Clickbait title. It's about walking speed which does not tell us about the running speed.
The article itself cites researchers saying: "the study authors want to incorporate their flexible tail into models of a running T. rex, van Bijlert said. Maximum running speed for a T. rex is thought to be in the range of 10 to 25 mph (16 to 40 km/h), according to Hutchinson."
You could outwalk it if does not run, because this here was about walking speed.
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As for T. rex's next steps, the study authors want to incorporate their flexible tail into models of a running T. rex, van Bijlert said. Maximum running speed for a T. rex is thought to be in the range of 10 to 25 mph (16 to 40 km/h), according to Hutchinson. Biomechanics researchers have long proposed that T. rex's maximum running speed would be limited by the strength of its bones, because the animal was so heavy. However, a flexible tail could change that by acting as a shock damper during running, "allowing it to run faster without breaking its bones," van Bijlert said.
Holtz looks at the hypothesis that juveniles and sub-adults filled the niches that medium-size predators occupied in ecosystems with no tyrannosaurids. If so they'd have needed to have been fast enough to catch smaller prey.
Oh, wow... I followed the link to the other article where they describe how they came up with such a figure:
> “For instance, the T. rex population was likely about 20,000 at any one time, but the 95% confidence range — the range of numbers in which there's a 95% chance the true number falls — is 1,300 to 328,000. In other words, when the T. rex total is calculated (which includes population density, population size at any one time, generation time and total number of generations), the number of T. rex individuals that ever lived could be anywhere from 140 million to 42 billion, the researchers said.”
If you click through that sentence to the linked article [1], you'll discover that it's a pretty misleading one. The 2.5 billion estimate is the total estimated number of adult Tyrannosaurs that lived during a 2.5 million year period (68-65.5 million years ago).
The estimated maximum population of living adult Tyrannosaurs at any one time, on the other hand, is ~20,000, with a 95% confidence interval from 1,300 to 328,000, according to that article.
The article itself cites researchers saying: "the study authors want to incorporate their flexible tail into models of a running T. rex, van Bijlert said. Maximum running speed for a T. rex is thought to be in the range of 10 to 25 mph (16 to 40 km/h), according to Hutchinson."