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Tyrannosaurs rex evolved sensitive lower jaws, a feature seen in some modern-day animals, but never before observed in dinosaurs. The discovery could indicate one of a range of behaviors we don't normally associate with the fearsome carnivores, such as parental care, although it also probably made them even more effective killers.
Dr Soichiro Kawabe and Dr Soki Hattori of Fukui Prefectural University CT-scanned a T. rex lower left jawbone from the Hell Creek Formation, Montana. In Historical Biology, they report a more complex distribution of nerves than previously detected in dinosaurs, that matches crocodiles and foraging birds like ducks. The nerves themselves are long gone, but the canals in which they were housed can still be mapped. Although only the lower jaw was studied, it is anticipated the upper jaw was similarly nervous.
“What this means is that T. rex was sensitive to slight differences in material and movement; it indicates the possibility that it was able to recognize the different parts of their prey and eat them differently depending on the situation,” Kawabe said in a statement. “This completely changes our perception of T. rex as a dinosaur that was insensitive around its mouth ... biting at anything and everything including bones.” Previous research has suggested the giant tyrannosaurid Tarbosaurus was selective about the parts of its prey it ate, so this may have been a widespread trait.
Whether T. rex left the bones of its meal for scavengers was probably of limited interest to its prey, and perhaps even to most dinosaur enthusiasts. However, the sensitive jaw may also be indicative of other behavior. “In addition to predation, tyrannosaurids’ jaw tips were adapted to perform a series of behaviors with fine movements including nest construction, parental care, and intraspecific communication,” the paper concludes.
This sensitivity could be useful in so many ways it's hard to be certain which actually occurred. Nevertheless, we might need to get used to the idea of T. rexes gently caring for their young and maybe even bonding with mates by nuzzling if we want a true Cretaceous picture. At least they probably weren't feathered as well.
The findings were not a total surprise, since another tyrannosaurid Daspletosaurus also appeared to have a more sensitive facial area than other dinosaurs studied in this way, such as Triceratops and Edmontosaurus. Even Neovenator, a theropod more distantly related to T. rex, shows signs of a sensitive upper jaw.
Many viewers of Jaws confidently opined that the way to fight off giant sharks was to punch them on their sensitive noses, though few have actually reported success in this approach. Perhaps, if confronted with a Jurassic Park situation, one might try hitting the T. rex's jaw to see if it retreats in agony. If you think that sounds stupid, let's hear your better idea.
