Tyrannosaurus rex - known for short as "T-rex" - is one of the giant dinosaurs that roamed the Earth for a period of 2.5 million years during the Cretaceous period.
However, the number of these dinosaurs was a baffling question for scientists.
Recently, a team of paleontologists at the University of California, Berkeley provided an answer to this question based on some calculations they made.
The study was published in the journal Science on April 16.
According to a press release published by the University of Berkeley commenting on the study, the team estimated the number of dinosaurs that could roam the Earth at the same time at 20 thousand dinosaurs.
Consequently, there are approximately 2.5 billion T-Rex that roamed North America - where they were most likely home - during their 2.5 million years.
This is the first time that scientists can estimate the number of dinosaurs based on some calculations.
It was very difficult to derive any quantitative estimates based on the fossil record.
Environmental differences lead to large differences in dinosaur density distribution (Pixabay)
The uncertainty in counting the number of dinosaurs that roamed the Earth together is very large.
"The total number of dinosaurs that roamed the Earth during that period was estimated to be between 140 million and 42 billion dinosaurs," says Charles Marshall, a professor at the University of California at Berkeley and lead author of the study.
This uncertainty is largely due to the different nature of the dinosaur environment.
Therefore, Marshall and his team relied on the use of computer simulations to determine the uncertainty in the results.
The team's numbers were based on the relationship between body mass and population density - known as Damuth's Law - for the species of living animals that now inhabit the Earth.
Although the results of the correlation inferred from "Damuth's Law" were strong for some animals, "environmental differences lead to large differences in the population density distribution of animals that have the same physiology and the same lifestyle," Marshall adds.
For example, American tigers and hyenas are roughly the same size, but hyenas are 50 times more dense than tigers.
The recent study revealed interesting facts and figures (Al-Jazeera)
Therefore, the team incorporated numbers into computer simulations to reduce the huge discrepancy in the results.
They examined previously published results and polled experts for some numbers.
However, these calculations led to other interesting numbers.
Then the team estimated the geographical range in which the T-Rex dinosaurs were found, only to find that it was about 2.3 million square kilometers.
Based on these figures, the number of dinosaurs that existed together at the same time was estimated at 20 thousand dinosaurs.
And because this species has aged for a period of 2.5 million years - a succession of 127 thousand generations - scientists have concluded that the total number of these dinosaurs that were found during that period is estimated at 2.5 billion dinosaurs.
Public museums contain 32 well-preserved "T-Rex" dinosaurs (Pixabay).
The scarcity of fossils discovered
But these numbers raise an important question: Why did we not find so many fossils and bones of this large group of adult dinosaurs, which were estimated in the billions?
So far, fewer than 100 T-Rex dinosaurs have been discovered, some of which were represented by a single fossil.
There are about 32 adult T-rex dinosaurs that are well preserved in public museums.
Which means we have "one for every 80 million adult dinosaurs that once roamed the Earth," says Marshall.
Marshall believes that these numbers will open the door for debate again.
"These figures will help to estimate the shorter-lived species that have specialized in some geographical areas and that may have been lost from the fossil record," he concludes.