Population sizes of T. rex cannot be precisely estimated

Shai Meiri

doi:10.21425/f5fbg53781

Abstract

Marshall et al. recently estimated population densities, range sizes, instant and cumulative total population sizes for Tyrannosaurus rex with narrow ranges of uncertainly. I revisit the assumptions that led them to these conclusions and show that many of these parameters are associated with much wider margins of error than they estimated. Biogeographic estimates seem to have been especially unrealistic, seriously hampering the effort to calculate population level parameters. I posit that biogeographic and ecological uncertainties make it extremely unlikely to be able to estimate population sizes of long-extinct species.

Highlights

I think that their estimates for densities and population sizes of Tyrannosaurus rex are more precise than the data they used allow and are stated with too narrow intervals
Because shape changed markedly during the ontogeny of T. rex individuals (Hutchinson et al 2011, Carr 2020, Persons et al 2020), both assigning fossils to age groups and the mass reconstructions at each age cohort contain further uncertainty – since few individuals are known from each such cohort
All the factors involved in calculating masses across T. rex ontogeny encapsulate much uncertainty – especially in an animal known only from fossils

Summary

Introduction

Undaunted, Marshall et al (2021) recently estimated the population density, and total population size of Tyrannosaurus rex across their entire range, and at a single point in time but across the duration of the existence of this most charismatic of dinosaurs, calculating the total number of T. rex that have ever lived. I think that their estimates for densities and population sizes of Tyrannosaurus rex are more precise than the data they used allow and are stated with too narrow intervals. To estimate T. rex population size, Marshall et al (2021) estimated its body size, diet, and metabolic rate.

Results

Conclusion