They compared Tyrannosaurus specimens collected throughout North America with almost all single-species dinosaur specimens, such as 14 alosor specimens collected from the Cleveland-Lloyd dinosaur quarry at the University of Utah. Tyrannosaurus rex, they explained, differ greatly in body proportions, indicating that they may belong to different species.

Some specimens were difficult to classify, but 26 of them seemed to fit into three types, Paul suggests: a stocky morphology of early Cretaceous was found with two sets of incisions in the lower jaw in the Hell Creek formation. A set of solid, beautiful wounds.

Paul and colleagues came to the conclusion that these three forms could be different from each other – they appeared in a frame long enough to give them different names. Hence, the name given to the largest and oldest morphotype of Tyrannosaurus found in Hell Creek. Emperor Tyrannosaurus (“Dictator Emperor Lizard”), which later — within one or two million years — was strongly divided. Tyrannosaurus rex Newly named and relatively thin, Tyrannosaurus regina (Queen dictator lizard).

That proposed evolutionary path – from a tank-like population to a relatively dynamic one – corresponds to the early Cretaceous habitat dominated by Tyrannosaurus relatives, Paul explained. In those days, like big animals Daspletosaurus Associated with hunters with long legs like Gorgosorus.

In Holtz’s opinion, this idea is completely credible, but it needs the support of future discoveries to test it.

“This is a theory that can be tested, because there must be no claim to species identity,” Holts said. “With more new models, we’ll be able to see if models we do not include or have not yet found comply with or reject this proposal.”

Although Holtz thought that the authors’ argument would be more convincing if the different species they describe were arranged over specific rock layers, there were other examples of species variation in the formation of Hell Creek. The other fossils found there led to the general conclusion that there were more than one species of trisaratopes, Holts said. The domed hadrosers and pachycephalosores found at the top of the formation may differ significantly from the ones below.