The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific

Robert W Boessenecker; Dana J Ehret; Douglas J Long; Morgan Churchill; Evan Martin; Sarah J Boessenecker

doi:10.7717/peerj.6088

The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific

PeerJ. 2019 Feb 13:7:e6088. doi: 10.7717/peerj.6088. eCollection 2019.

Authors

Robert W Boessenecker^{1

2

3}, Dana J Ehret⁴, Douglas J Long^{5

6}, Morgan Churchill⁷, Evan Martin⁸, Sarah J Boessenecker^{1

2

9}

Affiliations

¹ Department of Geology and Environmental Geosciences, College of Charleston, Charleston, SC, USA.
² Mace Brown Museum of Natural History, College of Charleston, Charleston, SC, USA.
³ Museum of Paleontology, University of California, Berkeley, Berkeley, CA, USA.
⁴ New Jersey State Museum, Trenton, NJ, USA.
⁵ Department of Ichthyology, California Academy of Sciences, San Francisco, CA, USA.
⁶ Department of Biology, St. Mary's College, Moraga, CA, USA.
⁷ Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, WI, USA.
⁸ San Diego Natural History Museum, San Diego, CA, USA.
⁹ School of Museum Studies, University of Leicester, Leicester, UK.

Abstract

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 (∼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.

Keywords: Baja California; California; Extinction; Lamniformes; Miocene; North Pacific; Otodontidae; Otodus; Otodus megalodon; Pliocene.

Grants and funding

No specific grant funding was requested for this study. RW Boessenecker benefited from a University of Otago Doctoral Scholarship during early stages of this research, conducted in 2012–2014. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.