How many _Tyrannosaurus rex_ walked the Earth?


The Conversation US 16 April, 2021 - 03:16pm 20 views

How many T rexes were there?

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. NBC News2.5 billion T. rex roamed Earth, but not all at once, study finds

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.

Read full article at The Conversation US

2.5 billion T. rex roamed Earth, study finds

Yahoo! Voices 16 April, 2021 - 07:16pm

That's how many scientists think roamed the earth

Researchers factored in size, life expectancy, and geographic range

T. rexes inhabited North America for 2.4 million years

Their skulls alone were about 5 feet long

(CHARLES MARSHALL, UNIVERSITY OF CALIFORNIA MUSEUM OF PALEONTOLOGY DIRECTOR): "The key step is using data from living animals, where there's a clear relationship between population density - the number of individuals per unit area and body mass. There are relatively few elephants. There are a lot more zebra. There are bucket loads of of rabbits and mice."

"We computed the generation time for the first time at about 19 years. The geologic longevity is roughly 2.5 million years. That means it lasted for about 125,000 generations. Our species has been around for about a tenth that. And multiplying the number of generations by the standing population size gave us the 2.5 billion."

T. rexes have been extinct for 66 million years

- The key step is using data from living animals where there's a clear relationship between population density the number of individuals per unit area and body mass. There are relatively few elephants, there are a lot more zebra, there are bucket loads of of rabbits and mice.

We computed computer generation time for the first time, at about 19 years, the geologic longevity is roughly 2 and 1/2 billion years. That means it lasted for about 125,000 generations. Our species has been around for about a tenth that. And multiplying the number of generations by the population standing population size gave us the 2.5 billion.

One Tyrannosaurus rex seems scary enough. 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. 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.

If one Tyrannosaurus rex - the school bus-sized meat-eating dinosaur that stalked the Cretaceous Period landscape - seems impressive, how about 2.5 billion of them? Researchers on Thursday unveiled the first calculation of the total T. rex population during the estimated 2.4 million years that this fearsome species inhabited western North America during the twilight of the age of dinosaurs. They considered factors including the size of its geographic range, its body mass, growth pattern, age at sexual maturity, life expectancy, duration of a single generation and the total time that T. rex existed before extinction 66 million years ago.

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