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Billions, Yes, Billions of T. Rexes Have Once Roamed The Earth

There have been billions of T. rexes on Earth over the 2.5 million years dinosaurs lived on our planet.

Billions, Yes, Billions of T. Rexes Have Once Roamed The Earth
Illustration of T. rexes ALLVISIONN/iStock

Imagine a world where Tyrannosaurus rexes (T. rexes) roamed the Earth, gnashing their sharp teeth at any tasty prey, and ruling the roost. Now imagine a world where 2.5 billion of these dinosaurs lived. 

A team of paleontologists at UC Berkeley dug for answers to their question: "How many Tyrannosaurus rexes roamed North America during the Cretaceous period?"

It turns out, a rather large amount did. 

The team found out that at any one time, roughly 20,000 adult T. rexes were most likely roaming these North American lands. By putting two and two together, the team concluded that this means approximately 2.5 billion T. rexes were alive during their two and a half million years on Earth.

This marks the first time scientists compute these numbers in this way. However, their conclusion does come with quite a vast range of figures. 

As Charles Marshall, professor at UC Berkeley and lead author of the study, which was published in the journal Science, noted, the number of T. rexes could vary anywhere from 140 million to 42 billion. 

The issue lies in the number of available fossils. 

How the team computed the numbers

Marshall and his team fed the numbers into computer simulations to minimize the huge variation in figures. And as Marshall pointed out, "Ecological differences result in large variations in population densities for animals with the same physiology and ecological niche." 

"Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship spans about two orders of magnitude," he said.

Hence the wide number range of potential T. rexes roaming Earth. 

Ultimately, the team's best guess lies at 2.5 billion total T. rexes — which is pretty impressive in itself. 

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As Marshall said, "In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it."

And the possibilities of finding out more about T. rexes, and other dinosaurs, keep increasing as more fossils get discovered, and the technology to study them improves.

"Our knowledge of T. rex has expanded so greatly in the past few decades thanks to more fossils, more ways of analyzing them, and better ways of integrating information over the multiple fossils known."

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