Boessenecker Robert W, Ehret Dana J, Long Douglas J, Churchill Morgan, Martin Evan, Boessenecker Sarah J
Department of Geology and Environmental Geosciences, College of Charleston, Charleston, SC, USA.
Mace Brown Museum of Natural History, College of Charleston, Charleston, SC, USA.
PeerJ. 2019 Feb 13;7:e6088. doi: 10.7717/peerj.6088. eCollection 2019.
The extinct giant shark 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 is thought to be Pliocene, although reports of Pleistocene teeth fuel speculation that may still be extant. The longevity of the 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 -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 from post-Messinian marine strata from western North America and evaluates their reliability. All post-Zanclean occurrences from the eastern North Pacific exhibit clear evidence of reworking or lack reliable provenance; the youngest reliable records of are early Pliocene, suggesting an extinction at the early-late Pliocene boundary (∼3.6 Ma), corresponding with youngest occurrences of 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 () during the Pliocene may have led to the demise of the megatoothed shark. Alternatively, these findings may also suggest a globally asynchronous extinction of .
已灭绝的巨齿鲨是掠食性巨齿鲨谱系的最后成员，几乎在各大洲的新近纪沉积物中都有发现。巨齿鲨的灭绝时间被认为是上新世，尽管有更新世牙齿的报道引发了关于它可能仍然存在的猜测。巨齿鲨谱系的长寿（从古新世到上新世）以及它在现代动物群中明显缺失，引发了这样一个问题：这种巨型鲨鱼何时以及为何灭绝？要回答这个问题，需要一个密集采样的海洋脊椎动物化石记录，并结合一个强大的地质年代框架。许多具有叠置的新近纪海洋脊椎动物化石组合的历史重要盆地，缺乏采样良好且年代测定准确的上新世下部和上部地层（例如大西洋海岸平原）。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这样一个理想的组合序列，保存在年代测定准确的岩石地层序列中。本研究回顾了北美西部墨西拿阶之后海洋地层中巨齿鲨的所有记录，并评估了它们的可靠性。北太平洋东部赞克尔阶之后的所有巨齿鲨出现情况都有明显的再沉积证据或缺乏可靠的出处；巨齿鲨最可靠的记录是上新世早期，这表明它在上新世早期 - 晚期边界（约360万年前）灭绝，这与日本、北大西洋和地中海地区巨齿鲨的最晚出现时间一致。本研究还重新评估了一个已发表的数据集，对每个出现情况进行了全面审查，并确定了每个的地质年代，同时排除了一些可疑记录。使用最优线性估计对数据集进行重新分析，得出的中位灭绝日期为351万年前，比先前提出的上新世 - 更新世灭绝日期（260万年前）稍早。中新世中期之后的海洋学变化和海表温度下降可能导致了分布范围的碎片化，而上新世期间与新进化的大白鲨（噬人鲨）的竞争可能导致了巨齿鲨的灭绝。或者，这些发现也可能表明巨齿鲨在全球范围内是不同步灭绝的。
