For the first time, scientists have estimated how many Tyrannosaurus rex, the so-called king of the dinosaurs, once roamed Earth.
Why it matters: The number is astonishing: 2.5 billion Tyrannosaurus rex lived and died during the approximately 2.4 million years the species survived on the planet, according to a new study to be published in the journal. Science on Friday.
The study According to lead researcher Charles Marshall, director of the University of California Museum of Paleontology, the fossil record and rarity of finding certain fossilized prehistoric organisms can help contextualize.
- “I mean, it’s just amazing to me that we could have come up with a song,” Marshall said to Axios. “Some people have asked me, ‘How does your number compare to other numbers of the total that ever lived?’ The answer is not, because there were none. “
How it works: The team of researchers couldn’t use the limited fossil record to estimate the population of the species, so they used Damuth’s law instead, which describes a relationship between population density and body weight.
- The relationship, used in population ecology, generally states that species with larger body sizes tend to have a lower population density.
- The researchers then calculated the average body weight of a T. rex and found an average of 5,200 kilograms (about 11,460 pounds).
- Using body weight and population density, the team calculated that the species had a population density of about one person per 40 square miles.
In numbers: With this information and an estimated geographic area the species occupied, the researchers were able to estimate that about 20,000 T. rex were alive at any one time the species lived on the planet.
- To find the total number of T. rex roaming Earth, the team multiplied the species’ standing population by the number of generations it spanned (approximately 127,000), which they determined by dividing how long the species survived by its estimated generation time aged 19.
- The researchers noted that their estimated population density for the species would translate to about 3,800 T. rex in an area the size of California and just two in an area the size of Washington, DC.
Yes but: Marshall said the precision of the analysis was “low” and that this was mainly due to uncertainty about the accuracy of the relationship between the body weight of live animals and their population density, rather than the paleontological data the team used.
James Clark, a professor of biology at George Washington University who did not participate in the study, said the study did not reach a definitive conclusion, but showed how difficult it is to estimate the lives of extinct animals.
- “It’s an exercise in what you can and can’t see,” said Clark. “It gives you a chance to say, ‘Wow, there were really a lot of these things, and we don’t get many of them recorded in the fossil record.’ ”
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