Paleontologists at the University of California, Berkeley, set out to provide a number about the number of T. rex that lived during the Cretaceous – about 65 million to 98 million years ago – knowing that it would be no easy task.
Fossils have long been used to deepen our understanding of extinct creatures such as dinosaurs, but experts say using these remains to calculate population density and abundance can be challenging.
“There is simply no information to make the estimate,” explains Charles Marshall, director of the University of California Museum of Paleontology, who was part of the research team. “If you find an Easter egg in your garden, how can you estimate how many Easter eggs have ever existed? It just won’t work. You need information from elsewhere – for example, the density of Easter eggs, the area where eggs can be found, and so on. how many years have Easter eggs been placed in gardens. “
“Previously, researchers have tried to estimate things like the likely size of the Tyrannosaurus in its home range and its basic energetic needs, so this is a nice extension of previous work, and it contains a lot of updated information about Tyrannosaurus,” said Nizar Ibrahim, paleontologist at the University of Portsmouth (UK) and National Geographic Explorer, which were not part of the study.
“We just have to keep in mind that all of these intriguing studies involve a certain amount of uncertainty – there’s so much we still don’t know about dinosaurs, even a Hollywood star like T. rex,” added Ibrahim. an e-mail.
20,000 T. rex in North America at a time
Using the fossil record, density data, and climate model data, the UC Berkeley team calculated that about 20,000 adult T. rex, living across North America, likely once existed. This, the researchers say in a study published in the journal Science, means that about 2.5 billion of the predators lived and died during the roughly 2.5 million years the dinosaurs lived.
For the first time, the team also calculated the dinosaur’s lifespan: based on scientific literature and expert opinion, they estimated that a T. rex’s likely age of sexual maturity was 15.5 years, and that its lifespan could be reach to the late 1920s. The dinosaur’s average adult body weight was about 5,200 kg (11,464 pounds), and a growth spurt at sexual maturity could send them to 7,000 kg (15,432 pounds).
Based on these estimates, the team concluded that each generation of T. rex lasts about 19 years, with one dinosaur for every 100 square kilometers (38.6 miles).
With a permanent population of 20,000 dinosaurs, and with some 127,000 generations of the species, there would be a total of 2.5 billion dinosaurs, the team found.
The researchers’ methods “appear to be very informative, while also showing the current limits of what can be done with what we now know,” said Jason C. Poole, chief fossil preparer at the Bighorn Basin Paleontological Institute and a researcher. paleontological artist, who was not. part of the study.
“I’m sure it will open doors to focus even better on the questions of population density and what that means over time,” Poole added in an email. “So this could really help understand things like change in a species over time in relation to evolution and changing ecosystems.”
The study authors estimated that the population density of the species was equivalent to 3,800 of the carnivorous dinosaurs in an area the size of California – but only two in an area the size of Washington DC.
T. rex fossils are rare
Meanwhile, the results also allowed the report’s authors to determine that only about 1 in 80 million T. rex has survived as fossil remains.
“The big impact of this study may be that it shows how rare fossils are, because they represent only a small fraction of the individual organisms that existed, not to mention the depth of time, such as how much happens in a a few thousand to a million years, ”Poole said.
“In some ways this has been a paleontological exercise in how much we can know and how we know,” said Marshall, a co-author of the study and professor of integrative biology and of the Earth and planetary science at UC Berkeley, in a statement. .
“It’s surprising how much we actually know about these dinosaurs and, from that, how much more we can calculate. integrate the many known fossils, ”he said.
Beyond the T. rex
Ibrahim sees other possibilities that arise from this research.
“There are many things we don’t know about the physiology, behavior and food ecology of Tyrannosaurus, but this study offers an interesting approach to estimate the quantity and conservation of dinosaurs,” he said.
“I would like it to be applied to other dinosaurs known from abundant fossils. If we look at a wider range of dinosaurs – predators and prey – we might be able to compare more closely to those of modern dinosaurs.”
“But we’re only scratching the surface, and even with this intriguing study, there’s still a long way to go before we can confidently apply such approaches more broadly to the study of dinosaurs.”