The extinct sharkCarcharocles megalodonis 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 ofC. megalodonthrough 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 thatC. megalodonalso displayed this trend, increasing in size over time and reaching its largest size prior to extinction. We found thatC. megalodonbody-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 ofC. megalodon(i.e., no net changes over time), contrasting with the trends of the megatooth lineage and our hypothesis. Given thatC. megalodonis 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.

中文翻译：

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已灭绝巨鲨Carcharocles megalodon的体型趋势：对海洋顶级捕食者的深度观察

灭绝的鲨鱼巨齿鲨是有史以来最大的海洋顶级掠食者之一。尽管如此，人们对其体型在时间和空间上的变化知之甚少。在这里，我们研究了体型趋势C. 巨齿鲨通过其时间和地理范围，以更好地了解其生态和演变。鉴于这个物种是最后一个巨齿谱系，一组显示出据称随着时间的推移而增大的物种，我们假设C. 巨齿鲨也显示出这种趋势，随着时间的推移尺寸增加并在灭绝前达到最大尺寸。我们发现C. 巨齿鲨体型分布是左偏的（表明长期的选择压力有利于较大的个体），并且随着地质时间的推移呈现出显着的地理差异（可能是由于这种世界性物种的异质生态限制的结果）。最后，我们发现停滞是规模演化的一般模式C. 巨齿鲨（即，随着时间的推移没有净变化），与巨牙谱系的趋势和我们的假设形成鲜明对比。鉴于C. 巨齿鲨是一种相对长寿的物种，具有广泛分布的化石记录，我们进一步利用该研究系统为了解海洋顶端捕食者的体型趋势提供了一个深度视角。例如，我们的研究结果表明：（1）捕食性鲨鱼对更广泛的猎物的选择压力可能有利于更大的个体，并在地质时间尺度上产生左偏分布；(2) 世界性顶级海洋捕食者的体型变化可能取决于它们与地理上离散群落的相互作用；(3) 鲨鱼物种的固有特征可以在地质时期产生稳定的大小，而不管其谱系的大小趋势如何。