The tyrannosaurus rex It is known as one of the greatest predators in history. It lived for approximately one and a half million years, according to the paleontologist and director of the Granada Science Park, Luis Alcala. And probably, it is one of the most recognized extinct animals. Numerous investigations have been made in this regard, such as the speed at which it walked, which was similar to that of humans, or the discovery of new relatives. He has appeared in and starred in numerous blockbusters, including Jurassic Park, and has even given its name to a musical group. Until now it was known as the only species within the genus Tyrannosaurus. However, this Tuesday a research on Evolutionary Biology which raises the possibility that in reality the fossils found of these animals attend three different species and not just one. Even the authors have given names to these potential new species: tyrannosaurus imperator and tyrannosaurus regina. This classification arises after an analysis of physical differences in the femur, other bones and dental structures among the individuals found.
In total, bone and dental remains of 38 specimens were analyzed. In 24 of them, they compared the robustness of the femur, based on its length and circumference, which allows knowing the strength of the bone. The results harbored variety in the femurs with some robust and others graceful. The difference in robustness in some cases was very significant and they even found that there were some twice as robust as graceful. For this reason, they ruled out that it was a difference caused by sex. Furthermore, they suggest that it is not related to growth because robust femurs were found in juvenile specimens and some gracile ones in adults. They also measured the diameter of the base of the teeth or the space in the gums to see if the samples had one or two thin incisor teeth on each side of the front ends of the jaw. Those who have a single incisor tooth correlates with greater gracefulness. Only 12 of all the fossils analyzed had femur measurements and dental remains.
The number of individuals analyzed is a fundamental aspect, according to the paleontologist, professor emeritus at the Autonomous University of Madrid and member of the Royal Academy of Exact, Physical and Natural Sciences, Jose Luis Sanz: “This number is not enough to be statistically significant. At the moment I would not dare to put a name and say that they are different species until we have a greater number of specimens”. Alcalá, for his part, agrees with the prematureness of having appointed them and defends that, although they may be right, the evidence they have given to argue it is “very weak”.
The tyrannosaurus imperator it has been related to remains found in the lower and middle layers of the sediment. They are characterized by more robust femurs and usually two front teeth. This could be due, as they defend, to the fact that they have preserved it from their ancestors. tyrannosaurus regina, for its part, is related to remains from the upper and, probably, middle layers of the sediment, with thinner and, therefore, more graceful femurs, and a single incisor tooth. the already known tyrannosaurus rex it was identified in the upper layer and possibly in the middle of the sediment, with specimens with more robust femurs and one incisor tooth. Gregory Paulindependent researcher, and illustrator who has helped establish the look of Mesozoic creatures in documentaries and films such as Jurassic Park and one of the authors of the research, defends that only a quarter of the specimens found correspond to this species.
The investigation, he says, arose after a talk in 2010 by the Vertebrate Paleontology Society, in which John Scannella spoke about triceratops, one of the prey of the Tyrannosaurus. At that time it was considered whether, like these, this predator would have developed new species. In addition, he wanted to provoke a taxonomic investigation on this dinosaur, since he considered that it was forming a kind of “garbage” in which the specimens were thrown into Tyrannosaurus t-rex without first performing an anatomical and stratigraphic analysis. Paul argues that the fossils found indicate that t rex it was not a single species that remained the same, but rather evolved according to Darwinian theory. These animals lived during the Cretaceous, which ended 66 million years ago.
The authors do not rule out that the observed variation is due to atypical sexual dimorphism or extreme individual differences, but argue that the variability in robustness is much more extensive than that observed in large dinosaur species. Sanz emphasizes that it is “much appreciated” that at the end of the investigation there is a table with arguments for and against the investigation. “The only thing is that I think some of those problems, like the small sample size, is one of the main ones, as they themselves admit,” he says.
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