T. Rex May Have Actually Been 3 Species, According to a Close Look at The Bones

The most famous prehistoric predator is the enormous colossus and predatory beast, the tyrannosaurus rex. It's place in the popular imagination is mirrored in the research that goes into it.

All of the adult fossils from the plains of Canada to the southwestern United States belong to a single species: the T. rex.

Scientists have known about the differences in the bones of the dinosaurs for a long time, most notably the thigh bone in larger individuals and the incisor teeth at the front of the jaw.

When male and female members of the same species appear different, it's called sexual dimorphism. Individuals being at different stages of genetic development is one of the explanations for the differences.

The most intriguing explanation is that these differences represent distinct species within the genera tyrannosaurus.

The bones and dental remains of 38 tyrannosaurus rex were studied by paleontologists. They compared the femur bones in 24 of the specimen to see if they were strong. The individuals were measured to see if they had one or two incisor teeth.

The degree of robustness appeared to have no relationship with the size of the specimen, suggesting that older, bigger individuals have stronger bones. Some of the largest specimen had bones that were more slender and curved.

The differences were not down to sexual dimorphism, where you would expect a more even distribution.

Twenty-nine of the tyrannosaurus rex fossils were found in the Lancian upper Maastrichtian formations in North America, which are thought to be from 67.5 to 66 million years ago.

There are three levels of these sediments: lower, middle, and upper. Only one gracile femur was found in the middle, and in the top layer there was a more even split of both types. The variation in the top layer was higher than what we have seen in other theropod species.

As time went on, these findings suggest that the dinosaur was different.

The changes in the femurs of the tyrannosaurus rex are not related to the specimen's sex or age. Gregory Paul, lead author of the paper, says that the changes in the femur may have evolved from a common ancestor who displayed more robust femurs to become more gracile in later species.

The specimen could potentially be considered a separate species because of the differences in robustness across layers.

As a result of their findings, the researchers have now described threemorphotypes.

The team has nominated two new species, one of which is the tyrant emperor lizard, which has more robust femurs and two incisor teeth.

The second, T. regina, had smaller, more gracile femurs and one incisor tooth.

The T. rex was found in the upper and middle layer of the soil, with individuals carrying more robust femurs while only having one incisor tooth.

The authors caution that the differences are not definitive of the new species, and can't completely rule out the possibility of atypical sexual dimorphism due to the small number of samples analyzed.

The team thinks that the location of the fossils in the geologic record points to the existence of two previously unknown species of tyrannosaurus rex.

The revision of these new species is expected to be included in the future, if more specimen are found that fit their framework.

Evolutionary Biology published the study.