The world’s most famous dinosaur is going through an identity crisis.
In February, a team of scientists said that Tyrannosaurus rex was actually three separate species. Instead of just being an independent “tyrannical lizard king”, theirs Paper Made the case for a royal family of big game hunters. Joining the king in the Tyrannosaurus genus would be the large and old emperor, T. imperator, and the slender queen, T. regina.
The proposed T. rex reclassification hit the paleontology community like an asteroid, sparking heated debate. On Monday, another team of biologists published a peer-reviewed counterattack.
“The evidence was not convincing and had to be answered because T. rex research is so far beyond science and the public realm,” said Thomas Carr, a biologist at Carthage College in Wisconsin and author of the new rebuttal. “It would have been unreasonable to leave the public thinking that the multiple species hypothesis was true.”
An earlier team of researchers predicted the rebuttal, 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 claims are extraordinary.
“I don’t like Flat Earthism because the evidence is against it,” said Mr. Paul, an independent researcher and influential paleoartist. “It’s the same here: the evidence very strongly indicates that there are multiple species.”
It looks like this king-size taxonomic debate will rage for positions. It is surprising how difficult it is for researchers to distinguish prehistoric species. Without dino DNA, the lines between one fossil species and another are blurred. So biologists measure various traits, such as the size and shape of a particular bone. Fossils can be misleading, however, because wear and tear buried underground can distort the bone. And that’s before considering how sex differences, injuries, disease, and natural variation shape bones during an animal’s life.
In living populations, skewed traits are balanced by large data sets. But specimens of known dinosaurs like T-Rex are smaller, according to University of Alberta paleontologist Philip Currie, who was not an author of either study. “The main problem is that although the estimate of 100 known specimens of Tyrannosaurus may sound high, it is not enough,” said Dr Currie.
As biologists are forced to decipher these fragmented puzzles, the field is littered with misidentifications and defunct species names. And even the legends aren’t immune to it – the T. rex fossil, Triceratops, experienced its own. Naming the drama in 1996 When scientists divided the three-horned herb into two species.
But perhaps no scientific name is as sacred as Tyrannosaurus rex. Since it was named in 1905, the world’s most studied dinosaur has retained its moniker. But a recent study by Mr. Paul and colleagues threatens to send shockwaves through museum halls by rebranding their star attractions.
Many scientists immediately expressed their doubts. Early studies focused on the large tyrannosaurus femurs and the presence of two sets of teeth protruding from the predator’s lower jaw.
In a rebuttal study, Dr. Carr claims that neither trait is unique to any species of tyrannosaurus. “Characteristics that were claimed to be different between the three species were actually overlapping,” Dr Carr said. Complex study examining traits in over 40 T. rex specimens In 2020 “There wasn’t a clean break between different species – we have to get a higher standard out of it.” He added that many well-preserved Tyrannosaurus specimens fail to fall into any proposed species based on their teeth and the height of their femurs.
They also aim to puncture the statistical analyzes used in the original paper. According to James Napoli, a biologist at the American Museum of Natural History in New York and co-author of the rebuttal, the statistics used were misleading because the authors specified the number of species they expected before running the tests. “If you’re trying to predict which individuals belong to which group and you know how many groups there are in your data,” Dr. Napoli said. But using it to find distinct clusters is less useful because “it will always group the data into the number of groups you specify.”
In the original paper, the researchers compared the variation between individual Tyrannosaurus specimens to the variation found between several Allosaurus skeletons. However, the rebuttal claims that comparing apex predators is misleading because allosaurus comes from a single bone bed in Utah while tyrannosaurus fossils come from a scattering of sites over a long period of time. Hence, he says, the high amount of regional and temporal variation in the tyrannosaurus data set should be expected.
The debunking team also looked at the evolution of T. rex’s living relatives – birds. After examining the femurs of 112 living bird species, the team determined that the differences between T. rex femurs were relatively unremarkable.
But Mr. Paul believes that another feature may further explain the variation. In a subsequent study, he noted that the pattern of horns adorning the tyrannosaurus skull differed from species to species, just as contrasting crests distinguish cassowary species. He says that T. imperator’s horned eyebrows consisted of spindle-shaped nodules, while T. rex’s horns were knobby. “That should seal the deal,” Mr. Paul said.
Dr. Napoli is not convinced. Like the armor of modern crocodiles, these bony outgrowths were likely encased in keratin, which protected the ever-growing bone beneath. He believes that the shape of the T. Rex’s horns probably changed with the animal’s age.
One thing both sets of researchers agree on is the need for more Tyrannosaurus specimens. “As more skeletons are found, they are added to the data set and eventually, one way or another, the statistical support will be so strong that a reasonable scientist would Can’t agree,” said biologist W. Scott Persons of the College of Charleston. and a co-author with Mr. Paul on the former paper.
While neither side is ready to surrender, Peter Makowiecki, a paleontologist at the University of Minnesota who was not involved in either study, believes that the constant back-and-forth surrounding the identity of Tyrannosaurus rex is good for paleontology. Because it allows the public to experiment. The minutia that defines the discipline.
“It gives the layman insight into why we care so much about distinguishing new species in the fossil record,” said Dr Makowicki, who counts herself in the single-species camp. “It would be very difficult to convince anyone of this if it were a brachiopod, but the T-rex takes it to another level.”