How many “Tyrannosaurus rex” went to Earth?

Research Brief is a short presentation about interesting academic work.

Great idea

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

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

From microscopic models of bone growth, the researchers deduced this T. rex first mating at about 15 years of age. With growth records, scientists can also generate survival curves – an estimate of T. rexChances of living at a certain age. Using these two numbers, our team estimated this T. rex generations lasted 19 years. In the end, T. rex existed as a species from 1.2 to 3.6 million years ago. With all this information, we calculate it T. rex there were between 66,000 and 188,000 generations.

Only from the fossil record did I generate 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 – a square kilometer of grassland can support far more rabbits than elephants. This relationship is also dependent on metabolism – animals that burn more energy require more space.

Paleontologists have come up with a number of good estimates of T. rexbody mass and estimated their metabolism – slower than mammals, but slightly faster than a large modern lizard, the dragon Komodo. With Damuth’s law, I then estimated that the ancient world had about one T. rex every 109.4 square kilometers. These are two individuals from all over Washington, DC

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

Why does it matter

Once we discovered the average population size, we were able to calculate the fossilization rate for T. rex – the chance that a single skeleton will survive to be discovered by humans 66 million years later. The answer: about 1 in 80 million. That is, for every 80 million adults 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 the calculation T. rex fossilization rate, our new method could be used to calculate the size of the population for other extinct species.

What is not yet known

Estimates of missing animals always include some uncertainty. Our estimate of T. rex the population density varies from one individual for every 7 square kilometers to one for every 1,724 square kilometers. But, surprisingly, the greatest source of this uncertainty comes from Damuth’s law. There are many variations in modern animals. For example, arctic foxes and Tasmanian devils have a similar body mass, but devils have six times the population density.

Further study of live animals could strengthen our estimates T. rex.

We also do not know the fossilization rates of other long-extinct dinosaurs. If we have many fossils of a species, it means that they were more common than T. rexor do we simply recover their fossils more often?

What’s next

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

For example, we could find out if T. rex populations fluctuated up and down with Triceratops – similar to today’s prey and wolf and moose relationships. However, most other dinosaurs do not yet have the incredibly rich data from decades of careful fieldwork that allowed our team to match. T. rex.

If scientists want to apply this powerful technique to other extinct animals, we still have some digging to do.