Dinosaur tally research begins with Tyrannosaurus rex per square mile

Research published this week showed a team interested in the total population of individual species of dinosaurs. They began their work with one of the best-known dinosaurs, Tyrannosaurus rex, taking a crack at estimating new metrics based on what they already know to be true. They've used a relationship established between body size and population density in extant species to estimate a new set of traits never before calculated in such a way.

The calculations done for this research were meant to be a starting point for future research. Calculations for population density, overall population count over the known years in which T.rex existed, and so forth – all of this is based on data gathered from fossilized bone. Without a time machine, we can't know everything.

Researchers can, on the other hand, get started on ranges based on the data they have now. UC Berkeley scientists gathered data on T.rex fossils to estimate an as up-to-date set of statistics for the species as possible.

Tyrannosaurus statistics

• Age of sexual maturity: 15.5 years

• Maximum lifespan: around 20 years

• Body mass: Approximately 5,200 kilograms (5.2 tons)

• Body mass after sexual maturity: Approximately 7 tons

• Geographic range: 2.3 million square kilometers

• Total species lifespan: 2.5 million years

• Generations: 127,000

• Standing population size: 20,000 individuals*

* This basically means there were likely around 20-thousand T.rex walking our planet at any given time. Given this data, researchers estimated that during the Cretaceous period in North America, there was around one T.rex every 38.6 square miles.

Sure, they'd be concentrated in some areas more than others, but still – it's likely the T.rex would have been a real concern in your life, had you lived in this area at said time.

Big picture metrics

• Total T.rex population: 2.5 billion

• Potential range for total population: 140 million to 42 billion

This is where it begins to be clear that this is still just the beginning of narrowing down calculations such as these. The potential population range goes from 140 million all the way up to 42 billion.

If we're talking the lowest metric, 140 million T.rex total, we've got a standing population size of around 1300, and an approximate generation span of 17.8 years. That'd also mean that for every surviving fossil scientists have uncovered so far, there were 4.5 million T.rex whose fossils did not survive.

By the highest metric, we've got closer to 1.3 billion T.rex per one fossil found. We've got a generation time of around 20.1 years, a standing population of around 328,000, and a far higher per-square-mile rate. At the high end of estimations, researchers suggest there could've been up to 14 T.rex every 38.6 square miles in North America in the Cretaceous period.

From here, researchers can further perfect the methods with which population metrics are calculated, and further narrow the ranges with which these first results are presented.

To learn more about this research, see the paper Absolute abundance and preservation rate of Tyrannosaurus rex. This paper was authored by Charles R. Marshall et. al. in the scientific publication Science, on the 16th of April, 2021. You can find this article in Science Volume 372, Issue 6539, with code DOI:10.1126/science.abc8300 right this minute.