“How many Tyrannosaurus rex were there?” It’s a question that’s been answered before, but a study published last month offers up a new figure, challenging previous assumptions.

From the dawn of the dinosaurs until their extinction, 1.7 billion of the thin-lipped, intimidatingly clever, and surprisingly slow theropods roamed the Earth, according to the new and improved calculations.

A previous study from 2021 put the all-time total number of “tyrant lizards” at 2.5 billion, but this most recent paper, published almost exactly two years to the day later, suggests there may actually have been far fewer.

The latest estimate is by no means measly – 1.7 billion is still a lot of dinosaurs, after all. But what happened to those other 800 million?

The new model, created by Eva Griebeler, an evolutionary ecologist at the Johannes Gutenberg University Mainz, attempts to address some of the “shortcomings” of the original study, and as a result, has turned out a much smaller figure.

“Unlike my model,” Griebeler writes, “the generation time as well as life expectancies, gross reproduction rates, and reproductive values of individuals calculated from the previous model all strongly contradicted our current understanding of the biology of T. rex and of other theropods."

"Their values also disagreed with those of large extant reptiles, birds and mammals.”

Taking all this into consideration, Griebeler created an updated model, which calculated that T. rex were T.rex-ing for roughly 90,000 generations, each of which had around 19,000 individuals. Tallying this up gives the maximum number of T. rex as 1.7 billion.

The previous model, on the other hand, estimated there to be a total of 127,000 generations of T. rex, each with approximately 20,000 individuals.

Fortunately, it seems there is no bad blood between the authors of the two studies: Charles Marshall, lead author of the 2021 paper, conceded that Griebeler’s is a "more realistic" estimate, Live Science reports.

Either way, 1.7 or 2.5 billion, there’s still a huge number of T. rex missing from the fossil record. If Griebeler’s model is correct, then only one fossil has been recovered per 52.5 million individuals, begging the question: Where are they?

It’s just one of the many mysteries surrounding arguably the most famous of the dinosaurs, about whom we are still learning so much.

The study is published in Palaeontology.

[H/T: Live Science]