If you traveled back to ancient Montana 67 million years ago, you would enter the realm of a tyrant: the iconic predator Tyrannosaurus rex. However, before you venture into the lost world, you may want to know: how close is the average T. rex to you?
It may sound like an impossible thing to know – but after we’ve been crossing for two decades T. rex research, a new study provides estimates of the population density of the animal. In all probability, a T. rex would be within 15 miles of you, if not much closer.
The new study, released last Thursday in Science, also translates these population densities into estimates for how many T. rex ever lived. On average, researchers estimate that about 20,000 T. rex lived at any one time and that about 127,000 generations of the dinosaurs lived and died. These averages imply that a total of 2.5 billion T. rex lived in the species’ native North America, possibly as far north as Alaska and as far south as Mexico, for a period of two to three million years.
This research is not the first time scientists have tried to estimate T. rex numbers. In fact, the average population density in the new article – about one T. rex every 42 square kilometers – looks a lot like a previous estimate published in 1993. But the new study uses the latest T. rex biology research to set highly accurate upper and lower limits for the total population.
After performing millions of computer simulations, each with a slightly different mixture of possible values, the study found that the total T. rex the score can be as low as 140 million and as high as 42 billion, with an average of about 2.5 billion. Similarly, from 1,300 to 328,000 T. rex could have lived at any one time, with 20,000 on average.
‘It’s really exciting that someone is trying to … use everything we know T. rex to try to figure out the population dynamics, ”says Holly Woodward, a paleontologist at the Oklahoma State University Center for Health Sciences who was not involved in the new study. “It’s interesting and nice that it’s not done on this kind of scale.” (Read more about Woodward’s research on how T. rex spent his teens.)
T. rex Accounting
In the last 20 years, researchers have discovered extraordinary amounts T. rex, including how long it lived (about 28 years), when it reached sexual maturity (about 15.5 years old), and how much it weighed when it was an adult (on average about 15,000 pounds). With this data, scientists can calculate T. rexestimated generation time – 19 years, give or take – and the average body mass of T. rex at any given time.
To catch up T. rexpopulation numbers, researchers used a link between body mass and population density among live animals. As body mass increases by an average of 10, population density decreases on average by more than four-fifths – a pattern known as Damuth’s law.
Damuth, an ecologist at the University of California, Santa Barbara, first discovered this pattern by compiling 30 years of ecological data on live mammals. However, Damuth’s law is not iron cloth, as animals differ greatly in their lifestyle and habitat. Spotted hyenas and jaguars, for example, have a similar body mass, and both are predators, but the population density of the hyenas is about 50 times higher.
When applied to T. rex (after correction for the fact that T. rex is not mammal), Damuth’s law implied that the actual total of the dinosaur probably fell within 140 million and 42 billion individual dinosaurs.
‘In paleontology, it’s very difficult to estimate things … so what I started doing was thinking less about estimating something and chopping more at it. Can I put a strong top and bottom edge on it? says lead author Charles Marshall, a paleontologist at the University of California, Berkeley.
From life to the rock
Aside from a better understanding of how many of these elephant-sized predators roamed around, Marshall and his team were able to crunch the numbers to better estimate how often fossils form. Can the chance of a T. rex fossilization is quantified, in the same way that we can calculate the chance of being struck by lightning?
There are a hundred or so known specimens of T. rex, but about two-fifths of it is in private or commercial hands and cannot be studied reliably. To compile a minimum fossil total for the purposes of the study, Marshall’s team limited its score to 32 fossil juveniles. T. rex held in public institutions.
If all the T. rex who ever lived – the estimated 2.5 billion – produced only those 32 fossils, and then only one of the 80 million T. rex after they died, disturbed. Although a higher percentage of the animals have been fossilized and we have yet to find the remains, the mere chance of this chance highlights how rare it is that a carcass is buried fast enough and mineralized in the right chemical conditions to form a fossil. . ‘As T. rex was a thousand times less abundant – if the total was not 2.5 billion, but 2.5 million“We might never have found it,” says Marshall.
The method outlined by Marshall’s team can also be used for other extinct creatures. Among dinosaurs, researchers say the Cretaceous herbivore is one of the best candidates Maiasaura, known from hundreds of copies, from newborns to adults.
For Woodward, one of the most exciting implications of the study is how rare dinosaur fossils really are. If these rates apply to species other than T. rex, researchers may even be able to estimate how many dinosaur species simply did not fossilize at all – and are now irrevocably lost. “Finding out how much we are missing can be just as important as knowing how much we have,” she says.