A shark nerd’s guide to Megalodon: What do we know about this extinct giant shark?

Guest Author: Jack Cooper, MSc
UoB Palaeobiology Graduate / PhD student, University of Swansea

When palaeontologists discuss extinct sharks to the general public, the Megalodon (Otodus megalodon) is pretty much always the first to come to mind. And there’s a good reason why – it’s a giant shark. The name ‘megalodon’ translates to Big Tooth; a name that’s pretty self-explanatory.

Swimming the seas in the not too distant past, Megalodon’s huge teeth have become some of the most iconic fossils in palaeontology. As if those teeth weren’t enough, scientists have even found a few vertebrae. Rarer still is the occasional vertebral column, the biggest of which I’ve been lucky enough to study for myself in Belgium (Fig. 1) [1]. The sheer size of this animal has not only captivated scientists, but inspired several depictions in fiction – be it the “Meg” book series by Steve Alten and the subsequent 2018 film adaptation “The Meg”, two terrible low budget movies called “Megalodon”, or even a few so-bad-it’s-good movies such as “Shark Attack 3: Megalodon” (starring John Barrowman!) or the ever-so-meme-able “Mega Shark vs Giant Octopus.”

However, possibly because of its popularity, there are a lot of public misconceptions about this prehistoric shark. Usually this is the result of its fictional representations. A prime example is that it is often portrayed much larger than it actually was. There have even been fake documentaries claiming its continued existence. But there’s naturally also some scientific debate. It’s understandable that such a widely studied animal has a lot of opinions surrounding it. Every shark biologist I’ve ever come across in my short career, be it those I have worked with or emailed directly, or those I’ve come across on Twitter, has had something to say about this giant.

As such, to paint a clear picture of what scientists have learned about Megalodon, I believe it best to tackle the most basic questions and summarise the research. Such questions are often the most intriguing to the public, and can be rigorously studied by the scientific community. In fiction, we often hear of the 7 basic plots or the 7 basic questions to narrative drama. Taking a spin on this, I present the 7 basic questions of Megalodon, those most often asked by the public, which will be tackled individually in a short series of blog posts:

1. What did Megalodon look like?
2. How big did Megalodon get?
3. When and where did Megalodon live?
4. What did Megalodon eat?
5. How did Megalodon become a giant?
6. When and how did Megalodon go extinct?
7. Is there a chance Megalodon could still be alive today?

Question 1 – What Did Megalodon Look Like?

Getting the obvious point out of the way first, I think we can safely assume that Megalodon looked like a big shark. But what kind of shark? There are over 500 known species today, and their diversity is enormous – ranging in size, diet, habitat and even reproductive strategy [2]. Palaeontologists have therefore tried to identify Megalodon’s closest living relatives to get an idea.

The initial clue comes from the shape of the tooth (Fig. 2). Upon first glance, it bears a striking resemblance to the tooth of the modern great white shark (Carcharodon carcharias). Large, triangular and serrated; these are all key dental traits of a macropredatory shark that snacked on marine mammals. This led scientists to initially brand Megalodon as an ancestor of the white shark. With this came the name Carcharodon megalodon. A skeletal reconstruction led by Mike Gottfried in 1996 subsequently gave it the look of a stockier great white [1]. It made sense at the time; the teeth are so similar in shape that one can reasonably assume that the ecology of Megalodon was comparable to that of the great white.

However, distinct differences between the teeth, and a closer look at the fossil record, suggest something a bit more complicated. The paper that arguably dismissed this initial hypothesis was a particularly clever study from 2006 [4]. Led by Kevin Nyberg, the authors conducted a series of morphometric analyses between the teeth of both Megalodon and great whites among other sharks. They found that Megalodon teeth had no overlap in shape variance with great whites, nor in the shape of their roots. Their scanning electron microscopy (SEM) results revealed that the serrations of white shark teeth were irregular and triangular; whereas those of Megalodon were finer and rounder. Furthermore, Megalodon teeth have thicker lingual sides and a dental band not present in white shark teeth. This collection of evidence suggested that the great white did not evolve from Megalodon as originally thought and instead from a lineage that included mako sharks (Isurus spp.). This old lineage contains similar traits to both great whites and makos, suggesting an evolutionary transition between the two.

This has been enhanced by the finding of some truly remarkable early Carcharodon fossils, which appear to retain tall, narrow teeth seen in makos. These include an exceptionally well preserved fossil containing Carcharodon teeth, vertebrae and even fragmentary jaws (Fig. 3) [6]. This unique specimen came from the Pisco formation in Peru and was recovered in 1988 by renowned shark fossil collector Gordon Hubbell. It was subsequently described by Dana Ehret during his PhD [6], who would then consider the fossil as belonging to an entirely new species. He and colleagues would name this species Carcharodon hubbelli, directly after Hubbell [7].

By sharing mako-like teeth in these jaws, the fossil strongly agreed with the 2006 study’s conclusions that the great white was not a direct descendent of Megalodon after all [6,7]. Ehret and colleagues used this new evidence to officially allocate Megalodon to the genus Carcharocles within the extinct family Otodontidae (aka the megatoothed clade) [6,7]. At this point in the story, Megalodon is now no longer a part of the great white’s immediate family (Lamnidae). However, it remains within the same order (Lamniformes), suggesting that it was more a distant cousin than a direct relative. This of course got people excited as this may well challenge the public consensus that Megalodon resembled a giant white shark.

But wait, there’s more! In 2016, a team led by Kenshu Shimada (who we shall be talking more about in Q2) uncovered fossils belonging to the genus Megalolamna [8]. Its presence within the family Otodontidae found the genus Otodus to be paraphyletic. To resolve this, Shimada and his co-authors recommended that the genus Carcharocles be included in Otodus so that all descendants were accounted for. This brings us to Otodus megalodon, the scientific name Megalodon now generally goes by (although it should be noted that some do still prefer to use Carcharocles). There are even more pieces to this puzzle, including various subgenera the shark could reside in, but we would be here forever if I discussed those.

So ultimately, do all these taxonomic updates actually influence how scientists theorise Megalodon’s appearance? Well, yes and no. With only teeth and vertebrae, it’s extremely difficult to know for sure what Megalodon looked like, but we can make a pretty well-informed attempt. Despite the differences, its dental similarities to great whites do still suggest somewhat parallel diets. Their jaws may therefore have been similar for eating the same kinds of food. Mike Gottfried’s work has suggested that Megalodon needed a robust head with large muscles to support these huge jaws, perhaps resulting in a more curved snout [1]. To sustain its enormous size, it would’ve likely had to eat a lot of food, and/or food of exceptionally high calories. Based on this, most researchers would suggest it had a rather robust body, especially compared to modern macropredatory sharks eating much smaller marine mammals.

I myself have even had a crack at this question. For my MSc thesis at Bristol, I used a combination of geometric morphometrics and linear regressions between total body length and individual body parts in modern macropredatory lamniform sharks to estimate how big these specific dimensions may have been in Megalodon [9]. This work provided the first quantitative estimates of 24 anatomical measurements in Megalodon. I’m going to hold off on revealing exact measurements as this work isn’t published (yet…) but I can say this with confidence: Megalodon’s dorsal fin was tall and narrow, surprisingly similar to that of a great white’s, and could’ve been as tall as an average person at the largest body sizes; its pectoral fins were proportionately longer than those of white sharks; and its tail was enormously tall and probably had a very similar build to most extant lamniforms. My work here was supervised and co-authored by Catalina Pimiento, Humberto Ferrón (both of whom will be heavily discussed in future blogs), and Bristol’s own Mike Benton [9]. Not only can these results tell us how big Megalodon’s body parts were, but allows us to infer its appearance even more.

One thing I’m certain of is that the shark was countershaded in colour, with a darker dorsal side and a lighter underbelly for camouflaging into its background and sneaking up on unsuspecting prey [9]. This is an adaptation seen in almost all living macropredatory sharks, so it makes logical sense that such a recent shark probably had the same trick. Lastly, more current research has indicated that Megalodon may have shared a physiological adaptation with lamnid sharks such as the great white (to be discussed in detail in Q5). Their swimming ecology may therefore have been the same, with similar looking tails and fins supporting thunniform (tail-based) locomotion [9]. As such, Megalodon likely had quite a robust body, with large fins close in shape to white sharks and other ecologically similar large sharks for living a similar lifestyle.

Sorry to disappoint you folks, but the idea of Megalodon sharing many of the same basic characteristics as the great white is still the most plausible theory with regards to its appearance, even though their evolutionary histories were different (Fig. 4). Other theories of its appearance do exist. For example, some think it might have had similar appearances to basking sharks or sand tiger sharks. Given the complete lack of dental similarity (it’s very easy to tell from teeth what a shark was eating) and the fact that the body structure of sand tigers in particular wouldn’t be very viable for a giant, I personally find those theories to be nonsense. To my knowledge, no scientists studying Megalodon have ever seriously considered them. They’re mostly limited to internet comment sections and Deviantart interpretations. It’s fun to speculate for sure, but I like my interpretations to be based primarily around the science. And there has been some truly wonderful science around this animal, which has allowed us to discover so much about how they lived…

References

1. Gottfried MD, Compagno LJV & Bowman SC 1996. Size and skeletal anatomy of the giant “megatooth” shark Carcharodon megalodon. In: Great White Sharks: the biology of Carcharodon carcharias (eds. Klimley AP & Ainley DG), 55–66, Academic Press, San Diego.
2. Compagno LJV 2001. FAO Species catalogue. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. FAO Species Catalogue Fishery Purposes 2.
3. Reolid M & Molina JM 2015. Record of Carcharocles megalodon in the Eastern Guadalquivir Basin (Upper Miocene, South Spain). Estud. Geol. 71, e032.
4. Nyberg KG, Ciampaglio CN & Wray GA 2006. Tracing the ancestry of the great white shark, Carcharodon carcharias, using morphometric analyses of fossil teeth. J. Vertebr. Paleontol. 26, 806-814.
5. Ward DJ & Bonavia C 2001. Additions to, and a review of, the Miocene shark and ray fauna of Malta. Central Mediterranean Naturalist 3, 131–146.
6. Ehret DJ, Hubbell G & MacFadden BJ 2009. Exceptional preservation of the white shark Carcharodon (Lamniformes, Lamnidae) from the early Pliocene of Peru. J. Vertebr. Paleontol. 29, 1-13.

Edited by Rhys Charles