The tyrannosaur war continues. A few months after a team of American researchers proposed that Tyrannosaurus rex, the most famous dinosaur of all time, actually corresponded to three different species, other paleontologists decided to publish a detailed challenge to this hypothesis.
According to them, the idea may even be interesting on paper, but the arguments used to defend it don’t make much sense.
The new study, signed by a team from the USA and coordinated by Thomas Carr, from Carthage College, has just appeared in the specialized journal Evolutionary Biology, the same journal that housed the original research on the supposed trio of tyrannosaurs.
Supporters of the idea, such as independent researcher Gregory Paul, claim to see considerable variability in the levels of robustness and dentition of superpredator fossils, which would be enough to propose that we are facing three species, not just one. Also, the critters would have lived at slightly different times at the end of the Age of Dinosaurs. According to Paul and company, it would be correct to consider the following division:
- An older and more robust species, the T. imperatorwhich had two incisors (teeth equivalent to the incisors of mammals like us);
- Two more recent species whose dentition included only one incisiform. The strongest would be T. rex itself, while the more graceful (that is, with the slenderest bones) would receive the name of T. regina.
The scientific names come from the Latin words for “emperor”, “king” and “queen”, respectively. When the work was published in March 2022, Paul told Sheet that the difference between species could be linked, for example, to slightly different ecological niches.
Although all were large predators, the more robust animals would have specialized in hunting the mighty Triceratops, the herbivore that resembled a rhino on steroids. already the T. regina could hunt edmontosaurs, duck-billed plant eaters and without the armaments of the Triceratops.
Even at the time of publication of the first study, however, many people doubted the idea, and the new research details the reason for this skepticism. And the list of reasons is long, starting with a fact pointed out by paleontologists such as the Brazilian Rafael Delcourt, from USP in Ribeirão Preto (who was not linked to any of the studies): the comparison basically focused on the robustness of the femur (the bone thigh) and dentition, which would be little to determine differences between species.
Carr and his colleagues also point out that the temporal difference between the specimens is not clearly defined, since the stratigraphy (basically the succession of rock layers in the paleontological sites) of the sites with fossils of T. rex does not have accurate estimates of dates.
The most serious blow to the three-species idea, however, has perhaps to do with the proposal that “stout” and “graceful” forms of tyrannosaurs existed. This separation was made from an index that basically divided the femur length of each fossil by the diameter of the bone (so seeing which tyrannosaurs had the “chubby” femurs).
In the new study, the researchers performed the same calculations with 112 species of modern birds (which, at heart, are nothing more than carnivorous dinosaurs, related to tyrannosaurs) and four meat-eating dinosaurs. Result: the variation in “robustness” of tyrannosaurs is in the average of birds of the same species today. It would not make sense, therefore, to separate the specimens into different species.
Finally, Carr and company point out that not even the criteria used by the original study would be sufficient to classify most of the analyzed specimens as belonging to one of the three supposed species. With that level of uncertainty, classification would no longer be useful, they argue.
For them, it is more likely that the variability of specimens of T. rex is due to individual differences, linked to age or diet, or even to some form of sexual dimorphism (variation between males and females).
The debate is unlikely to end now, however. Gregory Paul has already announced that he will publish a new study using the ornamentation and bumps on the skulls of the specimens as an argument in favor of the three-species hypothesis.
