An artist's interpretation of what Tyrannosaurus rex may have looked like. (Image credit: Shutterstock)
LiveScience has a story about how many Tyrannosaurus rex individuals ever lived. Back in April 2021, a paper in the journal Science estimated that 2.5 billion T. rex had existied from 68 to 65 million years ago. Now a new paper by Eva Griebeler, an evolutionary ecologist at the Johannes Gutenberg University of Mainz in Germany, had adjusted that number down by 8 billion to 1.7 billion. She published her analysis in the journal Palaeontology recently. Both models estimate that each T. rex generation included about 20,000 individuals. The big difference was in the number of generations, Griebeler calculated 90,000 generations, while the previous researcher, Charles Marshall, a paleontologist at the University of California, Berkeley, calculated 125,000 generations.
In the original study, Marshall's team created a complex model that factored in a number of different variables — such as average body mass, population density, approximate geographic range, age of sexual maturity, number of eggs laid, average lifespan, survival rates and generation time — to estimate how many T. rex could have survived alongside one another. The model revealed that each T. rex generation likely consisted of around 20,000 individuals and that there were around 125,000 generations in the 2.5 million years they existed — meaning 2.5 billion T. rexes in total.
But Griebeler disagreed with some of the data imputed into this model. She believed Marshall's team overestimated the survival rates and egg-laying capabilities of T. rex, as well as the number of generations that existed during this time, which skewed the results.
Research by Griebeler published shortly after the original study found these values were likely more similar to those seen in modern birds and reptiles. When these values were imputed into an updated model, it revealed that there were 19,000 individuals in each T. rex generation and that there were only around 90,000 generations, meaning the maximum number of T. rex to exist was 1.7 billion.
