If you traveled back in time 67 million years ago to ancient Montana, you would enter the realm of a tyrant: the iconic predator Tyrannosaurus rex. Before you venture into that lost world, however, you may want to know: on average, how close it is. T. rex for you?
It may seem impossible to know – but after two decades of crushing T. rex research, a new study provides estimates of animal population density. In all likelihood, a T. rex it would be less than 15 miles from you, if not even closer.
The new study, published 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 given time and that about 127,000 generations of dinosaurs lived and died. These averages involve a total of 2.5 billion T. rex lived in the species’s native North America, possibly as far north as Alaska and as far south as Mexico, for 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 work – about one T. rex every 42 square miles – very similar to a previous estimate published in 1993. But the new study uses the latest T. rex biological research to try to set extremely precise 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 number could be up to 140 million and 42 billion, with an average of about 2.5 billion. The same, from 1,300 to 328,000 T. rex it could have been alive at some point, with an average of 20,000.
“It’s very interesting that someone is trying to … use everything we know T. rex to try to account for 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 fun that this wasn’t done on this type of scale.” (Learn more about Woodward’s research on how T. rex spent his adolescence.)
T. rex accountancy
In the last 20 years, researchers have discovered an extraordinary amount T. rex, including how long he lived (about 28 years), when he reached sexual maturity (about 15.5 years) and how much he weighed when he was fully grown (about 15,000 pounds, on average). This data allows scientists to calculate T. rexapproximate generation time – 19 years, give or take – and average body mass of T. rex at any given time.
Get to T. rexPopulation numbers, the researchers took advantage of a relationship between body mass and population density among live animals. On average, as body mass increases by a factor of 10, population density is diluted 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 living mammals. However, Damuth’s Law is not iron, because animals vary greatly in their lifestyle and in their specific habitats. For example, spotted hyenas and jaguars have similar body masses and both are predators, but the population density of hyenas is about 50 times higher.
When applied to T. rex (after I corrected that T. rex it is not a mammal), Damuth’s Law suggested that the true total of the dinosaur probably falls into 140 million and 42 billion individual dinosaurs.
“In paleontology, it’s very difficult to estimate things … so what I’ve started to do is think less about estimating something and more about replacing it. Can I put a sturdy top and bottom edge on it? Says lead author Charles Marshall, a paleontologist at the University of California, Berkeley.
From life to rock
In addition to understanding how many of these elephant-sized predators walked around, Marshall and his team were able to gather numbers to estimate how often fossils form. It could be a chance T. rex fossilization to be quantified in the same way we can calculate the chances of being struck by lightning?
There are a hundred known specimens T. rex, but about two-fifths of them are in private or commercial hands and cannot be reliably studied. So, in order to establish a minimum total number of fossils for the purposes of the study, Marshall’s team limited its number to 32 post-juvenile fossils. T. rex which takes place in public institutions.
If all T. rex that ever lived – about 2.5 billion – produced only those 32 fossils, then only one in 80 million T. rex fossilized after they died. Even though a higher percentage of animals have fossilized and we have not yet found the remains, the minuscule of these quotas underscores how rare it is for a carcass to be buried fast enough and in the right chemical conditions to mineralize and form a fossil. “If T. rex they were a thousand times less abundant – if the total was not 2.5 billion, but 2.5 million“I may never have found him,” says Marshall.
The method that the Marshall team pointed out could also be used for other missing creatures. Among the dinosaurs, researchers say that one of the best candidates is the Cretaceous herbivore Maiasaura, which is known from hundreds of specimens, from newborns to adults.
For Woodward, one of the most interesting implications of the study is just how rare dinosaur fossils are. If these rates are valid for species other than T. rex, researchers might even be able to estimate how many species of dinosaurs simply did not fossilize at all – and are now irrevocably lost in time. “Being able to figure out how much we miss can be just as important as knowing how much we have,” she says.