With what precision can the population size of Tyrannosaurus rex be estimated? A reply to Meiri

Abstract

Interested in the absolute preservation rate of one of the best understood dinosaurs, Tyrannosaurus rex, Marshall et al. (2021) estimated the total number that ever lived. This required estimating its geographic range, longevity, and population density, which required estimating its body mass and physiology. Meiri (2021) questions the precision of our estimates, emphasizing the difficulties in estimating population densities and geographic ranges for living species, and in error propagation. He posits that estimating population sizes of extinct species is ‘extremely unlikely’. While we agree that we did not quantify some sources of uncertainty (for example, in the physiology of T. rex), our calculations do not depend on short-term changes in population density and geographic range, but rather on their long-term averages, rendering many of Meiri’s (2021) concerns moot. We also note that Monte Carlo Simulation propagates uncertainties robustly. That is, we feel we have, in fact, developed a general method for estimating population sizes for extinct species, regardless of any shortfalls in implementation.