Billions of T. rexes roamed Earth over their lifetime, study says

Science

CNET 18 April, 2021 - 05:15pm 31 views

How many T rexes were there?

He added: “In spite of the uncertainties associated with most of the model parameters the paper comes up with a solid qualitative result.” If the 20,000 number is correct, over the 2.4 million years that T. rex walked the Earth, there would have been a total of some 2.5 billion adults that ever lived. The New York TimesHow Many Tyrannosaurus Rexes Ever Lived on Earth? Here’s a New Clue.

Gizmodo reported on the new study, which UC Berkeley paleontologist, Charles Marshall, executed on a whim. Marshall, who teamed up with some of his students for the study published in the journal Science, said in a UC Berkeley press release that he originally wanted to know how likely it is to find dinosaur fossils. (For no particular reason.)

“The project just started off as a lark, in a way,” Marshall said in the press release. “When I hold a fossil in my hand, I can’t help [wonder] at the improbability that this very beast was alive millions of years ago, and here I am holding part of its skeleton…[and the] question just kept popping into my head, ‘Just how improbable is it?”

To find out that probability, Marshall and his student team focused in on T. rex, seeking a figure for its population size during any given year of its existence. As well as a model for the total number of T. rex that roamed Earth during the Cretaceous Period; the epoch lasting from from 145 to 66 million years ago.

According to Marshall and his team’s models, 20,000 adult T. rex likely roamed together at any one time in their history. The researchers estimate each one of the 40-foot-long, 14,000-pound reptiles would’ve each needed about 40 square miles of land. And that they would’ve had a total of 900,000 square miles of North American continent across which to roam.

Assuming a generational length of 19 years, and a species lifespan of 2.5 million years, that would mean 2.5 billion T. rex in total roamed Earth. And that’s not even counting the juveniles.

Unfortunately, Marshall and his team acknowledge that there’s a wide margin of error for their estimate. The researchers say they could be overestimating the number by a factor of up to 100; the estimation’s accuracy depends on T. rex‘s true average mass and population density. If the number is correct, however, for every one T. rex fossil we’ve found so far, there should be 80 million more. Although we’re sure the dino-killing asteroid wiped out a lot of those bones.

v2.08 – © Nerdist All Rights Reserved

Read full article at CNET

Palaeontology: More than 2.5 BILLION T. Rexes roamed the Earth over their 2.5 million years

Daily Mail 17 April, 2021 - 07:11pm

By Ian Randall For Mailonline

Tyrannosaurus rex. Their name means 'tyrant lizard king' — and as far as popular culture goes, they certainly ruled the dinosaurs. But just how many were there?

According to experts from California, the answer is a whopping 2.5 billion of the beasts over the 2.5 million years they roamed North America in the Late Cretaceous.

Around 20,000 adult T. rexes were probably alive at any given point during the species' existence — give or take a factor of ten, the researchers have estimated.

T. rex — along with the rest of the dinosaurs — went extinct in the wake of a devastating asteroid strike on the Earth some 66 million years ago.

Tyrannosaurus rex. Their name means 'tyrant lizard king' — and as far as popular culture goes, they certainly ruled the dinosaurs. But just how many were there? According to experts from California, the answer is a whopping 2.5 billion of the beasts over the 2.5 million years they roamed North America in the Late Cretaceous. Pictured: an artist's impression of T. rexes

Tyrannosaurs rex was a species of bird-like, meat-eating dinosaur.

It lived between 68–66 million years ago in what is now the western side of North America.

They could reach up to 40 feet (12 metres) long and 12 feet (4 metres) tall.

More than 50 fossilised specimens of T. rex have been collected to date.

The monstrous animal had one of the strongest bites in the animal kingdom.

An artist's impression of T. rex

'The project just started off as a lark, in a way,' paper author and palaeontologist Charles Marshall of the University of California, Berkeley explained.

'When I hold a fossil in my hand, I can't help wondering at the improbability that this very beast was alive millions of years ago, and here I am holding part of its skeleton.'

'The question just kept popping into my head, "Just how improbable is it? Is it one in a thousand, one in a million, one in a billion?" '

'And then I began to realize that maybe we can actually estimate how many were alive, and thus, that I could answer that question.'

Given the incomplete nature of the fossil record, the notion of being able to reliably estimate the population numbers of long-extinct species has long been dismissed as an impossibility — most notably by the US palaeontologist George Gaylord Simpson.

'As Simpson observed, it is very hard to make quantitative estimates with the fossil record,' Professor Marshall conceded. 

'We focused in developing robust constraints on the variables we needed to make our calculations, rather than on focusing on making best estimates.'

The team's calculation raises questions — such as why, if the species was so numerous, fewer than 100 individual T. rex have been found, many of which are known from single bones only.

'There are about 32 relatively well-preserved, post-juvenile T. rexes in public museums today,' Professor Marshall explained.

'Of all the post-juvenile adults that ever lived, this means we have about one in 80 million of them.'

'If we restrict our analysis of the fossil recovery rate to where T. rex fossils are most common, a portion of the famous Hell Creek Formation in Montana,' he continued. 

'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.'

'We were surprised by this number — this fossil record has a much higher representation of the living than I first guessed.' 

'It could be as good as one in a 1,000, if hardly any lived there, or it could be as low as one in a quarter million, given the uncertainties in the estimated population densities of the beast.'

In their study, Professor Marshall and colleagues consulted both the existing scientific literature and the expertise of peers.

They calculated that T. rex likely reached sexual maturity at 15.5 years and it probably lived into its late 20s.

The average body mass of adults of the species was likely 819 stone (5,200 kilograms) — but they could grow to as heavy as 1102 stone (7,000 kilograms). 

These estimates (combined with Damuth's Law, discussed further below, which links body mass to population density) allowed them to calculated that each generation lasted for around 19 years and that the average population density was about one dinosaur for every 39 square miles (100 sq. km).

After estimating that the geographic range of T. rex was about 0.9 million square miles (2.3 million sq. km) and factoring in their temporal range of around 2.5 million years, the team arrived at a standing population size of 20,000 individual dinosaurs.

Over the total of some 127,000 generations the species would have lived, that equates to some 2.5 billion individuals overall, the researchers concluded.

'It's surprising how much we actually know about these dinosaurs and, from that, how much more we can compute,' said Professor Marshall. 'Our knowledge of T. rex has expanded so greatly in the past few decades thanks to more fossils, more ways of analysing them and better ways of integrating information over the multiple fossils known.' Pictured: a mounted cast of T. rex skeleton on display outside the University of California Museum of Paleontology

The team's estimate certainty come with large uncertainties. 

For example, while there was most likely around 20,000 adult T. rexes at any given time, the so-called '95 per cent confidence interval' — in which there is a 95 per cent chance of finding the real number — ranges from 1,300 to 328,000 individuals.

Given this, the total number of T. rexes across time could have been anywhere from 140 million to 42 billion, the researchers explained.

The team used so-called 'Monte Carlo' computer simulations to determine how the uncertainties in their data led to uncertainties in their final result.

According to Professor Marshall, the greatest uncertainty stemmed from outstanding questions about the exact nature of T. rex's ecology — including how warm-blooded the creature was.

The calculations relied on data published by ecologist John Damuth of the University of California Santa Barbara which associates body mass to population density in living animals — a relationship dubbed 'Damuth's Law'.

While the relationship is strong, Professor Marshall explained, ecological difference can result in large variations in population densities for animals that otherwise have similar physiologies.

For example, hyenas and jaguars are around the same size — but the latter can be found with populations densities  some 50 times greater than the big cats.

'Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship spans about two orders of magnitude,' Professor Marshall said. 

'Surprisingly, then, the uncertainty in our estimates is dominated by this ecological variability and not from the uncertainty in the palaeontological data we used.' 

For their calculations, the team elected to regard T. rex as a predator whose energy requirements lay halfway between those of a lion and a Komodo dragon — which is the largest lizard alive on the Earth.

The team also chose to ignore juvenile T. rexes, which are both underrepresented in the fossil record and — recent research has suggested — may have lived apart from adults, pursued different prey and behaved almost like a different predator species.

The team chose to ignore juvenile T. rexes (one of which is depicted above), which are both underrepresented in the fossil record and — recent research has suggested — may have lived apart from adults, pursued different prey and behaved almost like a different predator species

'In some ways, this has been a paleontological exercise in how much we can know, and how we go about knowing it,' said Professor Marshall.

'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 analysing them and better ways of integrating information over the multiple fossils known.'

Professor Marshall said that he expects his peers to quibble with many, if not most of the numbers involved in his team's estimate.

The researchers have made the computer code they used to estimate T. rex numbers available to other researchers — saying that it could lay a foundation for estimating how many species might be missing from our understanding.

'With these numbers, we can start to estimate how many short-lived, geographically specialized species we might be missing in the fossil record,' Professor Marshall said.

'This may be a way of beginning to quantify what we don't know.'

The full findings of the study were published in the journal Science.

Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world's species were obliterated.

This mass extinction paved the way for the rise of mammals and the appearance of humans.

The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event.

The asteroid slammed into a shallow sea in what is now the Gulf of Mexico.

The collision released a huge dust and soot cloud that triggered global climate change, wiping out 75 per cent of all animal and plant species.

Researchers claim that the soot necessary for such a global catastrophe could only have come from a direct impact on rocks in shallow water around Mexico, which are especially rich in hydrocarbons.

Within 10 hours of the impact, a massive tsunami waved ripped through the Gulf coast, experts believe.

Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world's species were obliterated. The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event (stock image)

This caused earthquakes and landslides in areas as far as Argentina.

But while the waves and eruptions were  The creatures living at the time were not just suffering from the waves - the heat was much worse.

While investigating the event researchers found small particles of rock and other debris that was shot into the air when the asteroid crashed.

Called spherules, these small particles covered the planet with a thick layer of soot.

Experts explain that losing the light from the sun caused a complete collapse in the aquatic system.

This is because the phytoplankton base of almost all aquatic food chains would have been eliminated.

It's believed that the more than 180 million years of evolution that brought the world to the Cretaceous point was destroyed in less than the lifetime of a Tyrannosaurus rex, which is about 20 to 30 years.

The comments below have not been moderated.

The views expressed in the contents above are those of our users and do not necessarily reflect the views of MailOnline.

By posting your comment you agree to our house rules.

Do you want to automatically post your MailOnline comments to your Facebook Timeline?

Your comment will be posted to MailOnline as usual.

Do you want to automatically post your MailOnline comments to your Facebook Timeline?

Your comment will be posted to MailOnline as usual

We will automatically post your comment and a link to the news story to your Facebook timeline at the same time it is posted on MailOnline. To do this we will link your MailOnline account with your Facebook account. We’ll ask you to confirm this for your first post to Facebook.

You can choose on each post whether you would like it to be posted to Facebook. Your details from Facebook will be used to provide you with tailored content, marketing and ads in line with our Privacy Policy.

Part of the Daily Mail, The Mail on Sunday & Metro Media Group

Billions of fearsome T.rex dinosaurs once roamed North America, new study shows, maybe in your backyard

The Mercury News 17 April, 2021 - 07:11pm

It is the most famous dinosaur of all time, as long as a 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 about 20,000 T.rexes were 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 meat-eater 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 mind-boggling 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.”

Get Morning Report and other email newsletters

How many T. rexes were there? Billions.

UC Berkeley 17 April, 2021 - 07:11pm

Over approximately 2.5 million years, North America likely hosted 2.5 billion Tyrannosaurus rexes, a minuscule proportion of which have been dug up and studied by paleontologists, according to a UC Berkeley study. (Image by Julius Csotonyi, courtesy of Science magazine)

How many Tyrannosaurus rexes roamed North America during the Cretaceous period?

That’s a question Charles Marshall pestered his paleontologist colleagues with for years until he finally teamed up with his students to find an answer.

What the team found, to be published this week in the journal Science, is that about 20,000 adult T. rexes probably lived at any one time, give or take a factor of 10, which is in the ballpark of what most of his colleagues guessed.

What few paleontologists had fully grasped, he said, including himself, is that this means that some 2.5 billion lived and died over the approximately 2 1/2 million years the dinosaur walked the earth.

Until now, no one has been able to compute population numbers for long-extinct animals, and George Gaylord Simpson, one of the most influential paleontologists of the last century, felt that it couldn’t be done.

Marshall, director of the University of California Museum of Paleontology, the Philip Sandford Boone Chair in Paleontology and a UC Berkeley professor of integrative biology and of earth and planetary science, was also surprised that such a calculation was possible.

“The project just started off as a lark, in a way,” he said. “When I hold a fossil in my hand, I can’t help wondering at the improbability that this very beast was alive millions of years ago, and here I am holding part of its skeleton — it seems so improbable. The question just kept popping into my head, ‘Just how improbable is it? Is it one in a thousand, one in a million, one in a billion?’ And then I began to realize that maybe we can actually estimate how many were alive, and thus, that I could answer that question.”

A cast of a T. rex skeleton on display outside the UC Museum of Paleontology in the Valley Life Sciences Building. The original, a nearly complete skeleton excavated in 1990 from the badlands of eastern Montana, is on display at the Smithsonian Institution in Washington, DC. (UC Berkeley photo by Keegan Houser)

Marshall is quick to point out that the uncertainties in the estimates are large. While the population of T. rexes was most likely 20,000 adults at any give time, the 95% confidence range — the population range within which there’s a 95% chance that the real number lies — is from 1,300 to 328,000 individuals. Thus, the total number of individuals that existed over the lifetime of the species could have been anywhere from 140 million to 42 billion.

“As Simpson observed, it is very hard to make quantitative estimates with the fossil record,” he said. “In our study, we focused in developing robust constraints on the variables we needed to make our calculations, rather than on focusing on making best estimates, per se.”

He and his team then used Monte Carlo computer simulation to determine how the uncertainties in the data translated into uncertainties in the results.

The greatest uncertainty in these numbers, Marshall said, centers around questions about the exact nature of the dinosaur’s ecology, including how warm-blooded T. rex was. The study relies on data published by John Damuth of UC Santa Barbara that relates body mass to population density for living animals, a relationship known as Damuth’s Law. While the relationship is strong, he said, ecological differences result in large variations in population densities for animals with the same physiology and ecological niche. For example, jaguars and hyenas are about the same size, but hyenas are found in their habitat at a density 50 times greater than the density of jaguars in their habitat.

A critical part of the analysis was estimating T. rex’s ecological niche using a plot, called Damuth’s Law, of body mass versus population density for living mammals. (Chart courtesy of John Damuth, UC Santa Barbara)

“Our calculations depend on this relationship for living animals between their body mass and their population density, but the uncertainty in the relationship 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.”

As part of the calculations, Marshall chose to treat T. rex as a predator with energy requirements halfway between those of a lion and a Komodo dragon, the largest lizard on Earth.

The issue of T. rex‘s place in the ecosystem led Marshall and his team to ignore juvenile T. rexes, which are underrepresented in the fossil record and may, in fact, have lived apart from adults and pursued different prey. As T. rex crossed into maturity, its jaws became stronger by an order of magnitude, enabling it to crush bone. This suggests that juveniles and adults ate different prey and were almost like different predator species.

This possibility is supported by a recent study, led by evolutionary biologist Felicia Smith of the University of New Mexico, which hypothesized that the absence of medium-size predators alongside the massive predatory T. rex during the late Cretaceous was because juvenile T. rex filled that ecological niche.

The UC Berkeley scientists mined the scientific literature and the expertise of colleagues for data they used to estimate that the likely age at sexual maturity of a T. rex was 15.5 years; its maximum lifespan was probably into its late 20s; and its average body mass as an adult — its so-called ecological body mass, — was about 5,200 kilograms, or 5.2 tons. They also used data on how quickly T. rexes grew over their life span: They had a growth spurt around sexual maturity and could grow to weigh about 7,000 kilograms, or 7 tons.

A T. rex jaw collected in 1977 in Montana from the Hell Creek Formation by the late UCMP paleontologist Harley Garbani. (©2011 University of California Museum of Paleontology)

From these estimates, they also calculated that each generation lasted about 19 years, and that the average population density was about one dinosaur for every 100 square kilometers.

Then, estimating that the total geographic range of T. rex was about 2.3 million square kilometers, and that the species survived for roughly 2 1/2 million years, they calculated a standing population size of 20,000. Over a total of about 127,000 generations that the species lived, that translates to about 2.5 billion individuals overall.

With such a large number of post-juvenile dinosaurs over the history of the species, not to mention the juveniles that were presumably more numerous, where did all those bones go? What proportion of these individuals have been discovered by paleontologists? 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.”

“If we restrict our analysis of the fossil recovery rate to where T. rex fossils are most common, a portion of the famous Hell Creek Formation in Montana, 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,” he added. “We were surprised by this number; this fossil record has a much higher representation of the living than I first guessed. It could be as good as one in a 1,000, if hardly any lived there, or it could be as low as one in a quarter million, given the uncertainties in the estimated population densities of the beast.”

Marshall expects his colleagues will quibble with many, if not most, of the numbers, but he believes that his calculational framework for estimating extinct populations will stand and be useful for estimating populations of other fossilized creatures.

The tooth of a tyrannosaur – not a T. rex – where Charles Marshall found it in Montana in 2019. While T. rex is an exclusively North American dinosaur, several other tyrannosaur species have been discovered in North America and Asia as well. (UC Berkeley photo by Charles Marshall)

“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.”

The framework, which the researchers have made available as computer code, also lays the foundation for estimating how many species paleontologists might have missed when excavating for fossils, he said.

“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.”

Marshall’s co-authors are UC Berkeley undergraduate Connor Wilson and graduate students Daniel Latorre, Tanner Frank, Katherine Magoulick, Joshua Zimmt and Ashley Poust, who is now a postdoctoral fellow at the San Diego Natural History Museum.

View all articles by Robert Sanders

When desalinating seawater or waste water, removing salt isn't always enough. A new polymer membrane strips out tox… https://t.co/NYeGoQ15L5

Billions of fearsome T.rex dinosaurs once roamed North America, new study shows, maybe in your backyard

The Mercury News 15 April, 2021 - 01:00pm

It is the most famous dinosaur of all time, as long as a 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 about 20,000 T.rexes were 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 meat-eater 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 mind-boggling 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.”

Get Morning Report and other email newsletters

Earth

Science Stories