Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms

Abstract

Aim Given its catastrophic consequences, the extinction of apex predators has long been of interest to modern ecology. Despite major declines, no presentday species of marine apex predator has yet become extinct. Because of their vulnerability, understanding the mechanisms leading to their extinction in the past could provide insight into the natural factors that interact with human threats to drive their loss. We studied the geographical distribution patterns of the extinct macro-predatory shark Carcharocles megalodon in order to elucidate its pathway to extinction.Location World-wide from the Miocene to the Pliocene (c. 23-2.6 Ma).Methods A meta-analysis of C. megalodon occurrence records was performed using the Paleobiology Database as a platform. The data were binned into geological time slices, and the circular home range around each data point was mapped in reconstructions made in GPlates. We then quantitatively assessed the species' geographical range and global abundance over time, and the relationship between distribution and climate.Results The pathway to extinction of C. megalodon probably started in the late Miocene with a decrease in its global abundance. This decrease was then followed by a decline in its geographical range during the Pliocene. Although the extinction of C. megalodon has been attributed to climate change, we found no evidence of direct effects of global temperature. Instead, we found that the collapse in geographical distribution coincided mainly with a drop in the diversity of filter-feeding whales and the appearance of new competitors (large predatory whales and the great white shark).Main conclusions This research represents the first study of the distributional trends of an extinct, cosmopolitan apex predator in deep-time. Our results suggest that biotic factors, and not direct temperature limitations, were probably the primary drivers of the extinction of the largest marine apex predators that ever lived.

Evolutionary pathways toward gigantism in sharks and rays

“…), which is known from the Miocene to the Pliocene (Pimiento and Clements ; Pimiento et al. ). Given the high metabolic demands that it imposes (McNab ), mesothermy is associated with high extinction risk among large bodied species when large prey become scarce (Pimiento et al.…”

“…; Pimiento and Clements ; Pimiento et al. ). Finally, we assigned trait values for maximum total length, trophic level, thermoregulatory mode, and feeding strategy for fossil species based on estimates from the literature (Table ).…”

“…Our results were consistent in light of these alternative phylogenetic positions. We adjusted these placements based on the most likely origination and extinction times of the clade (Table S3; Applegate and Espinosa-Arrubarrena 1996;Pimiento et al 2013;Pimiento and Clements 2014;Pimiento et al 2016). Finally, we assigned trait values for maximum total length, trophic level, thermoregulatory mode, and feeding strategy for fossil species based on estimates from the literature (Table S2).…”

“…The mesothermic pathway to gigantism ultimately resulted in the evolution of the largest marine macropredator to have ever lived, the ß18 m †O. megalodon (Ferrón 2017;Ferrón et al 2017), which is known from the Miocene to the Pliocene (Pimiento and Clements 2014;Pimiento et al 2016). Given the high metabolic demands that it imposes (McNab 2009), mesothermy is associated with high extinction risk among large bodied species when large prey become scarce (Pimiento et al 2017).…”

“…This process may have been influenced or facilitated by the planktonic turnover of the Cretaceous-Paleogene (K-Pg; Tajika et al 2018). Similarly, the ultimate attainment of filter-feeding gigantism could have been a response to the vacant niches left by the extinction of gigantic planktivorous bony fishes at the K-Pg boundary (Friedman et al 2010), and persistent pressure from large predators through the Cenozoic (Lambert et al 2010;Pimiento et al 2016).…”