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Tyrannosaurus rex

2.5 billion Tyrannosaurus rex – Researchers determine the population density and total number of the most famous predatory dinosaurs

Thinly planted: How many specimens of Tyrannosaurus rex traversed the landscape in the Cretaceous Period? Researchers have now determined this based on the body traits and biology of the predatory dinosaur. The result: about 20,000 adult T.rex representatives live in their area of ​​distribution at the same time – about one out of 110 square kilometers. Predictably, over their entire era, there were about 2.5 billion dinosaurs on Earth.

Tyrannosaurus is the most famous and most researched dinosaur of the Cretaceous period. Thanks to several fossil discoveries, especially from North America, we know that T. rex is constant and graceful It was as well as before Cannibalism Did not flinch. Of its own Skull construction It gave him such a strong sting that he himself Thick bones It can crack easily. The The largest specimens This predatory dinosaur was 13 meters long and weighed nine tons.

Reconstruction of this first type of Tyrannosaurus rex fossil, discovered in 1941, is now in the Carnegie Museum in Pittsburgh. © Scooter Robert Anselmo / CC-by-sa 3.0.0 update

Population density equation

But one question remains unanswered: How many of these giant carnivores were there at that time? This can hardly be determined from the fossil finds, because they represent only a small fraction of the previous stock, and whether or not the specimen was preserved and found is more than just a coincidence. So, a research team led by Charles Marshall Fan at the University of California, Berkeley, looked for a different way to track the number of dinosaurs.

To do this, the researchers used an approach that biologists estimate the population density of animals that live today – Damoth’s law. According to this formula developed by the American ecologist John Damoth, the population density of animal species depends on their body weight, position in the food chain, and physiology.

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The smaller the animal and the slower its metabolism, the longer it can survive permanently in the same space. If the animal is an omnivore and is at the top of its food chain, it also requires more space than a low-feeding herbivore.

Among predatory mammals and the Komodo dragon

Based on this formula and knowledge about Tyrannosaurus rex, the team based its calculations on the following assumptions: The average fully grown T.rex weighed 5.2 tons, but quickly grew larger and was the first predator in its home. Dinosaur physiology is only partially known, but it is believed that it was able to regulate its body temperature, at least in part.

In terms of physiology, Tyrannosaurus probably stood between predatory warm-blooded mammals and cold-blooded carnivorous reptiles such as Komodo dragons. The researchers inserted the corresponding values ​​into Damoth’s formula and were able to determine how many dinosaurs could live in their distribution area at the same time.

Just one T-Rex over an area of ​​110 square kilometers

The result: looking per square kilometer, tyrannosaurs were few and far between: mathematically, there were only about 0.0091 samples per square kilometer – this corresponds to one T-rex per 110 square kilometers or eight in the Berlin area. Compared to today’s predators, the predator dinosaur population was only 16 percent the density of tigers and seven percent the density of lions.

Extrapolating to the entire distribution area of ​​2.3 million square kilometers, about 20,000 dinosaurs lived in the vast expanse of North America in the Cretaceous period at the same time. However, Marshall and his team acknowledge that there are significant doubts due to the approximate physiology of the predatory dinosaur – the range extends from 1,300 to 328,000 specimens found at the same time.

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2.5 billion dinosaurs in total

The number gets significantly larger if you look back at the entire era in which the T-Rex happened. According to fossil records, this species should have existed about 2.4 million years ago – from about 68 million years ago to the end of the dinosaurs about 66 million years ago. Coupled with an average generation time of about 19 years, this means that there could be around 127,000 generations of tyrannosaurs, the researchers report.

That is to say: a total of 2.5 billion dinosaurs could live on Earth during the late Cretaceous period – on average. Due to high suspicion, it would have been 140 million, or as many as 42 billion. “We focused on developing strong boundaries for the variables we need for the computation,” says Marshall. The next step is to refine this and provide the best possible estimate.

Large gaps in the fossil record

After all, the new data also provides preliminary indications of how small the proportion of the total number of dinosaurs found as fossils: “Today there are about 32 relatively well-preserved adult specimens of Tyrannosaurus rex in museums around the world,” Marshall says. Additionally, there are a few dozen fossil finds that consist of one or a few bones. “This means that we only found one T-Rex out of 80 million fossils,” the researcher says.

Even if their calculations are inevitably approximate, they see applying Damuth’s Law to extinct animal species as an opportunity for paleontology: “For example, we can estimate the number of short-lived, geographically specialized species lost in our fossil archives so far,” Marshall says. “With this we begin to define what we do not know yet.” (Science, 2021; Doi: 10.1126 / science.abc8300)

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Coyle: University of California – Berkeley