Imagine an almost endless crowd of 2.5 billion Tyrannosaurus Rex, the most feared predators of the age of the dinosaurs, and the bravest man’s legs can be shaken. The number is not just the result of an overactive imagination, however: according to a new calculation, it is the total number of tyrannosaurs that existed during the evolutionary history of the species 68 to 66 million years ago.
It is clear that the number of co-existing T. rex that corresponded to a single generation of these animals was much more modest: about 20,000 animals, spread over an area of North America measuring 2.3 million square kilometers (i.e. more or less a quarter of that of Brazil Territory).
The estimates, contained in the latest issue of the American journal Science, were made by a team from the University of California at Berkeley. Under the direction of Charles Marshall, the work is also signed by the Brazilian biologist Daniel Varajão Latorre, who is currently doing his PhD at Berkeley.
Estimates like this had already been tried in the past, but one of the advantages was the charisma of the tyrannosaurs (12.5 m long hunters whose names adorn boys and girls from all over the world from an early age) and the presence of fossils found in different countries regions of the world are scattered. American territory is the vast amount of data available on the species that has been studied since the early 20th century.
Thanks to that, today’s paleontologists have good clues about movement, bone development, life cycle, and even T. rex metabolism, which makes the accounts a lot easier – at least up to a point.
“We essentially believed that it would be possible to quantify all uncertainties and thus arrive at a robust answer, even if it was within a large margin of error,” concludes Marshall.
“At first glance, the question may seem like a child, this question, how many dinosaurs were there in the world?” In addition to curiosity, there is also an academic justification, as understanding the fossil record is critical to paleontology, ”explains Latorre.
The researchers took into account the major collections of fossils of the species (as a “cut-off note” they chose only those that contained three or more T. rex bones) and generally followed what is known as Damuth’s law. This is a well-known relationship between an animal’s size and population density – in this case, an inverse relationship: the larger the animal, the smaller the number of animals in a given area.
It sounds simple, but the problem is that multiple variables cause the exact relationship to vary greatly from one animal to another, explains Marshall. For example, ecological differences have a certain weight – the account changes if the environment is more or less rich in food or if there is a harsh or mild climate. The numbers also differ if the animal has cold or hot blood (the first type needs more energy and therefore tends to be less common) or depending on how it feeds.
Fossils give a good overview of some of these factors, such as: B. the growth rate (there are good reasons to assume that T. rex reached sexual maturity, for example between 12 and 15 years of age) and the metabolism – the group takes into account It is more likely that the animals had an “almost warm” blood organism, which lies halfway between that of today’s mammals and that of some large reptiles such as the Komodo dragon.
Based on this, they conclude that the animal’s demographic density was about 0.0091 dinosaurs per square kilometer – which would add up to just two T. rex for the entire Washington area, four in Curitiba or 13 animals in the city of Sao Paulo.
The species appears to have survived to the point when a celestial object struck Earth 66 million years ago and wiped out both T. rex and other non-avian dinosaurs (since the group also includes birds descended from small carnivorous dinosaurs) . According to research calculations, only 1 in 80 million individuals of the species have been found by paleontologists to date.
“What impressed me most about the job was how most of our uncertainty was related to what we know about living species rather than what we know about extinct species,” says Latorre.
“This would allow us to learn more about the density and population size of current species, which would even provide important evidence for their conservation. By keeping an eye on population density, you can spot the points where this number is no longer recoverable [para a continuidade da reprodução de uma espécie]and thus close to extinction. “