The tyrant emperor Tyrannosaurus imperator and the tyrant queen Tyrannosaurus regina have been added to the list of the most terrifying monsters to have ever walked the Earth, alongside the famous Tyrannosaurus rex (T-rex).
According to New Scientist, a new analysis by American paleontologists, based on 40 fossilized tyrannosaur skeletons, has revealed that Earth may have had up to 3 species of tyrannosaurs rather than just 1, each with distinct species-defining characteristics.
A team of experts from various museums, institutes, and universities across the United States, led by paleontologist Gregory S. Paul, found significant differences in the thigh bones of several tyrannosaur specimens. Some specimens exhibited an additional 1-2 slender incisors on each side of the jaw.
The famous dinosaur Sue is a T. imperator, not a typical T-rex – (Photo: Field Museum)
Specifically, some thigh bones were sturdier than others, while some had more slender structures. However, some females with slender thigh bones were found to be twice as robust as the “gentlest” specimens, indicating that the differences in bone structure were not due to sex, according to Daily Mail.
Results from dental examinations and the way specimens were excavated gradually helped to unravel the puzzle.
Among the Tyrannosaurus specimens examined, 29 were found in distinct sedimentary layers in the Maastrichtian, Lancian, North America, a “dinosaur sanctuary” known for its abundance of fossils.
Nine tyrannosaur skeletons were discovered in the lower layer, 3 at the lower-middle boundary, 4 in the middle layer, and 15 in the upper layer.
The 6 most robust females were found in the lower layer, with thigh bones similar to those found at other sites, indicating that there was only one species of Tyrannosaurus at that time. However, as the layers progressed upward, more distinct specimens with different thigh bones were found, suggesting that speciation was occurring.
From this, the authors classified Tyrannosaurus into 3 species:
- The first is Tyrannosaurus imperator – “tyrant emperor” – associated with specimens from the lower and middle sedimentary layers, characterized by extremely sturdy thigh bones and possessing 2 incisors.
- The second is “tyrant queen” Tyrannosaurus regina, associated with specimens from the upper and middle layers, characterized by more slender thigh bones and possessing 1 incisor.
- Meanwhile, the famous T-rex is found in the named sedimentary layer, recognized as a “latecomer” species, also possessing 1 incisor, but with healthier females.
Many famous tyrannosaur skeletons participated in the research. Among them, the dinosaur Sue from the Field Museum in Chicago was identified as T. imperator; while Stan, sold to a private buyer for $32 million in 2020, was identified as T. regina.
The study was recently published in the scientific journal Evolution Biology.
