Free Republic
Browse · Search
General/Chat
Topics · Post Article

Skip to comments.

Paleontologists Stunning Conclusion: 2.5 Billion T. Rexes Roamed North America Over the Cretaceous Period
SciTechDaily ^ | 4/15/2021 | UC Berkeley

Posted on 04/16/2021 1:18:06 PM PDT by LibWhacker

Paleontologists Stunning Conclusion: 2.5 Billion T. Rexes Roamed North America Over the Cretaceous Period

TOPICS:

By University of California - Berkeley April 15, 2021

Tyrannosaurus T-Rex Dinosaur

Analysis of what’s known about the dinosaur leads to conclusion there were 2.5 billion over time.

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.

T. rex Cast at UC Berkeley

A cast of a T. rex skeleton on display outside the UC Museum of Paleontology at the University of California, Berkeley. The original, a nearly complete skeleton excavated in 1990 from the badlands of eastern Montana, is at the Museum of the Rockies in Bozeman, Montana. Credit: Keegan Houser, UC Berkeley

“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.”

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.

“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.

What the fossils tell us

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.

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.

“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.



TOPICS: Science
KEYWORDS: america; billions; cretaceous; namerica; rex; rexes; roamed; trex; tyrannosaurus
Navigation: use the links below to view more comments.
first previous 1-2021-4041-6061-69 next last
To: EnderWiggin1970

Chance mutation cannot explain what we see in the evolutionary record. Something is driving it.


21 posted on 04/16/2021 1:46:42 PM PDT by Seruzawa (The political Left is the Garden of Eden of Incompetence - Marx the Smarter (Groucho))
[ Post Reply | Private Reply | To 17 | View Replies]

To: Nateman

Most interesting new discovery in that is they found the tail of another dino with a T-Rex tooth stuck inside it. The wound had healed, so it means the T-Rex tried to chomp on it while it was alive.


22 posted on 04/16/2021 1:47:49 PM PDT by Renfrew
[ Post Reply | Private Reply | To 4 | View Replies]

To: TexasGator

The sea of billions and billions of T Rexes.


23 posted on 04/16/2021 1:48:30 PM PDT by DannyTN
[ Post Reply | Private Reply | To 13 | View Replies]

To: EnderWiggin1970
it’s only about 1/3 the population of humans alive today.

For an animal that was more than 50 times the mass of an average human.

24 posted on 04/16/2021 1:48:59 PM PDT by LibWhacker
[ Post Reply | Private Reply | To 17 | View Replies]

To: TexasGator

It was a joke, sarcasm.


25 posted on 04/16/2021 1:53:11 PM PDT by SkyDancer (To Most People The Sky's The Limit ~ To A Pilot, It is Home)
[ Post Reply | Private Reply | To 19 | View Replies]

To: entropy12

apparently you missed the “over time” qualifier in the article. Only about 20,000 standing population.

Apex predators always have a smaller population than their prey or famine and cannibalism are next.

Humans figured out a better way.


26 posted on 04/16/2021 1:54:41 PM PDT by Valpal1
[ Post Reply | Private Reply | To 11 | View Replies]

To: DannyTN

“The sea of billions and billions of T Rexes.”

You misread the headline ...


27 posted on 04/16/2021 1:55:12 PM PDT by TexasGator (Z1z)
[ Post Reply | Private Reply | To 23 | View Replies]

To: LibWhacker
Wow, think how many things died in the jaws of those monsters.

The horror! The horror!

28 posted on 04/16/2021 1:55:30 PM PDT by x
[ Post Reply | Private Reply | To 1 | View Replies]

To: Valpal1

“Pfft, pikers. There are 7.5 billion humans right now all at once.”

Not in North America. If you believe this Paleo-nonsense you couldn’t have thrown a rock back then without hitting a T-Rex.


29 posted on 04/16/2021 1:57:42 PM PDT by Brooklyn Attitude (I went to bed on November 3rd 2020 and woke up in 1984.)
[ Post Reply | Private Reply | To 6 | View Replies]

To: odawg

Sharks don’t need arms either. They just swim up and take a bite. If T-Rex had any kind of sprinting ability it would have made for an ambush predator against very large herbivores. But as with most meat-eaters they swing between predator and scavenger.


30 posted on 04/16/2021 2:03:06 PM PDT by Tallguy
[ Post Reply | Private Reply | To 18 | View Replies]

To: Tallguy

“If T-Rex had any kind of sprinting ability...”

One scientists I read said he did, wrote that T-Rex was a roadrunner from hell.


31 posted on 04/16/2021 2:05:06 PM PDT by odawg
[ Post Reply | Private Reply | To 30 | View Replies]

To: LibWhacker

Probably most of them are still around voting Democrat.


32 posted on 04/16/2021 2:07:51 PM PDT by Dad was my hero
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

This sounds a bit like Howard Wolowitz’ calculation of how many single women were in LA area bars on any Friday night and his chances of scoring.


33 posted on 04/16/2021 2:09:02 PM PDT by DeFault User
[ Post Reply | Private Reply | To 1 | View Replies]

To: Valpal1

I instinctively knew BEFORE reading the article there is just no practical way Billions of T-Rex’s could inhabiting at the same time in North America. Of course over 2 or 3 million years that is quite possible.

If humans survive 2 million more years, what will be the cumulative population over that time? Could be beyond the scope of a 64 bit based computer in integer form.


34 posted on 04/16/2021 2:09:05 PM PDT by entropy12 (Thanks President Trump for WARP SPEED availability of covid vaccines.)
[ Post Reply | Private Reply | To 26 | View Replies]

To: LibWhacker

A little help here, I seem to have missed the part where the discuss the T Rex life expectancy and population curve data.


35 posted on 04/16/2021 2:17:54 PM PDT by Recompennation
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

So they don’t know the population accurately.

And they don’t know the range accurately.

And they don’t know the duration accurately...

So I would say their accuracy is +/-ten trillion.


36 posted on 04/16/2021 2:36:25 PM PDT by Pikachu_Dad ("the media are selling you a line of soap)
[ Post Reply | Private Reply | To 10 | View Replies]

To: odawg
I remember that. Bakker.

Paleontologist Robert Bakker memorably described T. rex as "the 20,000-pound roadrunner from Hell"

37 posted on 04/16/2021 2:36:38 PM PDT by Daaave ('You Nexus huh? I design your eyes.')
[ Post Reply | Private Reply | To 31 | View Replies]

To: LibWhacker

Where da feathers 🪶 🪶 🪶 ?


38 posted on 04/16/2021 2:36:57 PM PDT by Pikachu_Dad ("the media are selling you a line of soap)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

Where da feathers 🪶 🪶 🪶 ?


39 posted on 04/16/2021 2:37:05 PM PDT by Pikachu_Dad ("the media are selling you a line of soap)
[ Post Reply | Private Reply | To 1 | View Replies]

To: LibWhacker

Where da feathers 🪶 🪶 🪶 ?


40 posted on 04/16/2021 2:37:12 PM PDT by Pikachu_Dad ("the media are selling you a line of soap)
[ Post Reply | Private Reply | To 1 | View Replies]


Navigation: use the links below to view more comments.
first previous 1-2021-4041-6061-69 next last

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.

Free Republic
Browse · Search
General/Chat
Topics · Post Article

FreeRepublic, LLC, PO BOX 9771, FRESNO, CA 93794
FreeRepublic.com is powered by software copyright 2000-2008 John Robinson