Around 2.5 billion Tyrannosaurus rex ever walked the Earth

A total of 2.5 billion Tyrannosaurus rex probably existed during the lifespan of the species, researchers have calculated – suggesting that very few survived as fossils.

Charles Marshall at the University of California, Berkeley, and his colleagues used body mass and population density to estimate how many T. rex once lived.

Larger animals tend to have a larger individual range, because they need more food to support their body mass than smaller animals, meaning body mass is inversely correlated with population density – a rule known as Damuth’s law.

Previous analysis of T. rex fossils shows that the average body mass of an adult was about 5200 kilograms. The team also used climate models and the locations of T. rex remains to estimate that the total geographic range of the species was about 2.3 million square kilometres across North America.

Using these figures and data from living species, the team estimated that there was around one T. rex for every 100 square kilometres in North America. “This would mean there was about 20,000 adult T. rex at any given time,” says Marshall.

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