The Megalodon: "Mega-deadly food obsession"

Imagine a shark the size of a modern Humpback whale. Now, imagine it with a mouth so large it could swallow you whole. It was a specialist, predating large marine mammals (small - medium sized whales) that frolicked in the ocean between 15.9 – 3.51 million years ago.

I work in a field where I frequently answer the same questions about the largest shark that ever existed...  

“Is the Megalodon, the 15-18 metre long, 50 metric tonne shark... still alive?”

 NO. No. NO. NOOOOOOOOOOO. 

According to a new study, (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) the revised estimates for the disappearance of Otodus megalodon have been pushed back by almost one million years. This gigantic shark was originally though to have died out 2.6 million years ago (at the border of the Pliocene/Pleistocene) but due to erroneous/unreliable reports and reworked material, the estimate is most likely 3.51 million years ago and they were almost certainly gone by 3.2 million. The authors of this study list a number of plausible causes; all of which are highly contentious and equally as dope. 

Computer generated fun! This image is NOT REAL... Image via the Discovery Channel

It's going to be a looooong post but before I begin, some of you may inevitably ask me about the Discovery Channel's 2014 docu-fiction “Megalodon: The Monster Shark Lives”. It’s all absolute bull-shit, every... single... word... It attempted to present fiction as non-fiction in this documentary and as a palaeontologist; I find this docu-fiction absolutely abhorrent. It attracted 4.8 million viewers upon release and with its “Ancient Aliens”, and “Mermaids: The Body Found” lineup of deliberately formatted fake news, this network has lost every ounce of credibility it once had. 

So lets start right at the beginning. 

How did O. megalodon evolve into the biggest shark of all time?

The phylogenetic relationship of O. megalodon and its basal precursors has been up for debate and is still incredibly messy. Considering that we primarily use teeth for this evidence, it makes it very difficult to ascertain speciation. At one stage, Great Whites were considered living descendants of the "Meg", but now we suspect that this macro-raptorial shark belongs to a group known as the Otodontidae that originated within the late Cretaceous, 115 million years ago (despite this, the scientific name Carcharocles megalodon is still widely accepted). But we’ll be focusing on what appears to be the most archaic ancestor of this mega-toothed lineage, the ~55-50 (and possibly up to 45) million year old species Otodus obliquus. 

The age range of all these sharks in these posts is AN ABSOLUTE MESS HOLY HELL IS IT DIFFICULT TO DETERMINE AHHHH... Image via “Red-1-store” on E-bay of a lower O. obliquus tooth.

Otodus obliquus

If you have ever bought a fossil shark tooth, chances are that it belongs to Otodus obliquus, a lamnoid shark that reached up to a possible 9 metres in length. Numerous fossils have been found worldwide from this cosmopolitan species from Asia, Europe, North America, Japan, but especially Morocco in the highly fossiliferous phosphate mines of the Oued Zem. Most of these Moroccan teeth do not have any serrations along the blade (as is evidenced in Megalodon teeth) but other teeth found in a number of localities (ie; the Eocene locality of the Potomac river, Maryland, USA and the Ypres clay of Belgium) have these slight serrations and appear to be evidence of a worldwide transitional event. Serrations evolve to cope with tough flesh... (imagine a steak knife cleaving its way through a piece of beef). 

Why are palaeo-artists afraid of drawing male sharks? Unknown artist. Message me if you know!

It’s hard to figure out exactly what Otodus obliquus was eating, but we know that it couldn’t have initially been the whales; these animals were only just walking back into freshwater habitats ~50 million years ago and it would take 3-5 million years until they reached saltwater. These serrations may have been an adaptation to eating large bodied fish (such as tuna) but would prove vital to existence of these “mega-toothed” sharks, as they would soon begin their “love affair” with whales. 

Next up, the Late Eocene aged Otodus auriculatus.

Triangle of death. Photo via “Prehistoria Florida” on the fossilforum.com 

Otodus auriculatus

Otodus auriculatus was probably one of the largest sharks from ~45 million years ago, up until the early Oligocene (34-30 million years ago). It has teeth over 11 centimetres in size (over 4 inches!). They are characterised by their bulbous roots, coarse serrations and ragged lateral cusplets on the blade of the tooth (which will eventually disappear in younger "Megalodon" teeth). This shark was probably eating the very first seafaring cetaceans and possibly sirenians (dugong relatives); evidence can be found throughout the fossil record. It would eventually give way to the enigmatic Otodus angustidens, the main predatory shark of the Oligocene… 

Pyramid of death. Image via Museums Victoria

Otodus angustidens

O. angustidens was a 9 metre long mega-toothed shark of the Oligocene (34 – 23 million years ago). This epoch straddles a significant period in cetacean evolution, whereby the main groupings of modern whales (the baleen bearing Mysticetes and the toothed Odontocetes) are beginning to evolve. As a result of this, these “Angy” teeth superficially look like serrated triangular daggers, with prominent lateral cusplets. 

"Just try to ignore the continental super-predator Margaret... they're real weird" the mother O. angustidens said to her daughter... Image via Peter Trussler.

The “Angy” is thought to be last of these mega-toothed sharks to have prominent serrated cusplets in the blade of their 4-inch teeth; we begin to see a trend whereby latter species (of the Otodus lineage) lose these cusplets entirely. 

Fun fact: The most complete specimen ever found comes from New Zealand, with a jaw dropping 165 associated teeth and 32 vertebral centra. 

Next up: Otodus chubutensis...  

4 inches of death. Image via buriedtreasurefossils.com 

 Otodus chubutensis

The “Glorious shark of Chubut” is found throughout the early - mid Miocene and disappears during the absolute dominance of the Megalodon (~7-10 million years ago?). This monster shark, possibly 10 metres in length, has teeth more than 4 inches long and has lateral cusplets that are significantly smaller than in O. angustidens. It is possible that the loss of these cusps was driven by a functional demand placed on Otodus teeth to become more efficient in cutting vs. puncturing. The loss of lateral cusplets allowed the tooth to present a longer continuous serrated blade for cutting into their prey; the baleen whales (which were reaching sizes between 4-12 metres in length).

The next phase in this evolution culminates with the largest of these mega-toothed sharks... the one and only Megalodon. 

But what have we found of the "Megalodon" in the fossil record?...  

Jimmy (far left) remembers that he left his car in a permit zone... He did not have his permit on display. Image via Geology and Paleontology of the Lee Creek Mine, North Carolina, III, Bohaska and Ray 2001

Fossil Record

Fossils of the Megalodon are comparatively widespread all over the globe and are represented by a hoard of teeth, a few sparse dinner-plate sized vertebrae, a number of sizeable coprolites (fossilised poop) and traces of feeding damage in the bones of primarily small but some medium sized whales (<12 metres long) and some seals. The skeleton of this shark is made primarily of cartilage and this material does not readily fossilise in the fossil record, especially in marine deposits. But if you want to understand the reason any animal goes extinct, you have to understand what it eats... 

Prey

The Megalodon and its prey matter, smaller baleen whales (and possibly a few Odontocetes, larger bodied seals and sirenians such as dugongs and manatees), arguably represent one of the biggest predator-prey relationships of all time. These whales were no-where near as big as modern varieties (the modern Blue Whale is the largest animal ever, at over 30 metres in length) but even small ones (such as the Cetotheriidae) were still 6 metres in size. Their skull is bigger than you... 

If you look closely at the red and black shirt, it never stops moving. Two continental super-predators (Homo sapiens sapiens) pose with a Pygmy Right Whale. Image by Rodney Start.

They included the Herpetecines (a variety of Cetotheriids), small Balaenids (Right whales) and some smaller Balaenopterids (similar in appearance to blues and humpbacks). But at around 3-3.5 million years ago, dramatic periods of glacial formation (the prolonged "Ice Ages") in the Arctic (and to a smaller extent in the Antarctic - glaciation had occurred on the continent since the mid-late Eocene). For these whales, it established gigantism (>12 meters) as the dominant baleen whale size, something that may have been too big, even for the Megalodon. But this is an incredibly complicated situation; despite the arrival of modern and giant genera in the mid-late Pliocene, most smaller baleen whales persisted. Many taxa survived past the purported 3.51 my extinction date of the Megalodon. There is even a cetotheriid alive today (depending on who you talk to; the modern Pygmy Right Whale is thought to belong to this "archaic" grouping) and is by far one of the most mysterious of the modern Mysticetes. So why did the Megalodon die out? There are a number of factors to consider when discussing the extinction of this macro-predatory fish. 

How did the "Meg" die out?

"DAVID ARE YOU OKAY?!?!"... David the Pygmy Right whale would not be okay... Image via Darryl Wilson.

1) Geographical Barriers and not enough "small" baleen whales

Geographical barriers (such as the closing of Panama seaway) would have hampered taxon dispersal, allowing more cosmopolitan baleen whale species to outcompete other more restricted species. This trend towards larger body size in Mysticetes would have had some kind of effect on the Megalodon, as it most likely struggled to find the "right kind" of smaller sized whale it had depended upon for millennia. There's no doubt these "smaller" whales were there, but the timing is uncanny. This theory makes a-lot of sense and could have allowed populations of the Megalodon to have become fragmented over time, leading to a reduced geographic range. 

 "HARRY ARE YOU OKAY?!?"... Harry the partially dissected Porbeagle was clearly dead. It was at this point the researchers agreed to stop taking their "magic" brownies. Via the Canadian Shark Research Lab.

2) The Cold

All sharks acquire fat in the form of squalene in their liver (which can comprise more than a third of their body length), whereas mammals (such as whales) can use their fat as blubber to insulate them against the biting cold of the Artic/Antarctic. It's possible that the Megalodon could not follow these baleen whale migratory routes as the earth began fluctuating into colder periods at around the mid Pliocene and was forced into warmer areas devoid of prey, as its "fat" could not sufficiently warm its undoubtedly warm-blooded metabolism (modern Great Whites do not migrate far south/north due to this extreme cold, even though food is highly plentiful).

Check out the dentition! With teeth reduced to nubs, this was a killer whale that fed on the rough skin of sharks. Image via Gemma Aboe.

3) Killer whales

One of these theories concern competition. At the end of the Pliocene, the first Orcas appear in the fossil record. It’s possible that an archaic form of Killer Whales outcompeted the Megalodon as the dominant apex predator in the ocean. This theory has a few issues however; the oldest currently known killer whale (in the fossil record) is the late Pliocene Orcinus citoniensis, and its functional morphology does not seem to imply a macrophageous predator. Remains indicate a much smaller animal (of a four metre size) but this should not rule them out altogether; the fossil record is patchy at best and hugely biased... Modern odontocetes have only one set of teeth their entire life, whereas some shark species are estimated to lose anywhere between 10-15,000 teeth in a single lifetime. This leaves a "glut" of shark teeth in the fossil record when compared to any mammal...

The creator of this blog holds his 5.2 million year old baby in his hands. This giant yam is actually a tooth of a macro-raptorial sperm whale. 

4) Killer Sperm whales

By the mid Miocene, giant physeteroids dominated the globe. First named in 2010, Livyatan and its associated kin would have had a monstrous influence on the mid Miocene - early Pliocene environment. This was a sperm whale with 40 teeth the size of a 1.25 litre Coke bottle, a skull the size of a small car and approaching sizes between 13.5 - 17.5 metres in length. Some palaeontologists (in personal discussion) have even suggested that this was a predator that was capable of feasting on the Megalodon...


Why do they think this?


Because of the modern interaction between Orcas and Great Whites. Orcas eat Great Whites. It's worth noting that Orcas (on average) weigh at least a couple more tonnes than a Great white and are at least, a few metres longer. This is a huge advantage to the oceanic dolphin. Whether these giant physeteroids of the Mio-Pliocene were reaching sizes that were larger than the Megalodon is still hotly debated, but there has been very little work done on these macro-raptorial whales in terms of upper size limits. This is a "watch this space" moment throughout the next decade, as more discoveries are made, size estimates will vary as well. I'm putting my money on the fact that Livyatan and it's associated kin were the largest macro-predators of all time, at least in terms of weight... 


But there is a huge issue with this theory, namely the fact that these two gigantic mega-predators co-existed for millions of years with one another (just as Great Whites and Orcas do today). This theory is therefore unlikely, but so awesome to ponder...

Did a space fart kill off the Megalodon? Image via University of Kansas.

5) Super-novas. 

This is an annoying theory, but it's (UNFORTUNATELY) worth mentioning. The Meg was once considered to have gone extinct at the Pliocene/Pleistocene boundary, roughly 2.6 million years ago. It coincided with a supposed marine megafaunal extinction that was only identified in 2017, where at least 30% of marine megafauna died out. Some writers have argued that this occurred because of some bullshit happening in the sky. Apparently there is a well-documented supernova at approximately about 2.6 Ma. This supernova coated the earth in "Muon" radiation, which is apparently harmful to mega-chunky animals, especially along the coastline.This could have killed off these "smaller" baleen whales sticking to the coast, a food source the Meg relied upon.


In short, it's evidence of a supernova at the same time of the Pliocene/Pleistocene mass extinction. That's basically all we can really say about this. This event is (thankfully) no longer applicable to the Megalodon extinction event...

The evolution of this massive macro-predator (the Great White) has not been well understood. For the longest time, people thought it was in some way related to the Meg, but this does not appear to be the case. Enter to the stage, the associated remains of Carcharodon hubbelli, UF 226255. This spectacular 6-8 million year old specimen contains an articulated dentition of 222 teeth, 45 vertebrae and portions of the actual left and right jaw cartilage! It’s with this specimen that we’ve been able to elucidate the origin of the Great White Shark. This mostly complete specimen of Carcharodon hubbelli demonstrates an “evolutionary mosaic” of Great White ancestors, specifically referring to the seven metre long broad toothed mako, Carcharodon hastalis (also known as Isurus hastalis). These teeth are found in abundance throughout the Miocene (especially in Southern Australia). Although C. hastalis does not have any serrations on the blade of the tooth, the other elements of the tooth, specifically the shape of the root, indicate a close evolutionary affinity. C. Hubbelli differs from C. hastalis, in having slight serrations (small raised bumps) along the blade of the tooth, and superficially appears to be intermediate in shape and function between this “broad toothed” mako form and the modern Great White. The "modern" form of the Great White (indicative of teeth ONLY) is found broadly across the globe at approximately 4 million years ago.  Image via Jeff Gage, of the associated Carcharodon hubbelli fossil. 

6) Great Whites

How does a smaller shark outcompete a signifcantly larger shark? According to the authors of the newly published 2019 study (Boessenecker et al. 2019), it's entirely possible that mature Great Whites were competing for a similar resource with juvenile Megs. According to the competitive exclusion principle, it stipulates that two species can't coexist if they occupy exactly the same niche. 

The huge evolutionary success of the Great White may have resulted in the downfall of the Megalodon. 

So there you have it...  

The Megalodon disappeared anywhere between 3.6-3.2 million years ago, unable to cope with an ever-changing climate and biotic landscape. It's possible that whale migration routes (entering areas of extreme cold, an area in which this macro-predatory shark could not follow), a change in faunal assemblages due to geographical barriers creating a cosmopolitan trend towards hyper gigantism in whales, possible competition from the worlds largest dolphin (the insanely smart Killer Whale) and even rivalry from adult Great White sharks, (which outcompeted juvenile growth stages and presumably occupying the same ecological niche) resulted in the end of this grand lineage of fish. Never again would the oceans hold a macro-predator of such gigantic size... 

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

Pimiento C, Balk MA. 2015. Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators. Paleobiology41(3):479-490

Pimiento C, Griffin JN, Clements CF, Silvestro D, Varela S, Uhen MD, JaramilloC. 2017. The Pliocene marine megafauna extinction and its impact on functional diversity. Nature Ecology & Evolution 1(8):1100-1106

Gottfried MD, Fordyce RE. 2001. An associated specimen of Carcharodon angustidens (Chondrichthyes, Lamnidae) from the Late Oligocene of New Zealand, with comments on Carcharodon interrelationships. Journal of Vertebrate Paleontology21(4):730-739

Ehret DJ, MacFadden BJ, Jones DS, DeVries TJ, Foster DA, Salas-Gismondi R.2012. Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the upper Neogene Pisco Formation of Peru. Palaeontology55(6):1139-1153

Collareta A, Lambert O, Landini W, Di Celma C, Malinverno E, Varas-Malca RM,Urbina M, Bianucci G. 2017. Did the giant extinct shark Carcharocles megalodon target small prey? Bite marks on marine mammal remains from the late Miocene of Peru. Palaeogeography, Palaeoclimatology, Palaeoecology 469:84-91