The controversial idea that T. rex was three species is criticized

Variation in Tyrannosaurus rex fossils has led some to suggest they are not all the same species

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A controversial claim made earlier this year that tyrannosaurus rex should be divided into three separate species was rejected by another group of researchers.

In March, after analyzing the teeth and leg bones of 38 T. rex fossils, People Scott at the College of Charleston in South Carolina and his colleagues have proposed that rather than there be just one iconic tyrant lizard king”, there were three species.

According to the Persons team, there was a first species, Imperator Tyrannosaurus (tyrant lizard emperor), which later evolved into two more recent species, one of which had a slender build and thin femurs – called tyrannosaurus regina (tyrant lizard queen). The other was more heavily built with sturdy thighs and retained the name T. rex. The team also found variations in the shape of the teeth in the fossilized lower jaws, saying this further supports the idea that T. rex should be considered as three species.

Now a study of James Napoli at the American Museum of Natural History in New York and his colleagues have criticized earlier work. His team found problems with the methods used by the group of Persons to separate the T. rex fossils in groups, based on the measurements of the thigh bones.

By reanalyzing the data with a method that makes fewer assumptions about how the specimens might be divided into groups, the Napoli team found that the fossils clustered together into a single group, rather than separate species.

“I don’t think the data they provided is convincing,” Napoli say. “We found that the specimens simply cluster into a single group, indicating a single species.”

Persons says that while this reanalysis is useful, it’s not superior to the method used by his team. “I think we need to look at all the statistical tests and see what we can learn from the different tests. The method they used is certainly a very safe method – you are very unlikely to make a mistake. But it is very difficult to discover an actual correlation that exists.

The Napoli team also has issues with how Persons’ group measured dinosaur teeth.

“Their measurements for the size of each tooth do not match our measurements for them. And in fact, it seems that in some cases, if that tooth was missing, they measured the size of the tooth socket, which can be misleading,” says Napoli.

“I think it’s really helpful that they’ve restarted this conversation about how many species there are in the fossil record, because we often assume that without testing it very frequently,” Napoli says, but isn’t sure. they did it the right way. .

Persons welcomes the critical response, but stands by its original conclusions. “There are no hard feelings. I think this article does a great job explaining why other scientists would believe T. rex contains only one species,” says Persons. “Taking all the data as a whole, I still stand by our original arguments.”

Other paleontologists say the new study confirms their doubts about the original proposal.

“I disagreed with the original article for many reasons cited in the upcoming article,” says Philip Currie at the University of Alberta in Canada.

“I think the debate is, in fact, resolved – the specimens attributed to T. rex constitute a single species. Now it appears that [Napoli] and his colleagues have rigorously demonstrated this,” says Charles Marshall at the University of California, Berkeley.

However, the case is not entirely closed. More fossils and further analysis of known fossils could be a game changer.

“More specimens are always very useful. And it is possible that some of the T. rex fossils in museums are already in fact of a different species. And we just haven’t noticed the right trait yet,” says Napoli.

“The question of understanding variations in T. rexor any other species, depends on the sample size,” explains Thomas Carr at Carthage College in Wisconsin, one of Napoli’s co-authors. “The kind of evidence we would need to convince me that T. rex is really, say, two species, is to have… a sample size of at least 70 specimens that can be statistically separated into two groups that also have clear and discretely different characteristics from each other, which are seen everywhere [their lives].”

Martin Kundrat at Uppsala University in Sweden thinks it makes more sense to study T. rex as a single species at the moment. “We still don’t have a good understanding of the critical characteristics of this apex predator,” he says, including how characteristics differ between sexes and geographic variability.

Marshall points out that although T. rex were multiple species, it might not be visible in the fossil record. “If we could see them all alive, maybe we would see differences,” he says. “For example, in color or behavior, or aspects not seen in the fossil record, it would make it obvious that there was more than one species. Species designations in paleontology are always tentative.

Journal reference: evolutionary biology, DOI: 10.1007/s11692-022-09573-1

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