How many T rexes were there?
To date, fewer than 100 T. rex individuals have been found, many represented by a single fossilized bone. "There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today," he said. "Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them." Patch.comUC Berkeley: How Many T. Rexes Were There? Billions.
This is the first attempt to calculate total T. rex numbers.
Of note, the finding includes only post-juvenile T. rex individuals. That's because younger T. rex likely lived in different niches and ate different foods than older individuals did; moreover, they didn't always survive to maturity, and so weren't included in the final tally, the researchers said.
The finding, once thought impossible, is the first calculation for the population of any extinct beast that lived long ago and may open the door to similar calculations for other extinct creatures, the researchers said.
That said, the study's researchers are transparent about the new research making a few assumptions. For instance, the T. rex population was likely about 20,000 at any one time, but the 95% confidence range — the range of numbers in which there's a 95% chance the true number falls — is 1,300 to 328,000. In other words, when the T. rex total is calculated (which includes population density, population size at any one time, generation time and total number of generations), the number of T. rex individuals that ever lived could be anywhere from 140 million to 42 billion, the researchers said.
"As Simpson observed, it is very hard to make quantitative estimates with the fossil record," study lead researcher Charles Marshall, director of the University of California Museum of Paleontology, the Philip Sandford Boone chair in paleontology, said in a statement. "In our study, we focused [on] developing robust constraints on the variables we needed to make our calculations, rather than on focusing on making best estimates, per se," added Marshall, who is also a professor of integrative biology and of Earth and planetary science at the University of California, Berkeley.
"Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship [for T. rex] spans about two orders of magnitude," Marshall said. "Surprisingly, then, the uncertainty in our estimates is dominated by this ecological variability and not from the uncertainty in the paleontological data we used."
These estimates allowed them to calculate that each T. rex generation lasted about 19 years and that these dinosaurs had an average population density of about 1 T. rex per 38 square miles (100 square km).
According to these calculations, billions of T. rexes existed, but relatively few T. rex fossils have been recovered. Current records show that fewer than 100 T. rex individuals have been unearthed, and many of those are each known from just one fossilized bone.
"There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today," Marshall said. "Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them."
However, this number is higher in T. rex hotspots, including at the famous Hell Creek Formation in Montana, where T. rex fossils are more likely to be found. In these hotspots, "we estimate we have recovered about one in 16,000 of the T. rexes that lived in that region over that time interval that the rocks were deposited," Marshall said.
He acknowledged that other researchers may debate some of the assumptions his team made but that overall, the methods he used can provide a useful method for estimating extinct populations.
"I think it was thought-provoking," Erickson told Live Science. Despite the number of assumptions the researchers made, "I think they got it as close as you can. …They really had to bridge so many different fields to put this together, and I think they should be commended for that."
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17 April, 2021 - 10:24am
FILE – In this Tuesday, March 7, 2006 file photo, life-sized Tyrannosaurus rex models are unloaded for a dinosaur exhibition in Potsdam, Germany. A study released on Thursday, April 15, 2021 calculates that 2.5 billion Tyrannosaurus rex prowled North America over a couple million years or so, with maybe 20,000 at any given time. (AP Photo/Sven Kaestner)
One Tyrannosaurus rex seems scary enough. Now picture 2.5 billion of them. That’s how many of the fierce dinosaur king probably roamed Earth over the course of a couple million years, a new study finds.
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 Thursday’s journal Science. 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.
“That’s a lot of jaws,” said study 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 1.2 million to 3.6 million 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, D.C., or 3,800 in California, the study said.
“Probably like a lot of people, I literally did a double-take to make sure that my eyes hadn’t deceived me when I first read that 2.5 billion T. rexes have ever lived,” said Macalester College paleobiologist Kristi Curry Rogers, who wasn’t part of the study.
Marshall said the estimate helps scientists figure the preservation rate of T. rex fossils and underscores how lucky the world is 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.
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.
The science about the biggest land-living carnivores of all time is important, “but the truth, as I see it, is that this kind of thing is just very cool,” said Purdue University geology professor James Farlow.
Follow Seth Borenstein on Twitter at @borenbears.
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After a slow start, China is now giving millions of shots a day. On March 26 alone, it administered 6.1 million shots. A top government doctor, Zhong Nanshan, has announced a June goal of vaccinating 560 million of the country’s 1.4 billion people.
17 April, 2021 - 10:24am
The team’s calculation employed a scientific rule that says the larger an animal the less dense its population will be in a specific area. After that, energy needs were calculated, with estimates ranging between the needs of a Komodo dragon and a larger “flesh eating mammal.”
“Although much can be deduced from fossils alone, estimating abundance and preservation rates of extinct species requires data from living species,” the researchers wrote.
“Here, we use the relationship between population density and body mass among living species combined with our substantial knowledge of Tyrannosaurus rex to calculate population variables and preservation rates for postjuvenile T. rex,” researchers said.
Yet the T. rex population was not all confined to the same place, the research shows. Researchers estimated that at any given time, around 3,000 T. rex would occupy an area the size of California. By contrast, only two would simultaneously inhabit a geographic space the size of Washington, D.C.
Kristi Curry Rogers, a paleobiologist at Macalester College who was not involved in the study, described to the AP her reaction to the sheer size of the estimated T. rex population, saying she was likely as shocked as the next person.
“Probably like a lot of people, I literally did a double-take to make sure that my eyes hadn’t deceived me when I first read that 2.5 billion T. rexes have ever lived,” Rogers said.
17 April, 2021 - 10:24am
As reported by Associated Press, a study conducted by a team at the University of California, Berkeley, made calculations based on body size, sexual maturity and the creatures' energy needs. They were able to calculate the population with the help of a general biology rule of thumb - the bigger the animal, the less dense its population. They measured the amount of energy T-Rex needed to stay alive and added their estimates. If the T-Rex needed more energy then that means the population was less dense.
“We estimate that its abundance at any one time was ~20,000 individuals, that it persisted for ~127,000 generations, and that the total number of T. rex that ever lived was ~2.5 billion individuals, with a fossil recovery rate of 1 per ~80 million individuals or 1 per 16,000 individuals where its fossils are most abundant,” states the study.
Talking about other factors such as sexual maturity, the team factored in that T-Rex reached sexual maturity somewhere around 14 to 17 years old and it lived at most 28 years. The study has been published in the journal Science.
According to Charles Marshall, lead author and director of the University of California Museum of Paleontology, the estimates will help scientists figure out the preservation rate of T-Rex fossils and highlight how lucky it is that the world knows about them.
The report states that about 100 T-Rex fossils have been discovered where 32 of them have enough material to help determine they are adults. Marshall further added that if there had been 2.5 million T-Rex roaming around the Earth and not the whopping 2.5 billion, as calculated by the researchers, the world wouldn’t have ever known of their existence.
16 April, 2021 - 07:11am
Around 2.5 billion Tyrannosaurus rex roamed Earth over millions of years, according to estimates from a study published Thursday.
At any one time, around 20,000 T. rex struck fear into their Cretaceous Period contemporaries, the study in the journal Science estimated.
“That’s a lot of jaws,” study lead author Charles Marshall, director of the University of California Museum of Paleontology, told the Associated Press. “That’s a lot of teeth. That’s a lot of claws.”
The species lasted for approximately 2.4 million years, between 68 million and 66 million years ago, before an asteroid wiped out the entire population. Despite the animal’s status atop the food chain, scientists believe an individual T. rex would’ve been lucky to reach age 30.
The Science study was based on T. rex’s body size, sexual maturity and energy needs. The study’s margin of error suggested the true number of dominant dinos could’ve been between 140 million and 42 billion. No one had previously attempted to determine the all-time T. rex population.
Only 30-40 T. rex fossils have been discovered, complicating the estimate.
Life finds a way — except when an asteroid hits.