New research indicates that Tyrannosaurus is actually three species – rex, imperator and regina

06 March 2022 16:54 STI

Washington [US]March 6 (ANI): According to a new analysis of Tyrannosaurus skeletal remains, physical differences have been revealed in the femur, other bones and dental structures between specimens that may suggest that Tyrannosaurus rex specimens should be reclassified into three distinct groups or species.
The study was published in the journal “Evolutionary Biology”.
Previous research has recognized the variation between Tyrannosaurus skeletal remains in the femur (thigh bone) and specimens with one or two thin incisors on either side of the anterior ends of the jaw.
Gregory Paul and his colleagues analyzed the bones and dental remains of 37 Tyrannosaurus specimens. The authors compared the sturdiness of the femur in 24 of the specimens, a measure calculated from length and girth that gives an indication of bone strength. They also measured the diameter of the base of the teeth or the space in the gums to determine if the specimens had one or two thin incisiform teeth.
The authors observed that the femur varied between specimens, some with more robust femurs and others with more slender femurs. The authors found that there were twice as many stout femora as slender femora among the specimens, suggesting that this is not a sex-caused difference, which would likely result in more splitting. equal. The authors also suggested that the variation in femora is unrelated to specimen growth, as stout femora have been found in some juvenile specimens at two-thirds the size of an adult and slender femora have been found in some specimens of adult size.
Tooth structure also varied between specimens, although those with both femur measurements and tooth remains were low (12 specimens). Specimens with an incisor tooth were correlated with an often higher femoral gracilis.

Of the Tyrannosaurus specimens, 28 could be identified in distinct layers of sediment (stratigraphy) in the Late Mastrichtian Late Formations in North America (estimated between 67.5 and 66 million years old). The authors compared Tyrannosaurus specimens with other theropod species found in lower sediment layers.
Only robust Tyrannosaurus femurs were found in the lower sediment layer (six femurs). The variation in femur robustness in the lower layer was no different from that of other theropod species, indicating that only one species of Tyrannosaurus probably existed at this point. A single Tyrannosaurus gracile femur has been identified in the middle layer with five other gracile femurs in the top layer, alongside other robust femurs. The variation in the sturdiness of the Tyrannosaurus femur in the upper sediment layer was higher than observed in some earlier theropod specimens. This suggests that Tyrannosaurus specimens found in the upper layers of sediment physically developed into more distinct forms compared to specimens from the lower layers and other dinosaur species.
Gregory Paul, lead author, said: “We found that changes in Tyrannosaurus femurs are unlikely to be related to sex or age of the specimen. We propose that changes in the femur may have evolved over time. time from a common ancestor that was more robust the femurs become more gracile in later species Differences in the robustness of femurs across sediment layers can be considered distinct enough that specimens can potentially be considered as separate species.
The authors named two potential new species of Tyrannosaurus based on their analysis. The first, Tyrannosaurus imperator (tyrant lizard emperor), concerns specimens found in the lower and middle layers of sediments, characterized by more robust femurs and usually two incisors. The authors argue that these features were carried over from earlier ancestors (tyrannosaurids).
The second, Tyrannosaurus regina (tyrant lizard queen), is related to upper and possibly middle sediment specimens, characterized by thinner femurs and an incisor tooth. The recognized species Tyrannosaurus rex (tyrant lizard king) has been identified in the upper and possibly middle layer of sediments with specimens classified as retaining sturdier femurs while having only one incisor tooth. Some specimens could not be identified based on their remains and therefore were not assigned to a species.
The authors acknowledged that they cannot rule out that the observed variation is due to extreme individual differences, or atypical sexual dimorphism, rather than separate groups, and they also cautioned that the location in the strata sediment is not known for some specimens. The authors discussed the difficulties of assigning fossil vertebrates to a potential new species.
The authors concluded that the physical variation found in Tyrannosaurus specimens combined with their stratigraphy points to three potential groups that could be designated as two new species, T. imperator and T. regina, alongside the only recognized species to date, T. rex. (ANI)

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