The Early Pliocene extinction of the mega-toothed shark Otodus megalodon:a view from the eastern North Pacific
The Early Pliocene extinction of the mega-toothed shark Otodus megalodon:a view from the eastern North Pacific
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DOI：
10.7717/peerj.6088
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发表时间：
2019-02-13
期刊：
影响因子：
2.7
通讯作者：
Boessenecker, Sarah J.
中科院分区：
文献类型：
--
作者：
Boessenecker, Robert W.;Ehret, Dana J.;Boessenecker, Sarah J.
已灭绝的巨型鲨鱼巨齿鲨是掠食性巨齿鲨谱系的最后一个成员，几乎所有大陆的新近纪沉积物都有报道。巨齿鲨灭绝的时间被认为是在上新世，尽管更新世牙齿的报道加剧了巨齿鲨可能仍然存在的猜测。耳齿鲨谱系（古新世至上新世）的长寿及其在现代动物群中的明显缺失引出了一个问题：这种巨型鲨鱼何时以及为何灭绝？解决这个问题需要密集采样的海洋脊椎动物化石记录以及强大的地质年代学框架。许多历史上重要的盆地，含有堆积的新近纪海洋脊椎动物化石组合，缺乏经过良好采样和测年的上新世下层和上层地层（例如大西洋沿海平原）。美国加利福尼亚州和墨西哥下加利福尼亚州的化石记录提供了保存在已确定年代的岩石地层序列中的理想组合序列。这项研究回顾了来自北美洲西部后麦西尼亚海相地层的巨齿鲨的所有记录，并评估了它们的可靠性。北太平洋东部所有后赞克雷巨齿鲨的出现都表现出明显的改造证据或缺乏可靠的来源；巨齿鲨最年轻的可靠记录是上新世早期，这表明在上新世早晚期边界（大约 3.6 Ma）灭绝，与日本、北大西洋和地中海最年轻的巨齿鲨出现相对应。这项研究还重新评估了已发布的数据集，彻底审查了每个事件并证明了每个事件的地质年代年龄，并排除了一些可疑的记录。使用最佳线性估计对数据集进行重新分析，得出中位灭绝日期为 3.51 Ma，比之前提出的上新世-更新世灭绝日期（2.6 Ma）稍早。中新世后海洋学的变化和海面温度的降低可能导致了范围的破碎化，而上新世期间与新进化的大白鲨（Carcharodon carcharias）的竞争可能导致了巨齿鲨的灭绝。另外，这些发现也可能表明巨齿鲨在全球范围内异步灭绝。
The extinct giant shark Otodus megalodon is the last member of the predatory megatoothed lineage and is reported from Neogene sediments from nearly all continents. The timing of the extinction of Otodus megalodon is thought to be Pliocene, although reports of Pleistocene teeth fuel speculation that Otodus megalodon may still be extant. The longevity of the Otodus lineage (Paleocene to Pliocene) and its conspicuous absence in the modern fauna begs the question: when and why did this giant shark become extinct? Addressing this question requires a densely sampled marine vertebrate fossil record in concert with a robust geochronologic framework. Many historically important basins with stacked Otodus-bearing Neogene marine vertebrate fossil assemblages lack well-sampled and well-dated lower and upper Pliocene strata (e.g., Atlantic Coastal Plain). The fossil record of California, USA, and Baja California, Mexico, provides such an ideal sequence of assemblages preserved within well-dated lithostratigraphic sequences. This study reviews all records of Otodus megalodon from post-Messinian marine strata from western North America and evaluates their reliability. All post-Zanclean Otodus megalodon occurrences from the eastern North Pacific exhibit clear evidence of reworking or lack reliable provenance; the youngest reliable records of Otodus megalodon are early Pliocene, suggesting an extinction at the early-late Pliocene boundary (similar to 3.6 Ma), corresponding with youngest occurrences of Otodus megalodon in Japan, the North Atlantic, and Mediterranean. This study also reevaluates a published dataset, thoroughly vetting each occurrence and justifying the geochronologic age of each, as well as excluding several dubious records. Reanalysis of the dataset using optimal linear estimation resulted in a median extinction date of 3.51 Ma, somewhat older than a previously proposed Pliocene-Pleistocene extinction date (2.6 Ma). Post-middle Miocene oceanographic changes and cooling sea surface temperature may have resulted in range fragmentation, while alongside competition with the newly evolved great white shark (Carcharodon carcharias) during the Pliocene may have led to the demise of the megatoothed shark. Alternatively, these findings may also suggest a globally asynchronous extinction of Otodus megalodon.