Were there three distinct species of Tyrannosaurus Rex? • Earth.com
A new study published in the journal evolutionary biology argued that the most iconic dinosaur, Tyrannosaurus Rex, should actually be split into three different species, with T.rex being joined by Tyrannosaurus imperator (“tyrant emperor lizard”) and Tyrannosaurus regina (“tyrant lizard queen”). This proposal sparked a fierce debate in the paleontological community, with many worldwide T.rex experts highly skeptical of the study’s results.
Paleontologists have indeed evoked the notion of multiple Tyrannosaurus species for decades. Due to the vast habitat of this predator, extending over the territory of ancient North America, from western Canada to New Mexico, and given the long period of time (more than one million years) during which the creature had roamed these regions, there was a significant possibility for Tyrannosaurus the populations separate and form several species. Additionally, several differences that paleontologists have identified in extant fossils could also be evidence that more Tyrannosaurus species may have existed, as the authors of the current study argue.
According to a research team led by independent paleontologist Gregory Paul, known Tyrannosaurus fossils vary more than the bones of other large predatory dinosaurs and can be divided into three different groups, based on the robustness of the skeletons and the presence of some chisel- like teeth.
By measuring the femurs and teeth of the lower jaw of 37 Tyrannosaurus skeletons, most of them found in the Hell Creek Formation – a geological formation of Late Cretaceous rocks in North America – Paul and his colleagues showed that the fossils could be divided into three distinct groups: one found in the oldest rock layers, with robust skeletons and two pairs of chisel-shaped teeth (T.imperator), and two found in younger upper layers. Although each of these younger specimens had only one pair of chisel-shaped teeth, one of them had a more robust skeleton (T.rex) and the other a more slender and slender skeleton. (T.regina).
This proposal has already been criticized by several recognized world-renowned paleontologists. For example, according to Jingmai O’Connor – an associate curator of fossil reptiles at Field Museum in Chicago – the femur proportions of the three proposed species overlap rather than show clear separations, as do the periods when dinosaurs were thought to live. For her, this suggests a continuous spectrum of change, which Paul and his team have arbitrarily divided into three species.
“The diagnoses provided for each species are incredibly vague, using words like ‘usually’ and ‘usually’. Even in well-preserved specimens, authors are unable to refer them to a specific species,” said Dr O’Connor.
“I understand the temptation to split the T.rex into different species, because there is some variation in the fossil bones we have. But ultimately, to me, this variation is very minor and does not indicate a meaningful biological separation of distinct species that can be defined on the basis of clear, explicit and consistent differences,” Prof Brusatte said.
Careful investigation of more fossils is needed to settle this debate. Unfortunately, as Paul argues, it could be several decades before there are enough specimens to allow for more scientific statistical analysis.
By Andrei Ionescu, Terre.com Personal editor