Archive for Damuth’s Law

how many T-Rex can you fit in your backyard?

Posted in Statistics with tags , , , , , on April 30, 2021 by xi'an

A fascinating question examined in this issue of Science [as pointed out by Nature!] in a paper by Marshall et al. on how many T. Rex(es) roamed the Earth at a given time (in the Cretaceous).  The figure is evaluated from Damuth’s Law and relying on estimates of their body mass (8 tons?), the range of its habitat, the longevity of the species (1.2 million years?), its generation time (18 years?), somewhat surprisingly taking the maximum age (28 years) as the age of the oldest observed fossil.

“We assessed the impact of uncertainties in the data used with Monte Carlo simulations, but these simulations do not accommodate uncertainties that might stem from the choices made in the design of our approach.”

The resulting global evaluation is of an abundance of about 20,000 individuals at a given time, albeit with a 95% confidence interval between 1300 and 328,000 animals, with around 127,000 generations, and a total number of T. rex that ever lived amounting to 2.5 billion animals. Fun exercise, but I am rather reserved at the validity of the evaluation, given the uncertainty and poor data about most terms in the equation.