Sharks have a long and rich fossil record that consists predominantly of isolated teeth due to the poorly mineralized cartilaginous skeleton. Tiger sharks (Galeocerdo), which represent apex predators in modern oceans, have a known fossil record extending back into the early Eocene (ca. 56 Ma) and comprise 22 recognized extinct and one extant species to date. However, many of the fossil species remain dubious, resulting in a still unresolved evolutionary history of the tiger shark genus. Here, we present a revision of the fossil record of Galeocerdo by examining the morphological diversity and disparity of teeth in deep time. We use landmark-based geometric morphometrics to quantify tooth shapes and qualitative morphological characters for species discrimination. Employing this combined approach on fossil and extant tiger shark teeth, our results only support six species to represent valid taxa. Furthermore, the disparity analysis revealed that diversity and disparity are not implicitly correlated and that Galeocerdo retained a relatively high dental disparity since the Miocene despite its decrease from four to one species. With this study, we demonstrate that the combined approach of quantitative geometric morphometric techniques and qualitative morphological comparisons on isolated shark teeth provides a useful tool to distinguish between species with highly similar tooth morphologies.

中文翻译：

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虎鲨谱系 Galeocerdo 的进化、多样性和差异

鲨鱼有着悠久而丰富的化石记录，由于软骨骨骼矿化不良，主要由孤立的牙齿组成。虎鲨 (伽利奥塞尔多)，它们代表现代海洋中的顶级捕食者，有一个已知的化石记录，可以追溯到始新世早期（约 56 Ma），包括 22 个公认的灭绝物种和迄今为止的一个现存物种。然而，许多化石物种仍然存在疑问，导致虎鲨属的进化史仍未解决。在这里，我们提出了对化石记录的修订伽利奥塞尔多通过深入研究牙齿的形态多样性和差异。我们使用基于地标的几何形态计量学来量化牙齿形状和定性形态特征以进行物种歧视。对化石和现存的虎鲨牙齿采用这种组合方法，我们的结果仅支持六个物种代表有效的分类群。此外，差异分析表明，多样性和差异并不隐含相关，并且伽利奥塞尔多自中新世以来，尽管其从四个物种减少到一个物种，但仍保持着相对较高的牙齿差异。通过这项研究，我们证明了定量几何形态测量技术和定性形态比较对孤立鲨鱼牙齿的组合方法为区分具有高度相似牙齿形态的物种提供了有用的工具。