For the first time, scientists have estimated how many Tyrannosaurus rex, the so-called king of dinosaurs, once traveled on Earth.
Why does it matter: The number is staggering: 2.5 billion Tyrannosaurus rex lived and died in 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 fossil records and the rarity of finding certain fossilized prehistoric organisms, according to lead researcher Charles Marshall, director of the University of California’s Museum of Paleontology.
- “I mean, for me, it’s just amazing that we could have come up with 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 in?’ The answer is no, because they did not exist. “
How it works: The team of researchers could not use limited fossil records to estimate the species’ population, 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 then calculated the average body weight of a T. rex, averaging 5,200 kilograms (about 11,460 pounds).
- Using body mass and population density, the team calculated that the species had a population density of about one individual per 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 have traveled on Earth, the team multiplied the permanent population of the species by the number of generations it has traveled (approximately 127,000), which they determined by dividing how long the species survived at its estimated generation time. 19 years.
- The researchers noted that the estimated population density for the species would translate to about 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 was primarily 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 used by the team.
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 missing animals.
- “It’s an exercise in what you can and can’t say,” Clark said. “It gives you a chance to say, ‘Wow, there really were a lot of these things, and we don’t get a lot of them recorded in fossils.’
Go deeper: How the meteorite that killed the dinosaurs created modern forests