The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific - PubMed (original) (raw)

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

Robert W Boessenecker et al. PeerJ. 2019.

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.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1

Figure 1. Map of California and Baja California showing genuine late Miocene and Early Pliocene records of Otodus megalodon, and dubious Late Pliocene and Pleistocene records.

Figure 2

Figure 2. Otodus megalodon teeth from the Capistrano Formation.

SDNHM 53167 in lingual (A) and labial (B) view; LACM 129982 in lingual (C) and labial (D) view; LACM 59837 in lingual (E) and labial (F) view; LACM 115989 in lingual (G) and labial (H) view; LACM 59836 in lingual (I) and labial (J) view.

Figure 3

Figure 3. Otodus megalodon teeth from the Fernando Formation.

LACM 148312 in lingual (A) and labial (B) view; LACM 148311 in lingual (C) and labial (D) view.

Figure 4

Figure 4. Otodus megalodon tooth from the Niguel Formation.

LACM 59065 in lingual (A) and labial (B) view.

Figure 5

Figure 5. Otodus megalodon tooth from the Purisima Formation.

UCMP 219502 in lingual (A) and labial (B) view.

Figure 6

Figure 6. Otodus megalodon teeth from the San Diego Formation.

SDNHM 29742 in lingual (A) and labial (B) view; LACM 156334 in lingual (C) and labial (D) view; LACM 10152 in lingual (E) and labial (F) view; LACM 103448 in lingual (G) and labial (H) view.

Figure 7

Figure 7. Otodus megalodon teeth from the San Mateo Formation.

LACM 131149 in lingual (A) and labial (B) view; SDNHM 24448 in lingual (C) and labial (D) view; SDNHM 23959 in lingual (E) and labial (F) view; SDNHM 77343 in lingual (G) and labial (H) view; SDNHM 23959 in lingual (I) and labial (J) view; SDNHM 23959 in lingual (K) and labial (L) view; SDNHM 23959 in lingual (M) and labial (N) view.

Figure 8

Figure 8. Otodus megalodon teeth from the Tirabuzón Formation.

LACM 29067 in lingual (A) and labial (B) view; LACM 29064 in lingual (C) and labial (D) view; LACM 29077 in lingual (E) and labial (F) view; LACM 29076 in lingual (G) and labial (H) view; LACM 29065 in lingual (I) and labial (J) view; LACM 29074 in lingual (K) and labial (L) view; LACM 29069 in lingual (M) and labial (N) view; LACM 29073 in lingual (O) and labial (P) view; LACM 29075 in lingual (Q) and labial (R) view; LACM 29072 in lingual (S) and labial (T) view.

Figure 9

Figure 9. Inferred dates of extinction for Otodus megalodon using the Optimal Linear Estimation (OLE) model.

Data binned by 10,000 year increments. The histogram (blue) represents the % frequency of a given date that was estimated for the extinction out of 10,000 simulations. The curve (orange) represents increasing cumulative probability that Otodus megalodon was extinct at the given date.

Figure 10

Figure 10. Otodus megalodon teeth of purported Pleistocene age.

LACM 159028 in lingual (A) and labial (B) view, supposedly from Palos Verdes Sand; LACM 10141 in lingual (C) and labial (D) view, supposedly from unnamed strata at Newport Bay Mesa.

Figure 11

Figure 11. Geochronologic age range of _Otodus megalodon_-bearing strata and occurrences in the eastern North Pacific.

Age control of latest Miocene and Pliocene _Otodus megalodon_-bearing stratigraphic units represented by thick vertical gray bars. Stratigraphic range of autochthonous and parautochthonous Otodus megalodon occurrences (allochthonous records excluded) depicted as thin vertical black bars. Abbreviations: NALMA, North American Land Mammal Age.

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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.

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