As many as 2.5 billion Tyrannosaurus rexes once stalked Earth.
This is the first attempt to calculate total T. rex numbers.
"During the late Cretaceous period, Tyrannosaurus rex prowled Earth in great numbers — in fact, as many as 2.5 billion of these dinosaur kings lived over a period of about 2.5 million years, tramping through North America as they hunted prey and flashed their serrated, banana-size teeth, a new study finds.
Finding this number was no easy feat, according to the researchers. After considering many factors, including the apex predator's population density and home range, they determined that about 20,000 adult T. rex individuals were alive at any one time between about 68 million and 65.5 million years ago, plus or minus a factor of 10, the researchers reported in a study published online Thursday (April 15) in the journal Science.
Of note, the finding includes only post-juvenile T. rex individuals. That's because younger T. rex likely lived in different niches and ate different foods than older individuals did; moreover, they didn't always survive to maturity, and so weren't included in the final tally, the researchers said.
The finding, once thought impossible, is the first calculation for the population of any extinct beast that lived long ago and may open the door to similar calculations for other extinct creatures, the researchers said."
-Ashley Poust, University of California, Berkeley; Daniel Varajão de Latorre, University of California, Berkeley-
