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.

已灭绝的鲨鱼巨齿鲨（Carcharocles megalodon）是迄今存在过的体型最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。本研究通过分析巨齿鲨在其时间与地理分布范围内的体型变化趋势，以深入解析其生态学特征与演化历程。鉴于该物种是巨齿型支系（megatooth lineage）的最后一员，而该支系的类群被认为随时间推移体型逐渐增大，因此我们提出假设：巨齿鲨同样遵循这一演化趋势，即体型随时间不断增长，并在灭绝前达到体型峰值。本研究发现，巨齿鲨的体型分布呈左偏态（提示存在长期的选择压力，倾向于保留体型更大的个体），且在地质历史时期中存在显著的地理差异——这可能源于该广布性物种所面临的异质性生态约束。最终我们发现，巨齿鲨的体型演化整体呈现停滞模式（stasis），即体型随时间无净变化，这与巨齿型支系的演化趋势及我们的初始假设均相悖。鉴于巨齿鲨是存续时间较长且化石记录分布广泛的物种，本研究进一步以此为研究体系，为理解海洋顶级捕食者的体型演化趋势提供了地质深时视角。例如，本研究结果表明：① 掠食性鲨鱼为摄食更广泛的猎物类群所承受的选择压力，可能倾向于选择体型更大的个体，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差异，可能取决于其与地理隔离的群落之间的相互作用；③ 无论所属支系的体型演化趋势如何，鲨鱼物种的固有特征均可使其在地质历史时期维持稳定的体型。