Ever wondered how many Tyrannosaurus rex ever roamed the Earth? The answer is 2.5 billion over the two million or so years for which the species existed, according to a calculation published today in Science1. The figure has allowed researchers to estimate just how exceedingly rare it is for animals to fossilize.
Palaeontologists led by Charles Marshall at the University of California, Berkeley, used a method employed by ecologists studying contemporary creatures to estimate the population density of T. rex during the late Cretaceous period.
“You hold a fossil in your hand and you know it’s rare. The question is, how rare?” says Marshall. “To know that, you need to know how many of them existed.”
To do that, he and his co-authors turned to a method used to estimate the population density of living animals from their body mass and the geographic ranges that they occupy. Damuth’s Law stipulates that the average population density of a species decreases in a predictable way as body mass increases; for example, there are fewer elephants than mice in a given area. [Continue reading…]