Why did the Giant Great White Shark (Carchocles megalodon) Become Extinct?

The giant great white shark (Carchocles megalodon) existed as a species from ~23 million years BP until ~2.6 million years BP, and the evidence suggests this 60 foot monster preyed on whales.  It was 1 of the many marine species to become extinct during the late Pliocene.  Scientists believed megalodon was a warm water species and couldn’t survive cooling ocean waters that resulted from the emergence of the landbridge between North and South America.  However, a brand new study determined climate change could not have been the cause of megalodon’s extinction.

The authors of this study mapped out all of the sites where megalodon fossil teeth have been collected along with all fossil shark collection sites where megalodon remains were absent.  They estimated the range of the species over geologic time. Megalodon, though it originated in tropical waters, later expanded its range to waters that are thought to have been quite cold.  During glacial maximums megalodon’s potential habitat range shrank by a mere 2%, while it expanded by 8% during warmer interglacials.  Most of the area where megalodon lived was not “negatively impacted by climate change.”

Populations of C. megalodon over time. From Pimiento et al., 2016.

Map of megalodon fossil collection sites, dated over geological time periods.  From the below referenced paper.

If climate change didn’t snuff out megalodon, what was the cause of its extinction?  The researchers who published this study suggest 2 possible causes: a reduction in whale species diversity, and competition with other predators.  They note a decline in whale species diversity during the end of the Miocene is correlated with an apparent decrease in megalodon’s range distribution.  This seems a plausible explanation.  Many of megalodon’s favorite prey species went extinct, depriving the giant shark of food that it could efficiently feast upon.  I’m not convinced competition with other predators was a factor in megalodon’s extinction.  An extinct predatory species of sperm whale (Livyatan  melvillei) likely fed upon the same prey species as megalodon.  The ancestors of the modern day great white sharks (Carcharodon hubbeli) and killer whales (Orca sp.), also may have shared the same prey items.  However, megalodon co-existed with these species for millions of years, so I have a hard time accepting this explanation.

Size comparison between megalodon, a killer whale, and a human. A pod of killer whales could’ve rubbed out a single megalodon.  Perhaps this was a factor in their extinction.

skeletal reconstruction Livyatan melvillei by Christopher252

An extinct species of predatory sperm whale–Livyatan melvillei–probably competed with megalodon for the same prey.  

The extinction of megalodon may have  shaped the evolution of baleen whales.  Whales no longer had to be agile fast swimmers to escape megalodon, but instead could grow to a great size that enabled them to store food as blubber.  The stored fat helped baleen whales swim long distances to warmer waters for breeding and calving.  Killer whales, their lone remaining non-human predator, are less common in warmer waters, and whale calves have a greater chance of survival there.

Reference:

Pimiento, Catalina; et. al.

“Geographical Distribution Patterns of Carchocles megalodon over time Reveal Clues about Extinction Mechanisms”

Journal of Biogeography March 2016

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