Sharks (Selachimorpha) are iconic marine predators that have survived multiple mass extinctions over geologic time. Their prolific fossil record is represented mainly by isolated shed teeth, which provide the basis for reconstructing deep time diversity changes affecting different selachimorph clades. By contrast, corresponding shifts in shark ecology, as measured through morphological disparity, have received comparatively limited analytical attention. Here, we use a geometric morphometric approach to comprehensively examine tooth morphologies in multiple shark lineages traversing the catastrophic end-Cretaceous mass extinction-this event terminated the Mesozoic Era 66 million years ago. Our results show that selachimorphs maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous-Paleogene interval. Nevertheless, selective extinctions did impact apex predator species characterized by triangular blade-like teeth. This is particularly evident among lamniforms, which included the dominant Cretaceous anacoracids. Conversely, other groups, such as carcharhiniforms and orectolobiforms, experienced disparity modifications, while heterodontiforms, hexanchiforms, squaliforms, squatiniforms, and †synechodontiforms were not overtly affected. Finally, while some lamniform lineages disappeared, others underwent postextinction disparity increases, especially odontaspidids, which are typified by narrow-cusped teeth adapted for feeding on fishes. Notably, this increase coincides with the early Paleogene radiation of teleosts as a possible prey source, and the geographic relocation of disparity sampling "hotspots," perhaps indicating a regionally disjunct extinction recovery. Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks.

中文翻译：

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牙齿形态阐明了白垩纪末大规模灭绝期间鲨鱼的进化。

鲨鱼（Selachimorpha）是标志性的海洋掠食者，在地质时期的多次大规模灭绝中幸存下来。它们丰富的化石记录主要以孤立的脱落牙齿为代表，这为重建影响不同鲨鱼进化枝的深层时间多样性变化提供了基础。相比之下，通过形态差异来衡量的鲨鱼生态的相应变化受到的分析关注相对有限。在这里，我们使用几何形态测量方法来全面检查多个鲨鱼谱系的牙齿形态，这些鲨鱼谱系经历了灾难性的白垩纪末大规模灭绝——这一事件结束了 6600 万年前的中生代时代。我们的研究结果表明，在整个白垩纪-古近纪期间，鲨类动物的大多数组成分支都保持了几乎静态的牙齿差异水平。尽管如此，选择性灭绝确实影响了以三角形刀片状牙齿为特征的顶级捕食者物种。这在lamniforms中尤其明显，其中包括主要的白垩纪anacoracids。相反，其他类群，如真齿目和直齿目，经历了视差改变，而异齿目、六齿目、角齿目、squatiniforms 和 †synechodontiforms 则没有受到明显影响。最后，虽然一些层状谱系消失了，但其他谱系在灭绝后经历了差异的增加，特别是齿蜘蛛，其特征是适合以鱼类为食的窄尖齿。值得注意的是，这种增加与硬骨鱼作为可能的猎物来源的古近纪早期辐射以及差异采样“热点”的地理重新定位相一致，这可能表明区域上不连续的灭绝恢复。最终，我们的研究揭示了白垩纪末大规模灭绝的复杂形态反应，并强调了影响现代鲨鱼进化的事件。