For the first time, scientists have estimated how many Tyrannosaurus rex, the so-called king of dinosaurs, once traveled the Earth.
Why it’s important: The figure is staggering: 2.5 billion rex tyrannosaurs lived and died during the roughly 2.4 million years the species survived on the planet, according to a new study published in the journal Science Friday.
The study may help contextualize the fossil record and the rarity of finding certain fossilized prehistoric organisms, according to principal investigator Charles Marshall, director of the University of California’s Museum of Paleontology.
- “I mean, for me, it’s amazing that we were able to reach a number,” Marshall told Axios. “Some people have asked me,‘ How does your number compare to other numbers out of the total you’ve ever lived? “The answer is no, because there was none.”
How it works: The team of researchers could not use the limited fossil record to estimate the population of the species, so they used Damuth’s Law, which describes a relationship between population density and body mass.
- The relationship, used in population ecology, generally states that species with larger body sizes tend to have lower population densities.
- The researchers calculated the average body mass of a T. rex, averaging 5,200 kilograms (approximately 11,460 pounds).
- Using body mass and population density, the team calculated that the species had a population density of about one individual for every 40 square miles.
By numbers: With this information and an estimated geographical area occupied by the species, the researchers were able to estimate that approximately 20,000 T. rex were alive at a time when the species lived on the planet.
- To find the total number of T. rex that traveled the Earth, the team multiplied the permanent population of the species by the number of generations it covered (about 127,000), which they determined by dividing the time it survived. the species for the estimated generation time of 19 years.
- The researchers noted that their estimated population density for the species would translate to approximately 3,800 T. rex in an area the size of California and only two in an area the size of Washington, DC.
Yes, but: Marshall said the accuracy of the analysis was “low” and this is mainly due to uncertainty about the accuracy of the relationship between the body mass of live animals and their population density, rather than the paleontological data that goes use the equipment.
James Clark, a biology professor at George Washington University who did not participate in the study, said the research did not reach a definitive conclusion, but showed difficulties in estimating the lives of extinct animals.
- “It’s an exercise of what can and can’t be known,” Clark said. “It gives you a chance to say, ‘Wow, there really were a lot of these things, and we don’t take them to the fossil record.’
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