The Tyrannosaurus rex is arguably the most iconic of all dinosaurs, immortalized in movie, kids’ toys and crazy Halloween costumes. Its name translates as “king of the tyrant lizards,” and its haunting profile makes it clear why: T. Rex had a huge head, powerful jaws, razor-sharp teeth and a whip-like tail. (Although its puny arms are a comical contrast to the rest of its face.) The T. Rex is believed to have been one of the largest land carnivores of all time, over 40 feet (12 meters) long and 40 feet (12 meters) high at the hips.
But, as with many extinct animals, it’s hard to know how much of a threat the T. Rex was during its reign. (Notably, there has been debate for years as to whether T. Rex was a predator or a scavenger, although recently the scientific consensus leans towards predators.) Were they as common as rabbits, or highly dispersed predators such as snow leopards?
A group of scientists led by Charles R. Marshall, director of the University of California’s Museum of Paleontology, wanted to answer just that. They think they can now roughly estimate how many T. rexes roamed the planet.
Their estimate is roughly 2.5 billion specimens that roamed the Earth together during their existence, which lasted a few million years. (They likely would have lived more generations if not for the extinction event likely triggered by a meteor or comet 66 million years ago.)
The researchers, who published their findings in Science Magazine, estimate that the abundance of T. rexes was about 20,000 individuals in any given period and lived about 127,000 generations. To relate that to the current predator populations, that number of 20,000 is comparable to the current population of African lions, which conservationists estimate at 25,000.
The scientists arrived at their estimate using a wide variety of data. First, they took into account a principle known as Damuth’s law, which states that species with larger body sizes tend to have a lower mean population density. Because this formula includes individuals of a species who had not yet reached their maximum size, the scientists used an estimate for “post-juvenile individuals” – the T. Rex equivalent of a frightened teen. (Now there is a sobering thought.) Once they had that information, they multiplied it by the estimated geographic area where paleontologists believe the monstrous beasts once roamed. They then included what we knew about the time the T. rex lived, although the scientists acknowledge that this figure is particularly unclear ‘because of the poor temporal control over most fossil T. rex sites and because there is a substantial gap in the preservation of dinosaurs among the oldest. T. rex fossils. “
Because experts believe, based on fossil evidence, they lived anywhere from 1.2 million years to 3.6 million years, the team chose the average figure of 2.4 million years. From there, they plugged in other numbers until they finally got to their estimates.
Despite their brief reign of the planet – one that was sadly cut short by the Cretaceous-Triassic Boundary Extinction Event – the fact that another bipedal predator would conduct a count of them 66 million years later speaks to their cultural immortality.
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