Megalodon: Inside the Life of a Superpredator
SHOW NOTES
Although we will mainly be discussing Megalodon today, Jack’s research goes way beyond the legendary giant [8.00]. He studies the functional diversity of sharks through time, which essentially means understanding the ecological roles played by sharks across the last 66 million years. Like modern sharks, prehistoric sharks would have occupied a variety of positions in the marine food web. Some, like Megalodon, would have been apex predators right at the top of the food chain – but others would have been mesopredators, serving as both predator and prey. They would have also had vital ecological functions, transporting nutrients within or between habitats and helping to maintain balanced, healthy ecosystems. Jack is interested in identifying the ‘functional traits’ of these ancient species, which are things like body size and diet, that could indicate what role they played in the ecosystem. In doing so, he can also try to understand what the consequences were when these species went extinct. This information can help us in present day, informing how their current extinction crisis might affect our delicately balanced ecosystem.
Gaining this information is no small feat, given that most of the time all we have left of these species are a handful of teeth [9.48]! Sharks have skeletons made entirely of cartilage, which tends not to fossilise as well as bone. There are some instances where thicker and more calcified parts of the skeleton have fossilised – for example, some megalodon vertebrae have been discovered, which we will come to later on – but these are extremely rare. For the most part, the shark’s teeth are the only thing that have preserved in the fossil record. This means that paleobiologists like Jack, who specialise in sharks, have to do some serious detective work! As Jack says, “you’re piecing together all these tiny clues to work our what it looked like, or what it was doing. And that’s a common grey area with shark fossils. We can reasonably assume what they may look like, but the truth is we can’t know with certainty until we get a complete skeleton.” For example, we are able to reliably assume what a dinosaur like Tyrannosaurus rex looked like, as there are quite a few complete skeletons. But sharks are a whole different ballgame…
There are some things about megalodon that we are fairly certain about, however [14.26]. As far as we know, megalodon was the largest shark to have ever existed. Using the size of their teeth, scientists estimate that megalodon could have reached a maximum length of twenty metres – but more conservative estimates place it at around fifteen metres long. It was a predator, feeding on large whales. We know this from whale bone fossils that have megalodon teeth embedded in them! And, we know that megalodon roamed the seas from the Miocene to the Pliocene epochs, roughly 23 – 3.6 million years ago.
The ocean then was very different to today [16.00]. In general, sea temperature was much warmer, especially in the Miocene. We’re talking higher temperatures than what is considered ‘tropical’ by today’s standards, as sea temperatures have broadly declined ever since. The waters were also more productive, supporting a greater diversity of marine life. This means that there was plenty for megalodon to be feeding on – something that was key to their survival.
A common misconception about megalodon is that they essentially looked like a giant version of the great white shark [18.02]. Previously, scientists believed that white sharks were direct descendants of megalodon, but thanks to further discoveries the shark family tree has now changed. It turns out there are very slight differences in their teeth. The teeth of megalodon are thicker, and have a dental band not present in that of a white shark’s. Both are serrated, like a steak knife – typical for an apex carnivore, suited for tearing and cutting meat – but under a microscope the serrations are subtly different between the species. It may not sound like much, but it was enough evidence to suggest that, while megalodon would have had similar ecological traits to a white shark, they are in fact from different lineages. It is now widely understood that megalodon was the last of the ‘megatooth’ sharks, a group of giant mackerel sharks that steadily got larger and larger. Further, the last common ancestor shared between them and white sharks was back in the Cretaceous period – some 145 to 66 million years ago. From there, the ancestors of megalodon and white sharks went their separate ways and had completely different evolutionary trajectories.
The megatooths themselves were very interesting [20.01]. They are known as a ‘chronospecies’, where there are only subtle changes through time. The earliest known species is Otodus obliquus, which was already around eight metres long – still bigger than the largest macro-predatory shark alive today, but not quite as big as the filter feeders. Over time, the megatooths evolved to become larger, with bigger and more serrated teeth. This might be due to their diet. Around the same time, marine mammals began to evolve, also becoming bigger and faster. There is still debate around this, but there are some fossils that show evidence of Otodus’ feeding habits. Some fossilied whale bones have bite marks that have been matched to megalodon teeth, or they have been found in the same location as the teeth themselves. There are also some pretty gruesome fossils that suggest a whale’s vertebrae was almost snapped in two by a potential megalodon bite! Scientists have even been able to look at how the bone healed and regrew to estimate how long the whale might have lasted with such a nasty injury – potentially about six weeks. “I suspect this poor whale was in agony for those last six weeks.” Says Jack. But the severity of the whale’s injury demonstrates how powerful a bite megalodon would have had. “There have been a couple of previous studies that have tried to calculate [megalodon’s bite force] – most of them will extrapolate from the great white Shark because their teeth, despite those distinct differences, are broadly similar in that they’re both big, triangular and serrated.” Jack explains. “And the original paper calculated the great white sharks bite force and found it to be one of the highest of the animal kingdom today. Megalodon’s was at least an order of magnitude larger: the maximum bite force they got was 180 ,000 Newtons. Which if that’s accurate, that is the strongest bite force we know of of any living animal, living or extinct, in history.”
So, we know that megalodon was a huge shark, with a bite force to match. But what did they actually look like [25.30]? Jack has been leading on research that modelled the size and proportions of megalodon, using just their teeth, some exceptionally well-preserved vertebrae, and some examples of modern-day sharks with similar lifestyles. Megalodon is in the order Lamniformes, or the mackerel sharks (the same as white sharks). This means that there were 15 potential ‘analogues’ from the extant lamniforms that Jack could choose from – comparable species from present day. Of these fifteen extant species, Jack chose those that had potentially similar diets and physiological traits to megalodon. Specifically, Jack was looking at regional endothermy (which we covered in detail on a recent episode with Haley Dolton!). Essentially, regional endothermy is a trait exclusive to the lamniforms that allows them to heat certain parts of their body, and retain that heat. It is though that megalodon was regionally endothermic – which makes sense, given it’s lifestyle as an apex superpredator. Regional endothermy would have allowed megalodon to swim faster and cover longer distances, much like today’s apex sharks. So, Jack selected five current species that had been shown to have similar lifestyles and physiological traits to megalodon: the porbeagle shark, short and long-fin mako sharks, salmon sharks and, of course, the great white shark. Using measurements of the body proportions of these sharks compared against their total length, and with fossilised megalodon teeth, Jack and his team were able to ‘reconstruct’ megalodon. The result? Essentially a bulky, stocky lamnid, or in jack’s words, “an absolute unit of a shark”!
Jack and his team made three ‘versions’ of megalodon [33.35]: a ‘baby’ megalodon, which still would have been an astonishing three metres long, a juvenile megalodon at eight metres, and an adult at sixteen metres long. For the latter, the size of the fins alone is mind-blowing. According to the model, a sixteen metre adult would have had a dorsal fin the same size as an average human! They also had long, elongated pectoral fins, to provide that huge body with enough lift to propel itself through the water. “It perhaps looked more like a salmon shark or porbeagle, with a stockier, shorter snout….or perhaps it looked more mako-like. But generally we think it looks essentially like a stocky lamnid.” In a very basic sense, a very big version of your ‘typical’ sharky shark!
Do you remember the exceptionally rare fossilised megalodon vertebrae we talked about earlier? Well, when it came to creating the most complete 3-D reconstruction of megalodon to date, these came in very handy [37.30]. Back in the 1860s, an entire vertebral column of megalodon was found. There were over 140 vertebrae in total, and from the texture, size and colouring, it could be deduced they were all from the same individual shark. The specimens essentially sat in a museum for 70 years, until a team led by Michael Godfrey arrived to reconstruct the largest shark that ever lived. Later, Jack’s future PhD supervisor and director of the Pimiento Research Group Dr Catalina Pimiento, along with Professor John Hutchinson – an expert in 3D modelling of extinct taxa – managed to 3D scan the entire vertebral column. But there were still some gaps that needed filling…the rest of the shark’s body, to be exact. And this is where Jack came in! Using a 3D body scan of a great white shark and some impressive modelling skills, they were able to fully reconstruct the megalodon’s body, which gave them critical insights into not only it’s size and body mass, but also the type of life it might have lived.
For starters, Jack’s work estimated that a 15.9 metre shark would have weighed an astonishing 60 tons [40.23]! They also were able to figure out that megalodon could cruise around the ocean at speeds of about 1.4 metres per second – similar to a typical great white shark – which fit with the theory that megalodon was an active, agile predator. And what is essential for that kind of lifestyle? A lot of calories! “We found a stomach capacity from about 10 ,000 litres, which was big enough to fit an entire killer whale.” Says Jack. “So that gave us, that gave us a nice sort of edge to think, okay, this thing’s trophic level is probably higher. They can eat a killer whale, which is of course famously the top predator in today’s oceans…and, a megalodon of our model size would have needed up to 98,000 kilocalories every day.” Does that mean that megalodon would have needed to be constantly hunting to sustain itself? Well, not exactly. “Interestingly, megalodon could have sustained itself by eating either a lot of small whales, or by eating one very big whale and then undertaking a transoceanic migration for two months.” Explains Jack. “And what we find exciting about that is that we know great white sharks undertake migrations that long. There’s the famous great white shark, Nicole, that went from Gansbaai in South Africa all the way to Australia and back again. So we like to think Megalodon was doing this too. And incredibly excitingly, just last year, a paper was published that found essentially an in situ megalodon tooth in the middle of the Pacific Ocean. They did not find any evidence that had been moved a lot by geological activity. And in my mind, the only biological explanation for this is that a megalodon was taking a meal during a migration across the Pacific Ocean. It killed something and lost the tooth in that time. So it’s been very nice to see fossil evidence supporting that coming out.”
Something else that Jack has tried to determine with this research is the impact of Megalodon’s extinction on the marine food web [50.12]. The loss of an apex superpredator, especially one that was found in almost every ocean at that time, was bound to have a profound effect. Essentially, we lost a chunk of functional diversity in sharks because of megalodon’s extinction, as megalodon occupied a higher trophic level than any shark alive today. The role of ‘transoceanic superpredator’ seems to be one that died with the meg, which had a number of consequences – particularly for cetaceans. Something that Catalina Pimiento discovered in her PhD was that shortly after megalodon went extinct, whales were free from the pressure of their giant predator and began to get larger and larger. “If I’m not mistaken, the blue whale evolved after megalodon went extinct, which is of course the biggest animal that’s ever evolved!”. So, in short, one giant gave way to another.
So what happened to cause megalodon’s extinction [54.50]? The exact reason is still widely debated, but it is most likely down to a number of factors. Firstly, a marine megafauna extinction event occurred during the Pliocene, which would have taken away some of megalodon’s crucial calories. Sea temperatures were also dropping, as was sea level – shrinking available habitat. And, critically, other predatory sharks began to evolve, notably the white shark ancestors. Ordinarily they wouldn’t have been much competition for megalodon, but in combination with less available prey and habitat, it could have been the nail in the coffin.
Does this mean that there’s little chance megalodon could still be hiding in the deep, waiting for an unsuspecting Jason Statham to discover it? “I can see where the hope comes from in that it only went extinct recently. People want to be excited by the mysteries of the ocean, what’s out there.” Jack answers. “Of course, you could argue why just Megalodon? Why not all the other extinct sharks that could be there…but no, and we can say with utter certainty that megalodon is definitely extinct. We have no fossils of its teeth or vertebrae or anything dated beyond 2 .6 million years ago. We also love the beach, and we’ve never seen one out there in the beach. There is a quite a niche paper by a researcher named Tyler Greenfield from a year or two ago that actually tried to investigate historical claims of a living megalodon and found there was nothing credible in them at all. So it’s nice we have a scientific paper actually trying to get into this. But even without it, we can say with very, very strong confidence and complete certainty, the only way you’re going to see a living Megalodon is in a Jason Statham movie.”
Maybe a slight disappointment for any megalodon fans out there – but perhaps if they were still around, we wouldn’t have the blue whale!
ABOUT OUR GUEST
DR JACK COOPER
Jack is a paleobiologist based at Swansea university. His research concerns the functional diversity of sharks through time (~66 Ma-present). This involves examining ecological changes of sharks across the last 66 million years using fossil teeth. Jack has received sponsorship from the Fisheries Society of the British Isles and is a member of the Pimiento Research Group, which aims to assess extinction mechanisms of marine megafauna such as sharks through time. The ultimate goal of the team is to use this information to inform ongoing conservation efforts. Jack is involved in research on the giant megalodon shark.
Additionally, Jack engages in outreach of shark palaeobiology through a variety of ways. His outreach, as well as previous work he has published, primarily focuses on the iconic megalodon shark, its biology and ecology, and what the extinction of this apex predator could tell us about the effects of future shark losses.
You can follow jack on X/Twitter (@cooperpaleo) and check out his most recent publications here.
You can also follow the Pimiento Research Group here.
