One of the questions that sharks scientists most commonly hear from the general public is "Could Megalodon still be alive!?". I personally love receiving this question because it is a great example of how popular culture has made people interested in learning about sharks. Sadly though, I regret to have to inform these curious enquirers that Meg is, indeed, as dead as the dodo. There are several different theories about what drove these gargantuan predators to die out around 3 million years ago. One such idea is that great white sharks (Carcharodon carcharias) came along and outcompeted Meg into extinction. So could this be true? Were great whites responsible for Megs dying out? And if so, how could this smaller species outcompete one of the largest carnivores that ever lived!?
Meet Meg
The Megalodon (Otodus megalodon (previously known as Carcharocles megalodon)) was an enormous species of predatory shark that lived some 23 to 3 million years ago. One of the largest predators that ever lived, Megalodons could reach incredible sizes of some 16 - 18 metres from nose to tail, and preyed upon fatty whales, dolphins and seals to maintain their great bulk. They boasted multiple rows of serrated teeth - each several inches in length - which were perfect for biting their large prey into bite-sized pieces (Pimiento et al, 2016; Boessenecker et al, 2019; Cooper et al, 2020).
During their reign, Megalodons had a broad distribution - living in tropical, sub-tropical and temperate waters, in every major ocean basin around the world Pimiento et al, 2016).
Rigorous analysis of the fossil record has proven that Megalodon went extinct no later than 3.2 million years ago, but why on Earth did such an incredible, impressive predator die out? (Boessenecker et al, 2019).
A Chilly Climate?
It is thought the pathway to the Megalodons' extinction began during the Late-Miocene period. If we look at the fossil records for this time, we can see a marked decrease in Meg's abundance - with noticeably fewer fossils dating to this period compared to the previous years. A little later on, the fossil record also shows that Meg's distribution contracted significantly during the Pliocene period - with no fossils to be found at all in some regions where we found many in the preceding geological layers (Pimiento et al, 2016).
During the Miocene and Pliocene periods the world was changing... climates were warming and cooling again, currents and sea levels were shifting, seaways were opening and closing as tectonic plates moved - all driving new species of marine animals to evolve (Boessenecker et al, 2019).
As their declining abundance coincided with the climate becoming noticeably warmer during the Miocene and their range contractions correlated with the cooler climate of the Pliocene, scientists have wondered if Megalodons' extinction was caused by ancient climate change. If the climate caused shifts in ocean temperatures, it is possible that this made Meg's habitats too cold. This would have limited the space they could live in or fragmented their habitats so much that they could not breed successfully, eventually driving them to extinction (Pimiento et al, 2016; Boessenecker et al, 2019).
However, scientists have not been able to find any evidence that this is true and, as we are now suspecting that Megalodons had a wider thermal tolerance than we previously thought, some experts now wonder if this is not (or not the only) cause of Meg's extinction (Pimiento et al, 2016a; Boessenecker et al, 2019).
Please, Sir, Can I have Some More?
Another theory about why Megalodon went extinct is that they simply did not have enough to eat. Around the period that we see Megalodons beginning to decline, the fossil record also shows us evidence that marine mammals (whales and dolphins) had shifted their distributions polewards - away from where the Meg was living. What's more, these fossil beds show there was also a marked decline in how many different species of seals and sealions were swimming the oceans at this time. This drastic reduction in prey available to Megalodon could certainly have been a significant factor - if not the major cause - of their extinction (Pimiento et al, 2016; Boessenecker et al, 2019).
Clash of the Titans
Yet, it may not only have been whales that Meg snacked on that aided in their demise... There is also a theory that the rise of large predatory whales may have created enormous competitive pressure for Megalodons. At a similar time during the Miocene period where we see Megalodons were on the decline, macrophagous sperm whales evolved. Reaching a comparable size to the Meg, it is likely these apex predators targeted the same prey and may have even outcompeted Megalodon for their meals. Therefore, they could certainly have been a factor in the extinction of the Megalodon (Boessenecker et al, 2019).
Jaws vs Meg
But there may have been another predator on the block who was also competing with the Megalodon... The great white shark. Ancient ancestors of the great white called Carcharodon hubbelli arose during the Miocene and the white sharks themselves first appeared during the Pliocene. In fact, the time when we first see fossil evidence that white sharks were living all around the world overlaps perfectly with Megalodon's extinction (Pimiento et al, 2016; Boessenecker et al, 2019; McCormack et al, 2022).
Studies of zinc isotope ratios in the tooth enamel of these mega sharks have shown that great white sharks and Megalodons had had a similar diet. Analysis of the changes of these isotopes through time, have shown us that Megalodon occupied increasingly lower "trophic levels" as time progressed during the Pliocene period, where great white occupied increasingly higher levels. This means that great whites were certainly competing with Meg for limited food resources... Based on who is still around today, I think it is safe to say that the white sharks won (McCormack et al, 2022).
The Winner Takes It All
Evolution is a brutal and violent process, with newly evolved species usurping long-standing OGs, as their contemporary adaptations mean they are better suited to the ever-changing environment. Great white sharks, with their smaller body size, agility, thermal tolerance and wide distribution, were simply better adapted to the habitat with limited prey availability as it was during the Pliocene.
Yet, whilst it now seems very likely that the emergence of the mighty great white shark was probably a factor in the decline of the Megalodon, we cannot totally blame them, as it is unlikely that they alone drove the Meg to extinction. In fact, it is more likely that a combination of changing climate, reduced prey availability and competition with newly evolved predators, including both whales and great whites, all came together in a perfect storm that sadly saw an end to the magnificent Megalodon.
To learn more you can check out Size Matters and Myth Busted: Megalodon is DEFINITELY Extinct.
References
Boessenecker RW, Ehret DJ, Long DJ, Churchill M, Martin E & Boessenecker SJ (2019). The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific. PeerJ, 7, e6088. Access online.
Cooper JA, Pimiento C, Ferrón HG (2020). Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction. Scientific Reports, 10, 14596. Access online.
McCormack J, Griffiths ML, Kim SL, Shimada K, Karnes M, Maisch H, Pederzani S, Bourgon N, Jaouen K, Becker MA, Jöns N, Sisma-Ventura G, Straube N, Pollerspöck J, Hublin J-J, Eagle RA & Tütken T (2022). Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes. Nature Communications, 13:1, 2980.
Pimiento C, MacFadden BJ, Clements CF, Varela S, Jaramillo C, Velez‐Juarbe J, & Silliman BR (2016a). Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms. Journal of Biogeography, 43:8, 1645-1655. Access online.
By Sophie A. Maycock for SharkSpeak
