Data from: Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators

The extinct shark Carcharocles megalodon 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 C. megalodon 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 C. megalodon also displayed this trend, increasing in size over time and reaching its largest size prior to extinction. We found that C. megalodon 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 C. megalodon (i.e., no net changes over time), contrasting with the trends of the megatooth lineage and our hypothesis. Given that C. megalodon 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.

已灭绝的巨齿鲨（Carcharocles megalodon）是地球史上体型最为庞大的海洋顶级捕食者之一。然而学界对其体型随时间与空间的变化规律仍知之甚少。本研究围绕巨齿鲨（C. megalodon）在其演化时间跨度与地理分布范围内的体型变化趋势展开分析，以期深入理解其生态特征与演化历程。鉴于该物种是巨齿鲨类群（megatooth lineage）的最后一员，而该类群被认为存在随时间推移体型持续增大的演化趋势，我们提出假说：巨齿鲨同样遵循这一规律，体型随时间不断增长，并在灭绝前达到峰值。研究结果显示，巨齿鲨的体型分布呈左偏态（left-skewed），暗示长期存在的选择压力更倾向于保留体型更大的个体；同时其体型在地质历史时期存在显著的地理变异，该现象可能源于这种广布性物种所面临的异质化生态约束。进一步分析表明，巨齿鲨的体型演化整体呈现停滞模式（stasis），即长期无净体型变化，这与巨齿鲨类群的演化趋势及我们的假说均不一致。鉴于巨齿鲨是存续时间较长且化石记录分布广泛的物种，本研究借此案例为理解海洋顶级捕食者的体型演化趋势提供了深时视角。例如，本研究结果显示：(1) 掠食性鲨鱼若以更广泛的猎物类群为食，其面临的选择压力或更青睐体型更大的个体，并在地质时间尺度上形成左偏态的体型分布；(2) 广布性海洋顶级捕食者的体型变异或取决于其与地理分隔群落间的相互作用；(3) 鲨鱼物种的内在特性可使其体型在地质历史时期保持稳定，而不受其所在类群的体型演化趋势影响。