Study estimates North America was home to billions of T Rexes over its lifetime

One of the most famous of all the dinosaurs that roamed the ancient Earth is the Tyrannosaurus rex or T Rex. Everyone is familiar with the T Rex making it arguably one of the most famous dinosaur species that ever existed. Many may have never considered how many T Rex dinosaurs lived in what is now North America about 2.5 million years ago.

A new study conducted by scientists at the University of California, Berkeley, estimates that during the Cretaceous Period about 2.5 million years ago, as many as 2.5 billion T Rex dinosaurs lived and died in North America. The research team found that about 20,000 adult T Rex dinosaurs likely lived at any one time, give or take a factor of 10.

2.5 billion T Rex dinosaurs living over the 2.5 million years the creature was one of the dominant predators on the planet is a massive number. The study marks the first time anyone has been able to calculate population numbers for animals that have been extinct for millions of years. The team of researchers is surprised that the number could be calculated at all.

Despite coming up with the number, scientists on the study team point out that there are significant uncertainties in their estimates. They are 95 percent confident that there were likely 20,000 adults at any given time. Within the confidence range, there could have been between 1300 and 328,000 individual animals.

Using that range, researchers say there could have been anywhere from 140 million to 42 billion over the lifetime of the species. Researchers used Monte Carlo computer simulation to figure out how uncertainties in the data translated into uncertainties in the results. Scientists say their calculations depend on something called Damuth's Law, which has to do with body mass versus population density for living mammals. They do admit the uncertainty in the relationship spans about two orders of magnitude.