The world’s most iconic dinosaur is undergoing an identity crisis.
In February, a team of scientists suggested that Tyrannosaurus rex was actually three different species. Instead of there being just one sovereign “tyrant lizard king,” their paper advocated a royal family of super-sized predators. Joining the king in the genus Tyrannosaurus would be the bulkier and older emperor, T. imperator, and the slimmer queen, T. regina.
The proposed reclassification of T. rex struck the paleontology community as an asteroid and sparked passionate debate. On Monday, another team of paleontologists published the first peer-reviewed counterattack.
“The evidence was inconclusive and had to be answered because the research on T. rex goes way beyond science and into the public sphere,” said Thomas Carr, a paleontologist at Carthage College in Wisconsin and an author of the new rebuttal. . “It would have been unreasonable to let the public think that the multi-species hypothesis was a fact.”
The earlier team of researchers anticipated the rebuttal, which was published in the journal Evolutionary Biology. Gregory Paul, one of the authors of the original study, is working on another paper and says many of the rebuttal’s claims are outlandish.
“I don’t like flat-earthism because the evidence is against it,” said Mr. Paul, an independent researcher and influential paleo artist. “It’s the same here. The evidence is very strong that there are multiple species.”
This king-size taxonomic debate seems destined to rage for ages. Which is not surprising when you consider how difficult it is for researchers to distinguish prehistoric species. Without dinosaur DNA, the lines between one fossil species and another are messy. So paleontologists measure various properties, such as the size and shape of a particular bone. However, the fossils can be misleading, as spending centuries underground can deform the bone. And this is before we consider how sexual differences, injuries, disease and natural variation form bones during the animal’s life.
In living populations, distorted traits are compensated for by large data sets. But the sample size of even known dinosaurs like T. rex is small, according to Philip Currie, a paleontologist at the University of Alberta who didn’t author either study. “The fundamental problem is that while the rough estimate of 100 known specimens of Tyrannosaurus may sound like a lot, it’s not nearly enough,” said Dr. curry.
With paleontologists forced to decipher these fragmented puzzles, the field is littered with mistaken identities and defunct species names. And even the legends aren’t immune — T. rex’s fossil enemy, Triceratops, experienced its own naming drama in 1996 when scientists split the three-horned herbivore into two species.
But perhaps no scientific name is as sacred as Tyrannosaurus rex. Since its name in 1905, the world’s most studied dinosaur has kept its moniker. But Mr. Paul and colleagues’ recent research threatened to send shockwaves through the museum’s galleries by renaming their star attractions.
Several scientists immediately had their doubts. The first study focused on the size of the Tyrannosaurus’ femurs and the existence of two sets of incisors protruding from the predator’s lower jaw.
In the rebuttal study, Dr. Carr that neither trait differs from any of the alleged Tyrannosaurus species. “The characteristics that were claimed to be different between the three species actually overlap,” said Dr. Carr, who published a meticulous study in 2020 examining the properties of more than 40 T. rex specimens. “There was no obvious break between the different strains – we need to have a higher standard than that.” He adds that several well-preserved Tyrannosaurus specimens do not fall into a proposed genus based on their teeth and the hefty size of their femurs.
They are also intended to break through the statistical analyzes used in the original article. According to James Napoli, a paleontologist at the American Museum of Natural History in New York and a co-author of the rebuttal, the statistics used were misleading because the authors defined the number of species they expected before conducting the tests. “It’s a great test if you’re trying to predict which individuals belong to which group and you know how many groups are in your data,” said Dr. Naples. But it’s less convenient to use it to find individual clusters because “it will always group the data into the number of groups you tell it.”
In the original paper, the researchers compared the variation between individual Tyrannosaurus specimens with the variation found between different Allosaurus skeletons. However, the refutation argues that comparing the apex predators is misleading because the Allosaurs come from a single bone bed in Utah, while the Tyrannosaurus fossils come from a scattering of sites over a longer period of time. Therefore, they say that greater amounts of regional and temporal variation in the Tyrannosaurus dataset should be expected.
The rebuttal team also took into account the variability of the living relatives of T. rex – birds. After examining the femurs of 112 species of living birds, the team concluded that the differences between T. rex femurs were relatively inconspicuous.
But Mr. Paul believes that another feature could make this variation more apparent. In an upcoming study, he states that the style of the horns that adorn Tyrannosaurus’ skull is different for each species, such as the contrasting crests that distinguish cassowary species. He says that T. imperator’s horn-encrusted forehead consisted of fusiform cusps, while T. rex’s horns were more knobby. “This should seal the deal,” said Mr Paul.
dr. Naples is not convinced. Like the armor of modern crocodiles, these bony outgrowths were likely encased in keratin, protecting the continuously growing bone beneath. He thinks the shape of a T. rex’s horns probably changed as the animal got older.
The one thing both researchers agree on is the need for more Tyrannosaurus specimens. “As more skeletons are found, they will be added to the dataset, and eventually the statistical support will be so strong that reasonable scientists can’t disagree,” said W. Scott Persons, a paleontologist at the College of Charleston. and a co-author with Mr. Paul on the earlier article.
While neither side is ready to surrender, Peter Makovicky, a paleontologist at the University of Minnesota who was not involved in either study, believes the ongoing back and forth around Tyrannosaurus rex’s identity is good for paleontology. because it allows the public to see the minutiae that define the discipline.
“This gives the layperson insight into why we attach so much importance to distinguishing new species in the fossil record,” said Dr. Makovicky, who counts himself in the camp for one species. “It would be very difficult to convince anyone if it’s a brachiopod, but T. rex takes it to another level.”
