• The Tyrannosaurus rex was around for 2.5 million years before the dinosaurs went extinct.
• A new study suggests that a total of 2.5 billion adult T. rexes lived and died during that period.
• Paleontologists arrived at the figure by calculating the T. rex life span and population density.
• See more stories on Insider’s business page.

An adult Tyrannosaurus rex required a lot of space — and the prey therein — to survive.

According to new calculations from paleontologists the University of California, Berkeley, each adult T. rex lived in an area roughly 40 square miles in size.

The study, published Thursday in the journal Science, uses that math to offer an estimate of the total number of these predators that walked the Earth during the Cretaceous Period, between 66 and 68 million years ago: an impressive 2.5 billion.

“The total number did catch me off guard,” Charles Marshall, a paleontologist at Berkeley who co-authored the study, told Insider.

Marshall’s analysis suggests that the entire island of Manhattan or city of San Francisco would be the territory of a single T. rex.

He said he’d been wondering for years how unusual it really is to find a T. rex fossil: “When I hold a fossil in my hand, I always said to myself, ‘I know this is freakishly rare.’ But just how rare is it — one in a million or one in a trillion?”

## Comparing the T. rex to the Komodo dragon

The T. rex was one of the largest carnivorous land animals that ever walked the Earth. (That accolade currently goes to the polar bear.) An adult Tyrannosaurus rex could weigh at least 5 tons. It stood about 12 to 13 feet tall at the hip and was about 40 to 43 feet long.

The larger predators are, the fewer of them can live in the same area, since there just isn’t enough food to sustain their massive size. This is known as Durham’s Law. So if researchers know how many calories a meat-eater needs to survive, they can calculate the number of predators per square mile.

While there’s no living predator that resembles the T. rex in size, Marshall compared the dinosaur’s energy needs to those of a Komodo dragon, the largest lizard on Earth.