fribourg used X-ray computed tomography, typically employed in medicine and material science, to extensively examine the fossil and made remarkable findings.

It is believed that Irritator hunted relatively small prey in what is now Brazil. The species had a snout that evolved to close rapidly and had a surprising feature: when the predator opened its mouth, the lower jaws spread out sideways, widening the throat region. The research on this topic was published in Palaeontologia Electronica.

Marco Schade, an expert in dinosaur fossils, has dedicated several years to studying these extinct creatures. Since these organisms became extinct millions of years ago, we often have only incomplete fossils remaining. These remains are usually housed in public collections, such as the Staatliches Museum für Naturkunde Stuttgart, and occasionally provide unexpected insights into life on our planet during long-gone eras.

Spinosaurids are among the largest land predators ever to have lived on Earth. Their distinct anatomy and limited fossil record make them mysterious compared to other large carnivorous dinosaurs. Spinosaurids have long and slender snouts with numerous conical teeth, robust arms with impressive claws, and elongated processes on their spines.

The most complete fossil skull of a spinosaurid belongs to Irritator challengeri, which was discovered in sedimentary rocks approximately 115 million years old in eastern Brazil. Estimated to have reached a length of around 6.5 meters, this species was the largest animal in its ecosystem. The same region also yielded fossils of other dinosaurs, pterosaurs, crocodile relatives, turtles, and diverse fish species.

In their recent study, scientists meticulously reconstructed each bone of the fossil skull and assembled them in their original position to understand the unique characteristics of spinosaurids. By using CT scans, they determined that Irritator likely held its snout at an inclined angle of about 45 degrees in situations that required heightened awareness of its surroundings. This positioning provided three-dimensional vision to the front, as the long muzzle did not obstruct the field of view from both eyes.

Moreover, Irritator's skull was evolutionarily adapted to deliver a relatively weak but incredibly fast bite. When the predator opened its mouth, the lower jaws spread out sideways, expanding the pharynx. This mechanism is somewhat comparable to the feeding behavior of pelicans, although the biomechanical processes involved differ. These observations suggest that Irritator preferred relatively small prey, including fish, which it swiftly snapped up, inflicting severe injuries with rapid jaw movements to enable swift swallowing of its prey whole.

Verified spinosaurid fossils are exclusively found in the Early and Late Cretaceous periods, spanning approximately 35 million years. This timeframe aligns with the evolutionary gap between spinosaurids and other large predatory dinosaurs. The study provides fresh insights into the lifestyle of spinosaurids, demonstrating that they acquired numerous new anatomical features within a relatively short geological timeframe, ultimately transforming them into the highly specialized and exceptional dinosaurs we recognize today.

Source: Universität Greifswald

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