Billions of fearsome T-Rex dinosaurs had once roamed North America
UC Berkeley estimate is first attempted headcount of world's most famous dinosaur
It is the most famous dinosaur of all time, as long as school bus, weighing more than 5 tons, with a mouth full of razor sharp teeth. Scientists know a lot about the Tyrannosaurus rex — the star of films from Jurassic Park to King Kong — from fossils.
But until now, researchers haven’t known how many of the most fearsome terrestrial carnivores were alive during during their heyday. A new study out Thursday from paleontologists at the University of California, Berkeley estimates that there were about 20,000 T.rexes alive at one time, roaming a range that is now the West Coast of North America, from Southern Canada through the Rocky Mountains and California to New Mexico.
The long-extinct meateater was around for a long time, living 68 million to 66 million years ago. The scientists estimated they spanned 127,000 generations as the world’s apex predator. The study’s mindboggling conclusion: Over their entire reign, roughly 2.5 billion individual T.rexes lived on Earth.
So far over the past century, scientists have found about 100 fossils, mostly in the Dakotas, Montana and Colorado. There are only 32 largely complete T.rex skeletons in museums around the world.
“Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them,” said Charles Marshall, director of the University of California Museum of Paleontology, and the lead author on the study published Thursday in the journal Science.
The largest, most complete T.rex skeleton ever found was discovered in South Dakota in 1990 by Sue Hendrickson, an amateur paleontologist. The dinosaur, nicknamed “Sue,” sits in the Field Museum in Chicago, which paid the landowner $7.6 million for it.
Marshall and his colleagues analyzed the relationship between body mass, reproductive maturity and population density for living animals, and compared it to what is known about T.rexes.
The dinosaur’s name means “tyrant lizard king.” The species was named in 1905 by Henry Fairfield Osborne, president of the American Museum of Natural History. He took the name from the Greek word tyrannos, meaning “tyrant” and sauros, meaning “lizard,” then for flair, added the Latin word “Rex,” which means “king.”
In the most recent study, the UC scientists calculated that each generation lasted about 19 years, and that the average population density was about 1 for every 100 square kilometers. Put another way, that’s about one T.rex for every 25,000 acres. Looked at through a modern view, that means that at any time during the Upper Cretaceous period, when they lived, an area the size of San Francisco would have had one T.rex gobbling up the local plant-eating dinosaurs.
An area the size of Oakland would have had two. San Jose would have had four, and Los Angeles 12. An area the size of Yosemite National Park would have had 30. And California would have had about 4,000.
Back then, before a massive asteroid hit the Earth near present-day Mexico 66 million years ago and wiped out the dinosaurs, T.rexes were found in an area that includes much of the American West. But the landscape then wasn’t anywhere near the same shape as North America now. It was an island continent known as Laramidia, separated by an ocean from what is the East Coast of the United States today.
Marshall notes that there is wide variability in his estimates, which were based on comparisons to Komodo dragons and lions.
He said he expects other researchers to debate the numbers, which are based on calculations and computer code that could help scientists estimate populations of other fossilized creatures, and gain a better understanding of how many of each type may yet to be discovered.
“In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it,” he said. “It’s surprising how much we actually know about these dinosaurs and, from that, how much more we can compute. Our knowledge of T.rex has expanded so greatly in the past few decades thanks to more fossils, more ways of analyzing them and better ways of integrating information over the multiple fossils known.”