Experts say there is enough variation in samples to argue there was also a Tyrannosaurus imperator and a regina
With its immense size, dagger-like teeth and sharp claws, Tyrannosaurus rex was a fearsome predator that once terrorised North America. Now researchers studying its fossils have suggested the beast may not have been the only tyrannosaurus species.
Paul and colleagues studied a total of 37 specimens attributed to T rex, in particular looking at the length and circumference of the thigh bones, available for about two-thirds of the specimens, to assess their robustness. The team say the variation does not appear to be linked to the overall size of the specimen or how mature the animal was when it died, while other factors – such as the uneven ratio of more robust bones to those that were more slender, or “gracile” – suggests such variation is unlikely to be linked to the sex of the beasts.