Around 2.5 billion Tyrannosaurus rex dinosaurs existed on Earth, a new study reported Thursday.
It is the first time the total T. rex population over the estimated 2.4-million-year period that the species was on the planet has been calculated.
How scientists calculated the number
A team at the University of California, Berkeley, took into account factors including the size of the dinosaur's geographic range, its body mass, growth pattern, age at sexual maturity and life expectancy. They also estimated the duration of a single generation and the total time that T. rex existed before extinction 66 million years ago.
The team also used a process called Damuth's law linking population to body mass: the bigger the animal, the fewer the individuals that could live at one time.
Some factors proved more difficult to estimate, meaning that the exact number of T. rex's to have lived remains uncertain.
The researchers said the total population could be as little as 140 million or as much as 42 billion. The 2.4 billion figure is a middle value.
The researchers estimated that there were approximately 20,000 adults alive at any one time.
Key T. rex facts
The T. rex was among the largest carnivorous dinosaurs. Its skull measures around 1.5 meters (5 feet) long, with massive and muscular jaws and banana-sized teeth.
According to the new study, the average adult T. rex weighed in at 4717 kilograms (5.2 tons), a male African elephant by comparison weighs between 1,800 and 6,300 kilograms.
Researchers estimate the T. rex had an average lifespan at 28 years and that the species existed on Earth for a total of 125,000 generations.
The dinosaur was spread over around 2.3 million square kilometers (890,000 square miles), with one T. rex roughly every 100 square kilometers.
Paleontologist Charles Marshall, who led the study published in the journal Science, said he hoped the formula used to calculate the number of T. rexs could be applied to other extinct animals in the future.
kmm/rt (Reuters, AP)