At least 2.5 billion T. rex would have lived on Earth
Paleontologists have assessed the number of T. rex that once roamed the Earth and found that for two to three million years their population stagnated at around 20,000 or so.
According to the new estimates, the T. rex fossils we have today are in fact extremely rare.
?If you took the urge to travel back in time to visit Montana 67 million years ago, you would enter the realm of a true tyrant: the iconic Tyrannosaurus rex . Before venturing into this lost world, you might want to know how far away is, on average, the closest T. rex
It may seem impossible to determine, but after combing through two decades of data on the apex predator, a new study has managed to estimate the population density of this animal. In all likelihood, the nearest T. rex would be within a 15 mile radius…or possibly much closer.
The new study in question, published in the journal Science , also sets out to translate these population densities into estimates of the total number of T. rex that have lived on Earth. On average, researchers estimate that at any given time there would have been about 20,000 T. rex , and that 127,000 generations of these dinosaurs would have followed one another. These averages imply that a total of 2.5 billion T. rex would have lived across their native North America, from Alaska to Mexico, over a period of about two to three million years.
This is not the first time that scientists have tried to estimate the number of T. rex that have walked on the earth's surface. Moreover, the average population density established in this new article, about one T. rex per 108 km², is not so far from a previous estimate published in 1993 . However, the new study used the latest biological data for T. rex to try to pinpoint the lower and upper limits of the total population.
After running several million computer simulations, each composed of slightly different variables, the study determined that the total number of T. rex must be between 140 million, for the lower limit, and 42 billion, for the upper limit. with an average of around 2.5 billion. At any given time, there would have been between 1,300 and 328,000 living T. rex , with an average of 20,000 specimens.
"It's really fascinating to see someone use everything we know about T. rex to try to assess their population dynamics," said Holly Woodward, a paleontologist at the Oklahoma State University Center for Health Sciences which did not take part in the study. “It's interesting and kind of funny that it hasn't been done on this kind of scale yet. »
CENSUS OF T. REX
Over the past twenty years, researchers have multiplied the discoveries about the T. rex , including their lifespan (about 28 years), the age of their sexual maturity (around 15.5 years), or their weight (7 tons on average). These data made it possible to calculate the approximate generation time of T. rex , plus or minus 19 years, as well as their average body mass over time.
To arrive at the T. rex population estimate , researchers exploited a theory linking body mass and population density in living animals . On average, when body mass increases by a factor of 10, density decreases by more than four-fifths, a trend known as Damuth's Law.
Ecologist at the University of California, Santa Barbara, John Damuth discovered this relationship by gathering thirty years of ecological data on living mammals. That said, Damuth's law is not infallible, as there is a great diversity of habitats and lifestyles among animals. For example, spotted hyenas and jaguars have similar body mass, both are predators, but the population density of hyenas is 50 times that of jaguars.
Applied and adapted to T. rex , which is not a mammal, Damuth's law led to a total of between 140 million and 42 billion representatives.
“In paleontology, estimates are complex. Instead of focusing on the estimate, I preferred to frame it. Is it possible to set strong low and high limits for this value? explains the lead author of the study, Charles Marshall , a paleontologist at the University of California at Berkeley.
FIXED FOREVER
In addition to the better appreciation of the number of these elephantine predators, Marshall and his team were able to extract from this data an estimate of the frequency of formation of the fossils. The question was whether the chances of fossilization of a T. rex could be quantified in the same way, for example, as the risk of being struck by lightning.
To date, there are about 100 known specimens of T. rex , but 40% of them are privately or commercially owned and cannot be reliably studied. That's why Marshall's team only counted 32 post-juvenile T. rex fossils for this study, those held by public institutions.
If all 2.5 billion T. rex produced only these 32 fossils, then the fossilization would concern only 1 out of 80 million T. rex . Even admitting that this percentage is higher and that we have not yet found all the fossils, such a low probability shows how rare it is for a carcass to find itself buried quickly enough and in the right chemical conditions to mineralize and produce a fossil. “If the T. rex were a thousand times less abundant, 2.5 million instead of 2.5 billion, we might never have found their trace,” Marshall illustrates.
The method developed by Marshall and his team of researchers could be applied to other extinct creatures. Among the dinosaurs, the researchers mention in particular a herbivore from the Cretaceous, Maiasaura , known from the hundreds of specimens discovered, ranging from newborns to adults.
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