2.5 billion T. Rexes have roamed the earth, but not all once: study

A Tyrannosaurus rex seems scary enough. Now imagine 2.5 billion. That’s how many of the fierce dinosaur kings likely roamed Earth over the course of a few million years, a new study finds.

Using calculations based on body size, sexual maturity and the creatures’ energy needs, a team from the University of California, Berkeley found out how many T. rex survived more than 127,000 generations, according to a study in the journal Science from Thursday. It is a unique number, but only an estimate with a margin of error the size of a T. rex.

“That’s a lot of jaws,” said lead author Charles Marshall, director of the University of California Museum of Paleontology. ‘That’s a lot of teeth. That’s a lot of claws. “

The species roamed North America for about 1.2 million to 3.6 million years, meaning T. rex’s population density was small at all times. There would be about two in a place the size of Washington, DC, or 3,800 in California, the study said.

“Probably, like many people, I literally took a double shot to make sure my eyes hadn’t deceived me when I first read that 2.5 billion T. rexes ever lived,” said paleobiologist Kristi Curry Rogers of Macalester College who was not part of the study.

Marshall said the estimate helps scientists calculate the conservation rate of T. rex fossils and underscores how lucky the world is to know about them at all. About 100 T. rex fossils have been found – 32 of them with enough material to assume they are adults. If there were 2.5 million T. rex instead of 2.5 billion, we probably never would have known they existed, he said.

Marshall’s team calculated the population using a common biological rule of thumb that says the larger the animal, the less dense the population is. Then they added estimates of how much energy the carnivorous T. rex needed to survive – somewhere between a Komodo dragon and a lion. The more energy required, the less dense the population. They also took into account that the T. rex reached sexual maturity somewhere between 14 and 17 years and lived up to 28 years.

Given the uncertainties in generational length, range, and how long they roamed, the Berkeley team said the total population could be as little as 140 million or as much as 42 billion with 2.4 billion as the middle value.

The science of the largest terrestrial carnivores of all time is important, “but the truth, as I see it, is that things like this are just really cool,” said James Farlow, a professor of geology at Purdue University.