Up to 1.7 billion T. rex dinosaurs lived on Earth, a new study finds. But scientists aren’t sure where all the bones have gone.

• New calculations suggest that 1.7 billion T. rex lived on Earth from 65.5 to 68 million years ago.

• Scientists have discovered less than 100 fossilized T. rexes, so there is still more to discover.

• Only a small fraction of dinosaurs are fossilized because it requires the perfect set of conditions.

A new study estimates that 1.7 billion Tyrannosaurus rexes roamed the Earth between 66 million and 68 million years ago, but scientists have recovered fewer than 100.

So the big question is: where are all the dinosaur bones?

This dichotomy between how many T. rexes lived and how few fossils we have of them shows us how rare fossilization is and how much more we need to learn about these majestic creatures.

How scientists count the total population of T. rex

As it turns out, estimating the total number of T. rexes requires complicated calculations, Charles Marshall, a paleontologist at the University of California, Berkeley, told Insider.

And scientists have yet to establish a concrete number.

Marshall was the lead author of a previous study that estimated that 2.5 billion T. rexes once roamed the Earth. That was about 32% higher than the last estimate.

But the new study’s author and evolutionary ecologist at the Johannes Gutenberg University of Mainz, Eva Griebeler, saw an opportunity to improve on the model Marshall and his team had built.

Marshall and his team created a model that took into account several variables, including T. rex population density, mean body mass index, mean lifespan, geographic distribution, age of sexual maturity, number of eggs laid, survival rates, and generation time.

In the new study, Griebeler said she “applied a much more realistic survival curve” to bring the total number of T. rexes down to 1.7 billion.

“It looks like what she’s done is very smart and is a significant advancement beyond the data we’re using in our study,” Marshall said. ‘I have no complaints. It looks like a better set of survival curves than we used.”

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It’s impossible to know exactly how many T. rexes have lived on Earth during their roughly 2 million years, but Marshall’s model and Griebeler’s research provide a reasonable estimate that other scientists can build on.

Where are all the T. rex bones?

Of the approximately 1.7 billion T. rexes that roamed our planet, scientists have discovered only a few hundred fossils, amounting to less than 100 dinosaurs in all.

And only about 30 of them are nearly complete skeletons, George Stanley, a retired paleontologist and professor emeritus at the University of Montana, told Insider.

“If you discover a T-rex tooth during a dig, it’s a big deal to your daily or weekly job,” Stanley said.

Paleontologists are more likely to find fragments of isolated bones, teeth and claws than a perfectly preserved skeleton of a T. rex or any other dinosaur. And even then, finding a fossil is rare.

That’s because the conditions have to be just right in the first place for fossilization to take place.

To become a fossil, an animal’s body must be buried, and in most cases, animal remains are consumed or destroyed by other animals shortly after death, Richard Holtz, a vertebrate paleontologist and associate professor at the University, told me. from Maryland, to Insider.

“Only the tiniest fraction of individuals make it to become a fossil, and only a small fraction of those are discovered,” Holtz said.

And even if the remains are not eaten or taken by other animals, petrification is also highly dependent on the environment.

For example, a dinosaur that lives in the mountains or the open plains is much less likely to become a fossil, because burial in those areas is more difficult than in the lowlands where sediment drains from the mountains, Holtz said.

“Only individuals that lived and died in the right spots are likely to be covered in sand, silt or clay and thus potentially preserved,” Holtz said.

Scientists actually have more T. rex fossils than many other dinosaurs

T. rexes lived in the lowland floodplains with plenty of sediment to bury. That’s why scientists actually have more T. rex fossils and know more about them than many other dinosaurs, Holtz said.

Despite their excellent conditions for fossilization, if Giebeler’s calculations are correct, scientists have found only about 0.0000002% of the T. rex that lived on Earth.

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