The Tyrannosaurus rex is dinosaur royalty, an iconic and instantly identifiable species – and according to a new study, as many as 1.7 billion of these beasts roamed Earth before an unfortunate meeting with an asteroid.
It takes a lot of number crunching to figure this out, everything from average lifespan to sexual maturity to the number of T. rex eggs that survived has to be calculated and factored in to reach an estimate.
While 1.7 billion is undoubtedly a large figure, it’s some 800 million dinosaurs fewer than the estimate reached by a 2021 study. The latest analysis is based on the most up-to-date information we have on dinosaur growth and reproduction, and it looks to be the more accurate one.
“Unlike my model, 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,” writes evolutionary ecologist Eva Griebeler from the Johannes Gutenberg University of Mainz in Germany.
“Their values also disagreed with those of large extant reptiles, birds, and mammals. All of these shortcomings of the previous model favor the assessment of individual and population characteristics of T. rex and of other extinct species using my model.”
Before we’re too critical of the previous estimate, it’s worth remembering that it was the first of its kind and still contains plenty of valuable data. However, this new research used updated models of T. rex survival and maturity rates.
Put simply, the new calculations suggest a lower T. rex survival rate, fewer generations in total, and a reduced amount of egg-laying. We have pretty decent data on these factors based on detailed fossil studies and comparisons with modern-day species that scientists think have kept certain dinosaur traits.
Griebeler tested her model against data on 23 different extant species among reptiles, birds, and mammals and found that it predicted population numbers pretty well compared to the previous model. That suggests it should work for the Tyrannosaurus rex too.
The good news is that one of the authors behind the 2021 estimate, University of California, Berkeley, paleontologist Charles Marshall, approves of the new work: he told Live Science that the latest figure was “more realistic”.
As well as reaching that hefty 1.7 billion number, the research also suggests that we’ve found a minuscule percentage of the T. rex remains. Why that percentage is so small – and where all the other bones are – is a question for future study.
Griebeler suggests that her model – which focuses on maximum lifespan, sexual maturation age, and maximum annual offspring numbers – can also help estimate population numbers for other extinct species.
“All of these shortcomings of the previous model favor the assessment of individual and population characteristics of T. rex and other extinct species using my model,” writes Griebeler.
The research has been published in Palaeontology.