As many as 1.7 billion T-rexes once dominated the planet, finds new study

In 2021, paleontologists estimated that up to 2.5 billion T. rexes lived on Earth. A new study, however, has refuted this claim. 
Mrigakshi Dixit
Illustration of dinosaur tyrannosaurus rex on top of mountain.
Illustration of dinosaur tyrannosaurus rex on top of mountain.


How many terrifying Tyrannosaurus rex (T. rex) once roamed the Earth? This question is shrouded in mystery, making it difficult to reach a definitive answer. These massive predators dominated parts of the globe during the Cretaceous period around 68 million years ago. 

In 2021, paleontologists estimated that up to 2.5 billion T. rexes lived on Earth during their entire existence. A new study, however, has refuted this claim. 

The population was relatively smaller than initially predicted in the 2021 study, according to new research led by evolutionary ecologist Eva Griebeler of the Johannes Gutenberg University of Mainz in Germany. 

The number comes down to approximately 1.7 billion T.rex individuals that once lived on this planet. 

The new study builds on previous research led by paleontologists from the University of California (UC), Berkeley. The UC team used a computer model that fed various factors such as average body weight, population density, geographic spread, egg count, average lifespan, and more that led to the prediction of this impressive population number. Altogether, this put the T. rex population at 2.5 billion people.

However, Griebeler suspected some discrepancies in the information fed into the computer simulation in the original study. Griebeler fine-tuned the model with updated data. The new study, for example, suggests that T. rex's survival rates and egg-laying behavior may be similar to that of modern birds and reptiles. And that crucial information may have been overlooked in the original study. 

When this new information entered the computer simulation model, these magnificent beasts' population reached around 1.7 billion. 

Interestingly, according to new current estimates, experts have recovered less than one percent of the T. rex remains compared to its huge population size. With this update, there’s a lot to be learned about this famous dinosaur species.  

This new study has been published in the journal Palaeontology.

Study abstract:

I present a simulation model on vital statistics, absolute abundance (N, total number of individuals that ever lived) and preservation rate (p, minimum number of fossils known divided by N) of Tyrannosaurus rex. It is based on a published age-structured population model that assumes a reptile or bird-like reproduction for T. rex to estimate its age-specific survival rates. My model applies input variables and equations from a recently published model on N and p. This model yielded 2.5 billion T. rex individuals (N) and one fossil per 80 million individuals (p). The average N values calculated by my model were at minimum 27.6% and p values at maximum 361.5% that of a previous model and uncertainties in all output variables were always larger in my model. The equation on output variable ‘population density’ introduced the largest uncertainty to N and p. The output variable ‘generation time’ differed the most between models, but for N and p, the huge size of the input area modelled and geological longevity minimized this difference. 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. Their values also disagreed with those of large extant reptiles, birds and mammals. All of these shortcomings of the previous model favour the assessment of individual and population characteristics of T. rex and of other extinct species using my model.

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