2.5 billion T. Rexes wandered on earth, but not all: Study

One Tyrannosaurus rex looks scary enough. Now imagine 2.5 billion of them. That’s how much of the fierce dinosaur king probably roamed the earth over the course of a few million years, a new study finds.

According to a study in the journal Science, Thursday, a team at the University of California, calculations based on body size, sexual maturity and the energy needs of the creatures, determined how many T. rex lived more than 127,000 generations. This is a first number of its kind, but only an estimate with an error margin the size of a T. rex.

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

The species roamed North America for about 1.2 million to 3.6 million years, meaning the T. rex population density was small at any given time. There would be about two in a place as big as Washington, DC or 3,800 in California, the study said.

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

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

The Marshall team calculated the population using a general rule of biology that says the larger the animal, the smaller its population. Then they added estimates of how much energy the carnivorous T. rex needed to stay alive – somewhere between a Komodo dragon and a lion. The more energy needed, the less dense the population. They also kept in mind that the T. rex reached sexual maturity between 14 and 17 years of age and lived at most 28 years.

Given uncertainty about the creature’s generation’s length, size and how long they migrated, the Berkeley team said the total population could be as low as 140 million or as much as 42 billion, with 2.4 billion as the mean.

The science of the greatest terrestrial carnivores of all time is important, “but the truth, as I see it, is that these kinds of things are just very cool,” said James Farlow, professor of geology at Purdue University.