No evidence for Bergmann's rule in Otodus megalodon

Abstract

It has been proposed that Otodus megalodon exhibits a Bergmann‐like size pattern, with individuals growing larger in cooler waters, an interpretation used to challenge the existence of fossil nursery assemblages. Here, we reanalyse the dataset used to support this claim, restricting analyses to upper anterior teeth to control for dental positional effects. We test for temporal stability in body size across the Miocene and Pliocene and evaluate global‐scale correlations between body size and sea‐surface temperature. Using ordinary least squares and linear mixed‐effects models in both frequentist and Bayesian frameworks, we find no statistically significant relationship between temperature and body size. Most regressions yield positive slopes, directly contradicting the negative trend predicted by Bergmann's rule. In contrast, nursery designation explains a substantially greater proportion of body size variation, showing a consistent and significant negative effect across all models. Furthermore, we develop an expanded modelling framework that relates temperature directly to tooth crown height while accounting for jaw and positional heterodonty and explicitly incorporating nursery designation and locality‐level palaeotemperature uncertainty. Results from this approach likewise provide no support for a temperature–size relationship, while reinforcing the dominant influence of nursery assemblages on size variation. We identify conceptual and methodological limitations in the previous study, including biologically implausible size predictions and uncertain palaeotemperature estimates. Overall, our findings refute the proposed temperature–size pattern and support the interpretation of small‐bodied fossil assemblages as juvenile‐dominated nurseries, underscoring the importance of rigorous quantitative testing in macroecological analyses based on fossil data.