The famous T. rex has been re-crowned as the one-and-only 'king of the dinosaurs' after scientists dismissed claims the legendary beast was three separate species.
The fearsome Tyrannosaurus rex is the deadliest land animal to have roamed the Earth - reaching 40 feet long, 12 feet tall and weighing over eight tons.
Its razor-sharp teeth chomped down with a seven-ton force.
In February paleontologists controversially called for T. rex to also include T. imperator meaning "tyrant lizard emperor" and T. regina - Latin for "tyrant lizard queen."
It was based on an analysis of the leg bones and teeth of 38 T. rex specimens, including 'Sue', a complete Tyrannosaurus skeleton on display in Chicago.
Now Professor Steve Brusatte and his colleagues have offered a rebuttal - finding "insufficient evidence" for the iconic creature's reclassification.
Professor Brusatte, a paleontologist at Edinburgh University and co-author of the study, said: "Tyrannosaurus rex remains the one true king of the dinosaurs.
"Recently, a bold theory was announced to much fanfare: what we call T. rex was actually multiple species.
"It is true that the fossils we have are somewhat variable in size and shape, but as we show in our new study, that variation is minor and cannot be used to neatly separate the fossils into easily defined clusters.
"Based on all the fossil evidence we currently have, T. rex stands alone as the single giant apex predator from the end of the Age of Dinosaurs in North America."
The team re-analyzed the data and also looked at 112 species of bird descendants and four non-avian theropod dinosaurs.
The multiple species argument was found to be based on a limited comparative sample, non-comparable measurements and improper statistical techniques.
"But this claim was based on a very small comparative sample. When compared to data from hundreds of living birds, we actually found T. rex is less variable than most 'living theropod dinosaurs'. This line of evidence for proposed multiple species doesn't hold up."
Mr. Paul and colleagues noted physical differences in the thigh bone - as well as dental structures and bones.
They suggested the larger specimens should be attributed to Tyrannosaurus imperator and smaller ones to Tyrannosaurus regina.
"Our study shows that rigorous statistical analyses that are grounded in our knowledge of living animals is the best way to clarify the boundaries of extinct species.
"In practical terms, the three-species model is so poorly defined that many excellent specimens can't be identified. That's a clear warning sign of a hypothesis that doesn't map onto the real world."
The international team could not replicate the earlier tooth findings - and recovered different results from their own measurements of the same specimens.
In addition, they took issue with how the 'breakpoints' for each species using these traits were statistically determined.
The statistical analysis in the original study defined the number of groups before the test was run - so is not useful for testing the hypothesis.
They used a different statistical technique to determine how many clusters exist within the data without any advanced assumptions.
They found they are best considered as a single group or one species - i n other words, T. rex.
Co-author Prof Thomas Holtz, from the University of Maryland, said: "The boundaries of even living species are very hard to define: for instance, zoologists disagree over the number of living species of giraffe.
"It becomes much more difficult when the species involved are ancient and only known from a fairly small number of specimens.
"Other sources of variation - changes with growth, with region, with sex, and with good old-fashioned individual differences - have to be rejected before one accepts the hypothesis that two sets of specimens are in fact separate species. In our view, that hypothesis is not yet the best explanation."
To date, Tyrannosaurus rex, or the 'tyrant lizard king', is the only recognised species in the group of dinosaurs, or genus, known as Tyrannosaurus.
Co-author Dr. David Hone, of Queen Mary University of London, said: "T. rex is an iconic species and an incredibly important one for both paleontological research and communicating to the public about science, so it’s important that we get this right.
"There's still a good chance that there is more than one species of Tyrannosaurus out there - but we need strong evidence to make that kind of decision."
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