King, Queen, Emperor: The 3 Different Dinosaur Species Of T. rex. All About It
Researchers have nominated two new potential dinosaur species alongside Tyrannosaurus rex or tyrant lizard king. These are: tyrant lizard emperor and tyrant lizard queen.
New Delhi: Tyrannosaurus rex (T. rex), one of the most ferocious predators to ever walk the Earth, may have been three different dinosaur species, not one, a new study has found.
The study, led by United States researchers, was recently published in the journal, Evolutionary Biology.
The researchers analysed Tyrannosaurus skeletal remains as part of the study. The analysis revealed physical differences in the femur, other bones, and dental structure across specimens, according to the study.
These differences could suggest that T. rex specimens need to be re-categorised into three distinct groups or species.
To date, T. rex is the only recognised species of the genus Tyrannosaurus.
Scientists, in previous research, have acknowledged variation across Tyrannosaurus skeletal remains in the femur, and in specimens with either one or two slender incisor teeth on each side of front ends of the jaw.
Analysing Tyrannosaurus skeletal remains
Gregory S Paul, the lead author of the study, along with his colleagues, analysed the bones and dental remains of 37 Tyrannosaurus specimens as part of the study. The researchers compared the robustness of the femur in 24 of the specimens. This measure is calculated from the length and circumference of the figure, and gives an indication of the strength of the bone.
The authors also measured the diameter of the base of teeth or space in the gums to assess if specimens had one or two slender incisiform (having the shape of an incisor tooth) teeth.
Variations In Femurs
The study found the femur varied across specimens. Some specimens had more robust femurs, and others had more gracile femurs.
It was also observed that there were two times more robust femurs than gracile ones across specimens. This suggests that the difference is not caused by sex, which would likely result in a more even split, the study said.
The authors noted in the study that the variation in femurs is not related to growth of the specimen. This is because robust femurs were found in some juvenile specimens that are two-thirds the size of an adult. Also, gracile femurs were found in some specimens that were full adult size, the study said.
Variations In Dental Structures
Variations in dental structure across specimens were also observed. According to the study, specimens with one incisor tooth were correlated with often having higher femur gracility.
As many as 28 Tyrannosaurus specimens could be identified in distinct layers of sediment (stratigraphy) at the Lancian upper Masstrichtian formations in North America, the study said. These formations are estimated to be from between 67.5 to 66 million years ago. Stratigraphy is the scientific discipline concerned with the description of rock successions and their interpretations in terms of a general time scale.
Comparing Tyrannosaurus With Other Theropods
Tyrannosaurus specimens were compared with other theropod species found in lower layers of sediment. The study found only robust Tyrannosaurus femurs in the lower layer of sediment. There were six femurs in that part of the sediment.
The authors found that the variation of femur robustness in the lower layer was not different to that of other theropod species. This indicates that likely only one species of Tyrannosaurus existed at that point, the study said.
In the middle layer, only one gracile Tyrannosaurus femur was identified. Five other gracile femurs were identified in the upper layer, alongside other robust femurs, the study said.
The variation in Tyrannosaurus femur robustness in the top layer of the sediments was higher than what was observed in some earlier theropod specimens, suggesting that the Tyrannosaurus specimens found at higher layers of sediment physically developed into more distinct forms compared to specimens from lower layers, and other dinosaurs species, according to the study.
In a statement issued by academic publishing company Springer, Gregory Paul said that the researchers found that the changes in Tyrannosaurus femurs are likely not related to the sex or age of the specimen.
The authors proposed that the changes in the femur may have evolved over time from a common ancestor who displayed more robust femurs to become more gracile in later species.
Paul said that the differences in femur robustness across layers of sediment may be considered distinct enough that the species could potentially be considered separate species.
Tyrant Lizard King, Queen And Emperor
The researchers nominated two potential new species of Tyrannosaurus based on their analysis, the study said. The first species, Tyrannosaurus imperator (tyrant lizard emperor), relates to specimens found at the lower and middle layers of sediment. The tyrant lizard emperor is characterised by more robust femurs and usually two incisor teeth.
The authors argued in the study that these features have been retained from earlier ancestors (tyrannosaurids).
According to the study, the second species, Tyrannosaurus regina (tyrant lizard queen), is linked to specimens from the upper and possibly middle layers of the sediment, characterised by slenderer femurs and one incisor tooth.
The study said that the recognised Tyrannosaurus rex (tyrant lizard king) was identified in the upper and possibly middle layer of sediment with specimens classed as retaining more robust femurs while having only one incisor tooth.
The authors said that some specimens could not be identified based on their remains, so were not assigned to a species.
According to the authors, the observed variation is due to extreme individual differences, or atypical sexual dimorphism (systematic difference in form between individuals of different sex in the same species), rather than separate groups.
The authors cautioned that the location within sediment layers is not known for some specimens, and discussed the difficulties of assigning fossil vertebrates to a potential new species.
The researchers concluded that the physical variation found in Tyrannosaurus specimens combined with their stratigraphy are indicative of three potential groups that could be nominated as two new species, T. imperator and T. regina, alongside the only recognised species to date, T. rex.
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