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Get a daily digest of the most important stories affecting your hometown with Axios Tampa Bay Enter your email address[ ] Please enter a valid email. Please enter a valid email. Subscription failed Subscribe for free Thank you for subscribing! Want a daily digest of the top Charlotte news? Get a daily digest of the most important stories affecting your hometown with Axios Charlotte Enter your email address[ ] Please enter a valid email. Please enter a valid email. Subscription failed Subscribe for free Thank you for subscribing! Enter your email address[ ] Please enter a valid email. Please enter a valid email. Subscription failed Subscribe for free Thank you for subscribing! 5 hours ago - Science 2.5 billion T. rex inhabited the planet, researchers say Jacob Knutson A person cleaning a replica of a Tyrannosaurus rex skeleton at a museum in Newcastle upon Tyne, England, in 2020. Photo: Owen Humphreys/PA Images via Getty Images For the first time, scientists have estimated how many Tyrannosaurus rex, the so-called king of dinosaurs, once roamed the Earth. Why it matters: The number is staggering: 2.5 billion Tyrannosaurus rex lived and died during the roughly 2.4 million years the species survived on the planet, according to a new study set to be published in the journal Science on Friday. The study may help contextualize the fossil record and the rarity of finding certain fossilized prehistoric organisms, according to lead researcher Charles Marshall, director of the University of California Museum of Paleontology. * "I mean, to me, it's just amazing we could have come up with a number," Marshall told Axios. "Some people have asked me, 'How does your number compare to other numbers of the total that have ever lived?' The answer is it doesn't because there weren't any." How it works: The team of researchers couldn't use the limited fossil record to estimate the species' population, so they instead 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 computed the average body mass of a T. rex, settling on a mean of 5,200 kilograms (roughly 11,460 pounds). * Using the body mass, the team calculated that the species had a population density of around one individual per 40 square miles. By the numbers: With this information and an estimated geographic area that the species occupied, the researchers were able to approximate that about 20,000 T. rex were alive at any given time that the species lived on the planet. * To find the total number of T. rex that walked the Earth, the team multiplied the species' standing population by the number of generations it spanned (around 127,000), which they determined by dividing how long the species survived by its estimated generation time of 19 years. * The researchers noted that their estimated population density for the species would translate to roughly 3,800 T. rex in an area the size of California and just two in an area the size of Washington, D.C. Yes, but: Marshall said the precision of the analysis was "low" and this was primarily due to uncertainty about the accuracy of the relationship between living animals' body mass 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 research didn't reach a definitive conclusion but showed the difficulties of estimating the lives of extinct animals. * "It's an exercise in what you can and can't tell," Clark said. "It gives you the chance to say, 'Wow, there really were a lot of these things, and we're not getting a lot of them captured in the fossil record.'" Go deeper: How the meteor that killed dinosaurs created modern forests Go deeper Jacob Knutson 2 hours ago - Politics & Policy Chicago releases video of fatal police shooting of 13-year-old boy A small memorial is seen on April 15 in Chicago where 13-year-old Adam Toledo was shot and killed by a police officer in March. Photo: Kamil Krzaczynski/Getty Images Chicago's independent police review board on Thursday released the body camera footage of an officer's fatal shooting of 13-year-old Adam Toledo on March 29. The big picture: Tension continues to rise nationwide in response to police misconduct and racism. Thursday's footage release comes days after officer Kim Potter fatally shot Daunte Wright in a traffic stop near Minneapolis, where the trial of Derek Chauvin, a former police officer accused of murdering George Floyd, is ongoing. Go deeper (2 min. read) Axios 3 hours ago - Podcasts State AG candidate Jen Jordan talks Georgia's time under the microscope Georgia has become the center of American politics, in an era wherein state issues and officials have taken on elevated national prominence. Axios Re:Cap speaks with Georgia state Sen. Jen Jorden, a Democrat running for attorney general, about her state's time in the national spotlight, if she'd defend the voting law as AG and if Will Smith should have pulled his movie production from her state. Marina E. Franco (Noticias Telemundo) 4 hours ago - Politics & Policy Migrants cite Mexican law as incentive for heading north Monitored by a caretaker, young unaccompanied immigrants, ages 3-9, in a playpen at a Homeland Security holding facility in Donna, Texas, last month. Photo: Dario Lopez-Mills - Pool/Getty Images A Mexican law against the detention of minors who are headed to the U.S. border may unintentionally be encouraging more attempts by children to cross over. The state of play: Teenagers from Honduras told Reuters they decided to cross to the U.S. through Mexico because of the law, which gives them temporary protection from deportation, as they felt safer making the attempt. Go deeper (1 min. read) Axios gets you smarter, faster with news & information that matters. Copyright Axios Media, 2021 About About Axios Advertise with us Careers Events Axios on HBO Axios HQ Privacy and terms Online tracking choices Contact us Subscribe Axios newsletters Axios app Axios podcasts Courses