Earth Had 2.5 Billion Tyrannosaurus Rex and Other Revelations

During 2.4 million years of existence on Earth, a total of 2.5 billion Tyrannosaurus rex ever lived, and 20,000 individual animals would have been alive at any moment, according to a new calculation method we described in a paper published on April 15, 2021 in the journal Science.

To estimate population, our team of paleontologists and scientists had to combine the extraordinarily comprehensive existing research on T. rex with an ecological principle that connects population density to body size.

From microscopic growth patterns in bones, researchers inferred that T. rex first mated at around 15 years old. With growth records, scientists can also generate survivorship curves – an estimate of a T. rex’s chances of living to a given age.

Using these two numbers, our team estimated that T. rex generations took 19 years. Finally, T. rex existed as a species for 1.2 to 3.6 million years. With all of this information, we calculate that T. rex existed for 66,000 to 188,000 generations.

From the fossil record alone, we had generated a T. rex turnover rate. If our team could estimate the number of individuals in each generation, we would know how many T. rex ever lived.

In ecology, there is a well-established relationship between body mass and population density called Damuth’s law. Larger animals need more space to survive – one square mile of grassland can support a lot more bunnies than elephants. This relationship is also dependent on metabolism – animals that burn more energy require more space.

Paleontologists have come up with a range of good estimates of T. rex’s body mass and have also estimated its metabolism – slower than mammals but somewhat faster than a large modern lizard, the Komodo dragon. With Damuth’s law, we then estimated that the ancient world held about one T. rex every 42.4 square miles (109.9 square km). That’s about two individuals in the entire area of Washington, D.C.

Now we had all the pieces we needed. Multiplying the population density by the area in which T. rex lived gives us an estimate of 20,000 individuals per generation.

Why It Matters

Once we figured out the average population size, we were able to calculate the fossilization rate for T. rex – the chance that a single skeleton would survive to be discovered by humans 66 million years later. The answer: about 1 in 80 million. That is, for every 80 million adult T. rex, there is only one clearly identifiable specimen in a museum.

This number highlights how incomplete the fossil record is and allows researchers to ask how rare a species could be without disappearing entirely from the fossil record.

Beyond calculating the T. rex fossilization rate, our new method could be used to calculate population size for other extinct species.

What Still Isn’t Known

Estimates about extinct animals always include some amount of uncertainty. Our estimate of T. rex population density ranges from one individual for every 2.7 square miles (7 square km) to one for every 665.7 square miles (1,724 square km). But surprisingly, the largest source of this uncertainty comes from Damuth’s law. There is a lot of variation in modern animals. For example, Arctic foxes and Tasmanian devils have similar body mass, but devils have six times the population density.

Further study of living animals could tighten up our estimates on T. rex.

We also don’t know fossilization rates of other long extinct dinosaurs. If we have many fossils of one species, does that mean they were more common than T. rex, or do we simply recover their fossils more often?

What’s Next

This study might lead to other hidden facts about T. rex biology and ecology.

For instance, we might be able to learn whether T. rex populations fluctuated up and down with Triceratops – similar to wolf and moose predator and prey relationships today. However, most other dinosaurs do not yet have the incredibly rich data from decades of careful fieldwork that allowed our team to tally up T. rex.

If scientists want to apply this powerful technique to other extinct animals, we’ve got some more digging to do.

Ashley Poust is a research associate in Paleontology at University of California, Berkeley

Daniel Varajão de Latorre is a Ph.D. student in Paleontology, University of California, Berkeley

This article was originally published in The Conversation. Read the original article here: https://theconversation.com/how-many-tyrannosaurus-rex-walked-the-earth-159041

Tags:

  • Show Comments (0)

Your email address will not be published. Required fields are marked *

comment *

  • name *

  • email *

  • website *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Ads

You May Also Like

Brazil’s Ecotourism Is The Main Drawing Card for Arab Visitors

The sun and beautiful Brazilian beaches are not the main destinations in the country ...

Don’t Call Me Bitch. Italians Move to Change Synonyms to the Word Woman

Public figures from writers to lawmakers have launched a campaign ahead of International Women’s ...

Brazil Earmarks US$ 23 Billion for Science and Technology

Brazil has just launched a new science plan, aiming to strengthen the role of ...

Brazil’s Plan: Deforestation Zero by 2030

Home to the vast Amazon, Brazil has reduced its deforestation rate by more than ...

Escola de Samba Rosas de Ouro from São Paulo, Brazil

Brazil Carnaval Knows Much About Science Books

Brazil's annual Carnaval earlier this month (from February 16 to 21) played host to ...

Indians, Satellites, Helicopters, Machine Guns: All Is Fair in the War to Defend the Amazon

When George Porto joined Brazil’s environment agency 13 years ago, the country didn’t have ...

A capuchin monkey in Brazil hoists a stone tool to crack open nuts. Luca Antonio Marino, CC BY-ND

A Farm in Brazil Provides a Unique Window on Human Evolution

Human beings used to be defined as “the tool-maker” species. But the uniqueness of ...