The Iconic Tyrannosaurus Might Actually Be Three Separate Species Of Dinosaurs

By a wide margin, tyrannosaurus rex is the most famous and beloved dinosaur in the world. Dubbed the “King of the Tyrant Lizards”, everything about this ferocious Cretaceous predator seems like it was built to rule, from its muscular body stretching as long as a school bus, from snout to tail, to its skull in plush adorned with 60 serrated teeth, each designed to pierce and grab the flesh of gigantic prey. And like a true king, T. rex ruled his domain alone, being the only species of the genus Tyrannosaurus. Where is it?

A recent analysis of T. rex fossils suggest that the genus may in fact comprise three distinct but closely related species of Tyrannosaurusciting both anatomical and stratigraphic evidence from three dozen specimens discovered around the world.

The main differences identified in the three distinct species proposed are quite subtle but significant. These include the shape of the femur and the configuration of the teeth.

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Distinguishing closely related species can be very difficult, especially those that have been extinct for over 65 million years. Take, for example, a group of South American finches known as “capuchino” seed-eaters. Many of these birds look very similar, apart from a few subtle clues. Male black-throated seedeaters and swamp seedeaters look exactly alike in shape and size except for the color of their plumage. The former has a black throat, while the latter has a white throat. Their songs are also different; one species may have trills in different sections of the song, while another may be buzzy.

Yet plumage color or vocalization cannot be preserved, so closely related dinosaur species can be easily mixed into one. Individual variation due to age and gender adds to the challenge.

Variations in the shape of the femur reported previously and specimens with one or two thin incisors on either side of the front jaw suggested the Tyrannosaurus genre is richer than at first sight. Gregory Paul and his colleagues took over here and compared the sturdiness of the femur in 24 T. rex specimens. They also measured the diameter of the base of the teeth to see if a specimen had one or two thin incisors.

Some specimens had more study femora – calculated using the length and circumference of the thigh bone – while others had more slender femora. The researchers found that the stout femurs were twice as abundant as the slender variety. If these substantial differences were due to gender differences, you would expect a ratio closer to 50/50. Robust femurs have been found in T. rex juveniles while some adult dinosaurs had gracile femurs, which also rules out differences due to age and developmental stages.

When it comes to tooth variation, scientists have found that T. rex specimens with a single incisor tooth were correlated with an often high femoral gracilis.

And, finally, the researchers also analyzed the stratigraphy of each specimen, the classification of the different layers or the stratification of the sedimentary deposits. When a fossil is found in the lower layers of sediment, it means that it is older than those found in the ground higher up. Of the 37 Tyrannosaurus Of the specimens included in this study, 28 have been found in Late Maastrichtian Late formations in North America, which are estimated to be between 67.5 and 66 million years ago.

But only robust Tyrannosaurus femora were found in the lower layer of sediment, which is conducive to robustness variation in other theropod species, indicating that a single species of Tyrannosaurus existed at that time. One Grace Tyrannosaurus femur was identified in the middle layer with five other slender femurs in the top layer, alongside other robust femurs. This suggests that perhaps those specimens found in higher sediment layers developed into more distinct specimens than those found in lower levels.

“We found that changes in Tyrannosaurus the femurs are probably not related to the sex or age of the specimen. We propose that changes in the femur may have evolved over time from a common ancestor that exhibited more robust femora to become more slender in later species. The differences in femur robustness between sediment layers can be considered distinct enough that the specimens could potentially be considered separate species.

The emperor, king and queen lizard

Outraged T. rexresearchers have named two potential new species: Imperator Tyrannosaurus (tyrant lizard emperor) and tyrannosaurus regina (tyrant lizard queen), both aptly named to preserve the royal character of the line. The first concerns specimens found in the lower and middle sedimentary layers, characterized by more robust femurs and two incisors. The second, T. Regina, is related to specimens from the upper and possibly middle layers of sediments, having thin femurs and an incisor tooth. In the meantime, good old T. rex is connected to the upper and possibly middle layer of sediments, with specimens showing a more robust femur while having only one incisor.

As a caveat, the number of specimens is not very large – at least not large enough to make a convincing case of speciation for such subtle morphological differences. After all, the authors themselves cannot exclude that the differences they have highlighted are not due to extreme individual differences. Also, the exact location within the sediment layers is not known for some specimens.

Even so, the mere tangible possibility that T. rex is not alone is fascinating and exciting. Perhaps we will learn more about this royal lineage once more the evidence will surface.

The results are published in the journal evolutionary biology.

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