How many T rexes were there?
Using data from the latest fossil analyses, they concluded that some 20,000 adults likely roamed the continent at any one time, from Mexico to Canada. The species survived for perhaps 2.5 million years, which means that about 2.5 billion lived and died overall. Science DailyHow many T. rexes were there? Billions: Analysis of what's known about the dinosaur leads to conclusion there were 2.5 billion over time
Humans in our current form have been around for perhaps a few hundred thousand years, what seems like an inconceivably long run in comparison to the lifespan of a single human. But even more mind-blowing is the fact that long before we emerged, Tyrannosaurus rex had its run of the place for over 10 times as long.
Now a new study attempts to calculate exactly how many of the terrifying, thundering lizards may have stomped and chomped their way across the Earth over a few million years. The result: probably about 2.5 billion altogether, but the number could actually be as high as 42 billion.
That high-end number is probably less than half the total number of humans that have ever lived, but it's still a lot of huge, hungry prehistoric predators, especially when we consider what a relatively rare find T. rex fossils are for paleontologists.
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"There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today," said Charles Marshall, director of the University of California Museum of Paleontology, in a statement. "Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them."
Marshall led the study, published in the latest issue of the journal Science, which fed known data about the extinct beasts into computer simulations to essentially make educated guesses about their total number.
Billions of towering carnivores living over a few million years is still a much lower population density than that of humans today, of course. The study estimates the total population of T. rexes at any given time was probably about 20,000 adults. Clearly nothing compared to the nearly 8 billion human meatbags hanging around today.
But Marshall and his UC Berkeley colleagues estimate a population density of around one dinosaur every 39 square miles (100 square kilometers). That means that, statistically speaking, during the late Cretaceous period you could have expected a T. rex to be within about 7 miles (11.3 kilometers) of your location. Not exactly a safe environment to do much traveling.
However, there are plenty of uncertainties in the estimates that Marshall and his team came up with. While the simulation found 2.5 billion total T. rexes as its best guess, the correct figure could actually be somewhere in a wide range between 140 million to 42 billion.
"In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it," Marshall 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."
The team is also open-sourcing the computer code used in the research, which they hope may allow paleontologists to estimate how many other species might be missed in excavations.
"With these numbers, we can start to estimate how many short-lived, geographically specialized species we might be missing in the fossil record," he said. "This may be a way of beginning to quantify what we don't know."
One thing is certain for at least one person: Putting a quantity to the historical number of T. rexes brings certain nightmares into sharper focus.
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15 April, 2021 - 02:55pm
Using calculations based on body size, sexual maturity and the creatures’ energy needs, a team at the University of California, Berkeley, figured out just how many T rex lived over 127,000 generations, according to a study in the journal Science on Thursday. It’s a first-of-its-kind number, but just an estimate with a margin of error that is the size of a T rex.
Given uncertainties in the creatures’ generation length, range and how long they roamed, the Berkeley team said the total population could be as little as 140 million or as much as 42 billion with 2.4 billion as the middle value.
“That’s a lot of jaws,” said the study’s lead author, Charles Marshall, director of the University of California Museum of Paleontology. “That’s a lot of teeth. That’s a lot of claws.”
The species roamed North America for about 1.2m to 3.6m years, meaning the T rex population density was small at any one moment. There would be about two in a place the size of the Washington DC, or 3,800 in California, the study said.
Marshall said the estimate would help scientists figure the preservation rate of T rex fossils and underscored how lucky the world was to know about them at all. About 100 or so T rex fossils have been found – 32 of them with enough material to figure they are adults. If there were 2.5 million T rex instead of 2.5 billion, we would probably have never known they existed, he said.
Marshall’s team calculated the population by using a general biology rule of thumb that says the bigger the animal, the less dense its population. Then they added estimates of how much energy the carnivorous T rex needed to stay alive – somewhere between a Komodo dragon and a lion. The more energy required, the less dense the population. They also factored in that the T rex reached sexual maturity somewhere around 14 to 17 years old and lived at most 28 years.
The science about the biggest land-living carnivores of all time was important, “but the truth, as I see it, is that this kind of thing is just very cool”, said James Farlow, a geology professor at Purdue University.