Body-size trends of the extinct giant shark <i>Carcharocles megalodon</i> : a deep-time perspective on marine apex predators

Abstract

The extinct shark <i>Carcharocles megalodon</i> is one of the largest marine apex predators ever to exist. Nonetheless, little is known about its body-size variations through time and space. Here, we studied the body-size trends of <i>C. megalodon</i> through its temporal and geographic range to better understand its ecology and evolution. Given that this species was the last of the megatooth lineage, a group of species that shows a purported size increase through time, we hypothesized that <i>C. megalodon</i> also displayed this trend, increasing in size over time and reaching its largest size prior to extinction. We found that <i>C. megalodon</i> body-size distribution was left-skewed (suggesting a long-term selective pressure favoring larger individuals), and presented significant geographic variation (possibly as a result of the heterogeneous ecological constraints of this cosmopolitan species) over geologic time. Finally, we found that stasis was the general mode of size evolution of <i>C. megalodon</i> (i.e., no net changes over time), contrasting with the trends of the megatooth lineage and our hypothesis. Given that <i>C. megalodon</i> is a relatively long-lived species with a widely distributed fossil record, we further used this study system to provide a deep-time perspective to the understanding of the body-size trends of marine apex predators. For instance, our results suggest that (1) a selective pressure in predatory sharks for consuming a broader range of prey may favor larger individuals and produce left-skewed distributions on a geologic time scale; (2) body-size variations in cosmopolitan apex marine predators may depend on their interactions with geographically discrete communities; and (3) the inherent characteristics of shark species can produce stable sizes over geologic time, regardless of the size trends of their lineages.