Researchers on Thursday uncovered the first estimate of the total population of T. rex over an estimated 2.4 million years as this terrifying species inhabited western North America during the twilight of the dinosaur era.
They considered factors including its geographic range size, body weight, growth pattern, age at sexual maturity, life expectancy, one generation duration, and the total lifetime of T. rex before extinction 66 million years ago. They also obeyed a doctrine called Damuth’s law that links population to body weight: the larger the animal, the fewer individuals.
Their analysis found that the total number of T. rex individuals that ever existed was about 2.5 billion, including approximately 20,000 adult adults at one time.
Fossils of more than 40 individuals of T. rex have been found since it was first described in 1905, providing a wealth of information about a beast that thrives in popular imagination.
“I think it’s probably a cult dinosaur,” said paleontologist Charles Marshall, who led the study published in the journal Science. “He’s huge. He has a huge head and huge teeth. It’s really scary. I think we like to feel small. And boy, do you feel small when you’re standing under a skeleton.”
He was among the largest carnivorous dinosaurs, possessing a skull about 1.5 meters long, massive and muscular jaws with the power of bites capable of crushing bones, a bite of jagged teeth the size of a banana, a sharp sense of smell, strong legs and small hands with only two fingers.
Perhaps the most famous T. rex specimen is named Sue from the Field Museum in Chicago, measuring 12.3 meters, weighing about 9 tons and living for about 33 years.
The new study put the weight of the average adult T. rex at 5.2 tons, the average lifespan at 28 years, the generation time at 19 years, the total number of generations of the species at about 125,000, and its geographical range at about 890,000 square miles (2 , 3 million square kilometers).
They calculated an average population density of about one T. rex every approximately 40 square miles (100 square kilometers).
Marshall said he suspected there may have been “maybe two in the Washington area, about one, in the Manhattan area, and one in the San Francisco area.” He added, “But I guess they were clumsy. They followed herds of prey. So instead of being like guards, one in every 40 square miles, they probably moved in groups following prey.”
T. rex fossils have been found in the Canadian provinces of Alberta and Saskatchewan and the U.S. states of Montana, Wyoming, South Dakota, North Dakota, Utah, Colorado, New Mexico, and Texas. T. rex apparently encountered a fiery end when the asteroid crashed into Mexico, exterminating three-quarters of the Earth’s species.
Although the uncertainties in the estimates were great and some of the assumptions can be challenged by other paleontologists, the study was a worthwhile effort to expand understanding of this famous dinosaur, said Marshall, director of the University of California Paleontology Museum and the University of California, Berkeley, a professor of integrative biology.
The formula could be applied to other extinct animals, Marshall added.
Paleontologist and co-author of the study Ashley Poust of the Natural History Museum in San Diego said it is 2.5 billion, but represents only a third of the Earth’s current human population – and 20,000 is just a small town.
(Contributed by agencies)