What do scientists and paleontologists call dinosaurs?

Researchers calculate T-Rex number on Earth

Tyrannosaurus rex is probably the most famous dinosaur of the Cretaceous Period. But how many of the giants once lived on earth? Researchers dare to make an estimate.

From its creation to its extinction, up to two and a half billion specimens of Tyrannosaurus rex may have trudged across the North American continent. US researchers calculated this number taking into account the body mass and energy requirements of the animals, among other things. Since many aspects of the life of the prehistoric giants have not been clarified, it could also have been a lot less, the researchers report in the journal "Science".

The starting point for the investigation was a question that the paleontologist and study director Charles Marshall has often asked himself: "When I hold a fossil in my hand, I can only wonder how unlikely it is that this monster was millions of years ago and I now hold part of its skeleton in my hand. And then I asked myself: How unlikely is it exactly? ", said the researcher in a press release from the University of California. In other words: how many animals once lived on earth and could have left bones?

To estimate this, Marshall and his team first determined the body mass of an adult T. rex. In the case of living species, this can be used to estimate the size of the population: the larger the body of the animals, the fewer there are of them. This law is known among experts as Damuth's Law.

The connection is clear, but the respective ecological conditions also play a role, the researchers call an uncertainty in the calculations. Jaguars and hyenas are about the same size, but the density of hyenas in their habitat is about 50 times higher than that of jaguars.

A fully grown T-Rex weighed around 5,200 kilograms

The research team assumes that a T. rex had an energy requirement somewhere between that of a lion and that of a Komodo dragon, the largest lizard living today. The T. rex was one of the largest carnivores that ever existed. For a full-grown T. rex, the scientists assumed an average weight of 5200 kilograms and a lifespan of around twenty years.

Together with other factors, they determined that an average of one T. rex could have lived in a hundred square kilometers. For comparison, the scientists explain that about two T. rex could have lived in an area the size of the city of Washington.

Around 20,000 adult Tyrannosaurus rex may have been living on Earth at the same time. Based on around 127,000 generations until the giants disappeared, it could have been up to 2.5 billion. T. rex lived in the Cretaceous period 68 to 66 million years ago

Only 1 in 80 million dinosaurs have been found to date

The researchers are aware that their calculations are fraught with numerous uncertainties and that the range of fluctuation is considerable. One of the reasons for this is that it is not fully understood how the animals' metabolism worked.

The number of animals living on earth at the same time is accordingly between 1300 and 328,000, the total number of T. rex between 140 million and 42 billion. "In our study, we focused on developing robust constraints on the variables we need for our calculations, rather than making the best estimates of themselves," explains Marshall.

To date, the remains of fewer than a hundred different Tyrannosaurus rex have been found, often just individual bones. 32 skeletons are currently exhibited in museums. Based on this number, the researchers report that around 1 in 80 million animals is found. At the fossil-rich site in the US state of Montana, it could be one of around 16,000 of the specimens that once lived there.

"It's surprising how much we actually know about these dinosaurs and how much more we can calculate from them," says Marshall. "Our knowledge of T. rex has expanded so much in the last few decades thanks to more fossils, more ways to analyze them, and better ways to incorporate the information about the many known fossils."