Tyrannosaurus remains hint at two possible species distinct from T. rex

A new analysis of the bones of the tyrannosaurus rex shows that there are physical differences that need to be re-categorized.

The only recognized species of dinosaurs is the tyrannosaurus rex. There is variation across the bones of the tyrannosaurus rex with either one or two slender incisor teeth on each side of the jaw.

Gregory Paul and colleagues analyzed the bones and dental remains. The authors compared the strength of the bone in 24 of the samples, using a measure that is calculated from the length and circumference. They measured the size of the base of teeth and the space in the gums to see if there were any slender incisiform teeth.

Some of the femurs were more robust and others were more gracile. The authors found that there were two times more robust femurs than gracile ones, which suggests that this is not a difference caused by sex, which would likely result in a more even split. The authors suggest that the variation in femurs is not related to growth of the specimen, as robust femurs were found in some juvenile specimen two thirds the size of an adult and gracile femurs were found in some specimen that were full adult size.

The dental structure was different for each specimen, although those with both femur measurements and dental remains were low. Specimens with one incisor tooth had higher femur gracility.

The tyrannosaurus rex could be identified in distinct layers of sediment at the Lancian upper Masstrichtian formations in North America. The authors compared the tyrannosaurus rex with other tyrannosaurus rex species.

There were six femurs found in the lower layer of the sediment. The variation of femur robustness in the lower layer was not different to that of other theropod species. There were only one gracile and five other robust femurs in the middle layer. The tyrannosaurus rex's robustness was higher in the top layer of the fossils than it was in the earlier ones. This suggests that the tyrannosaurus rex fossils found at higher layers are more distinct than those found at lower layers.

The changes in the dinosaur are not related to the specimen's age or sex. The changes in the femur may have evolved from a common ancestor who displayed more robust femurs to become gracile in later species. The differences in femur robustness may be considered distinct enough that they could be considered separate species.

Two new species of tyrannosaurus are nominated by the authors. The firstTyrannosaurus imperator is a tyrant lizard emperor, which is characterized by more robust femurs and two incisor teeth. The features have been retained from earlier ancestors. The second tyrant lizard queen is linked to specimen from the upper and possibly middle layers of the site. The tyrant lizard king is a recognized species that has one incisor tooth, but retains more robust femurs. Some specimen were not assigned a species because they couldn't be identified based on their remains.

The authors acknowledge that they can't rule out that the observed variation is due to extreme individual differences, or atypical sexual dimorphism, rather than separate groups, and they caution that the location within the layers is not known for some specimen. Difficulties of assigning fossil vertebrates to a new species are discussed by the authors.

The authors conclude that there are three groups that could be nominated for a new species.

More information: Gregory Paul, The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus, Evolutionary Biology (2022). DOI: 10.1007/s11692-022-09561-5. link.springer.com/article/10.1 … 7/s11692-022-09561-5 Journal information: Evolutionary Biology Citation: Tyrannosaurus remains hint at two possible species distinct from T. rex (2022, March 1) retrieved 1 March 2022 from https://phys.org/news/2022-03-tyrannosaurus-hint-species-distinct-rex.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.