A new analysis of Tyrannosaurus skeletal remains reveals physical differences in the femur, other bones and dental structures across specimens that could suggest Tyrannosaurus rex specimens need to be re-categorized into three distinct groups or species, reports a study published in Evolutionary Biology.
and specimens with either one or two slender incisor teeth on each side of front ends of the jaw.
The authors observed that the femur varied across specimens, some with more robust femurs and others with more gracile femurs. The authors found there were two times more robust femurs than gracile ones across specimens, which suggests that this is not a difference caused by sex, which would likely result in a more even split.
Only robust Tyrannosaurus femurs were found in the lower layer of sediment . The variation of femur robustness in the lower layer was not different to that of other theropod species, which indicates that likely only one species of Tyrannosaurus existed at this point. Only one gracile Tyrannosaurus femur was identified in the middle layer with five other gracile femurs in the upper layer, alongside other robust femurs.
The authors nominate two potential new species of Tyrannosaurus based on their analysis. The first, Tyrannosaurus imperator , relates to specimens found at the lower and middle layers of sediment, characterized with more robust femurs and usually two incisor teeth. The authors argue these features have been retained from earlier ancestors .
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