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Evolution, diversity, and disparity of the tiger shark lineage Galeocerdo in deep time
Paleobiology ( IF 1.951 ) Pub Date : 2021-03-24 , DOI: 10.1017/pab.2021.6
Julia Türtscher, Faviel A. López-Romero, Patrick L. Jambura, René Kindlimann, David J. Ward, Jürgen Kriwet

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:

虎鲨世系Galeocerdo的进化,多样性和差异性

鲨鱼的化石记录悠久而丰富,由于软骨骨骼矿化程度较差,因此鲨鱼主要由孤立的牙齿组成。代表现代海洋中尖角捕食者的虎鲨(Galeocerdo)具有已知的化石记录,可追溯到始新世(约56 Ma),迄今包括22种已灭绝的物种和一种现存物种。但是,许多化石物种仍存疑问,导致虎鲨属的进化史仍未解决。在这里,我们介绍了Galeocerdo化石记录的修订版通过检查深层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,以进行物种识别。在化石和现存的虎鲨齿上采用这种组合方法,我们的结果仅支持代表有效分类单元的六个物种。此外,差异分析显示多样性和差异不是隐含相关的,并且Galeocerdo自中新世以来,尽管它从4种减少到1种,但仍保留了相对较高的牙齿差异。通过这项研究,我们证明了对孤立的鲨鱼牙齿进行定量几何形态计量学技术和定性形态比较的组合方法,为区分具有高度相似牙齿形态的物种提供了有用的工具。

更新日期:2021-03-24
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