Imagine the seas off Peru, 6 million years ago. A group of long-nosed dolphins swam through the warm seawater, breaking the surface with occasional enthusiastic leaps into the stark sunshine, then diving crisply back into the clear water to join their compadres.
Not far away, a pod of small baleen whales headed southward to feed in the nutrient-rich Antarctic waters. Three males and four females were clustered together in a rather tight formation as they swam along at their regular pace, always wary of imminent danger.
About 6 million years ago, the seas off Peru were much warmer than today, by at least 4°C. The middle part of the Miocene period (23–5.3 million years ago) had been a warm time throughout the world, with sea temperatures soaring to 31°C in places. That was a time of great expansion of whales and other marine life as productivity soared in the oceans.
In the final million years of the period, two of the three marine gateways connecting the warmer tropical seas together had closed, blocked by tectonic uplifts. This caused a dramatic rerouting of oceanic currents, resulting in abrupt cooling of the oceans. Food resources were on the wane, so predators had to hunt harder for food.
Gigantic predators had an even harder time, as they needed much more food each day than smaller creatures.
‘A blood-curdling horror’
The little whales belong to an extinct species called Piscobalaena. They were slow-moving animals that looked a lot like a scaled-down version of today’s southern right whales, with the oldest individuals reaching around 5 metres.
The dolphins belonged to an archaic type named Atocetus, ancestors of the living La Plata dolphins that would later inhabit the same bountiful seas. They watched the pod of small whales out of the corner of their vision, as both groups moved on warily, their keen sense of echolocation sounding out the waters around them for both food and signs of danger. Suddenly the returning sound waves signalled danger.
A large living mass was moving in the waters ahead, coming at a fast pace straight toward them. It was a menacing thing to detect when nothing at all was visible in the water ahead. The nervous dolphins began to speed up, moving quickly below the surface as the whales huddled closer together, changing course to head at right angles as quickly as they could away from the path of the large incoming creature.
What the dolphins saw next was a blood-curdling horror straight out of a nightmare.
The massive 16-metre shark crashed through the gloomy waters to charge upward and breach the water, seizing one of the baleen whales in its powerful jaws. Otodus megalodon had made its entrance.
This mature female shark could have weighed nearly 60 tonnes, so the much smaller whale had no way to escape her jaws – nearly 2 metres wide and lined with unforgiving rows of thick, serrated triangular teeth.
When coupled with the incoming momentum of the shark’s massive body weight, the jaws rammed the prey and, as the beast crashed down into the water, with one powerful bite sliced the defenceless whale into two neat halves. Thick red billows of blood darkened the water.
With a sharp turn of its head, the gargantuan shark swooped to finish the job, gulping the tail and body of the whale, taking the last chunk of bleeding flesh in one large swallow.
Other large sharks, like the archaic white shark, Carcharodon hastalis, around 7 metres long, were now sensing the metallic tint of blood in the water, tentatively homing in from far and near to join in the feeding frenzy.
The Otodus megalodon swung around and began chasing one of the smaller female whales. The pod, confused and highly distressed, tried to dive deeper to escape the lurking danger.
With a powerful thrash of its huge, forked tail fin, the killer shark sped swiftly down, snatching a second whale, biting a third of the animal off, before swallowing the chunk whole. It turned around and savaged the bleeding carcass, shaking it in its enormous head, scaring away the smaller sharks that had come in to share in the bloodfest.
Within a few minutes, she had swallowed the second whale, not quite enough to slake her monstrous appetite, and headed back to clean up what was left of the first victim.
Smaller sharks had arrived on the scene en masse. They began tearing the bloody remains of the first whale into shreds, when Otodus megalodon once more came thrusting in, shaking its gruesome head to scatter the smaller predators as a horse deflects flies. She chomped at what was left of the whale’s shredded body, swallowing the last bloody pieces in one gulp.
The smaller sharks, some up to 7 metres long, included enormous extinct species related to the mako and one of the first of the modern white sharks. They were mere minnows in the shadow of this beast. The monster was now satiated, bloated by the massive meal of two small whales. Slowly she moved away from the scene, leaving the other whales to flee hastily on their southward journey.
Otodus megalodon, the queen of the killer sharks, was the most powerful superpredator Earth has ever seen either on land or in water.
Superpredators are creatures capable of killing prey equal to or larger than themselves, and this shark clearly had that ability. Because there is a genus of clam called Megalodon (the name simply means “large tooth”), we will use “megalodon” (lower-cased and unitalicised) as our common name for this giant shark.
You might think that we palaeontologists make up scenes like this, but nature is more imaginative than anything our human brains can conjure. While it’s true that I choreographed this frightening scene in my head, nature provided the dancers and told us what moves they could perform.
Megalodon: how big was it?
Megalodon was not just any predator, she was the predator, the most ferocious creature who ever lived, with the deadliest jaws of all time, spawned from the dark side of nature.
The jaws of a maximum-sized female (females were larger than males) could deliver the strongest bite force of any creature that has ever lived, a whopping 2.8 tonnes per square centimetre in each fatal chomp of its jaws. That is enough strength to crush a pickup truck and have some force still left in the megalodon’s tank. She was three times more powerful than Tyrannosaurus rex, the largest land predator of all time.
Megalodon appeared around 23 million years ago and disappeared around 3.6 million years ago. O. angustidens, its immediate ancestor, was slightly smaller but morphed into this new, larger form when ocean temperatures cooled slightly, providing an increase in oceanic nutrients, which fuelled larger populations of its favourite prey, large filter-feeding whales.
Here at last we have reached the pinnacle of 460 million years of shark evolution, the largest shark ever and Earth’s biggest predator.
People of all generations, young and old, have feared it since the first reconstructed gigantic toothy jaws of it began to grace our museums nearly a century ago. Even today it remains a powerful research magnet for some paleontologists, who can’t pull themselves away from the lure of its enticing fossil remains.
We continue to study its fossils through new technological approaches to discover unexpected new things about how it lived, what it ate, and clues to why it went extinct. It also has a strong grip on the minds of “cyptozoologists” – people who still believe it might be alive out there in our ocean.
The most commonly asked question about megalodon is: how big was it?
If we simply use the relationship that exists between tooth size and body size in the great white shark (as a model) and extrapolate the same relationship to megalodon, we could derive an approximate maximum size for this monster fish at between 16 to 21 metres. Its mass would have been 25 times the mass of the largest white shark, maybe reaching 55 tonnes, much heavier than the biggest Tyrannosaurus (9 tonnes) or any other land-based predator you choose.
In recent years, a new way of estimating the size of sharks uses the maximum jaw width as shown by the teeth. Using this new method gives new maximum size for megalodon of around 21 metres long.
Another paper published straight after this one, led by Jack Cooper from Swansea University, calculated the size of different body parts for megalodon individuals of different lengths. It concluded that a megalodon reaching 16 metres would have a head about 1.5 metres in length and a tail fin that was 3.8 metres in height. The large triangular dorsal fin would have been about the same height as an average adult person.
You can see a full-sized megalodon model hanging in the foyer of the Smithsonian Museum of Natural History in Washington, D.C. It was built in 2021 under careful scientific direction and spans just over 15 metres. It is impressive to see its massive body and huge jaws bristling with triangular serrated teeth. Other stunning models of megalodon, or its reconstructed jaws, are displayed in several other museums around the world.
For the past century, every classic reconstruction of megalodon, including many recent ones in the movies, show it as a scaled-up white shark, since it was commonly thought to be an ancestor of the living species. The most recent data about megalodon’s body shape was published in early 2024 by a consortium of 26 renowned fossil shark experts led by Phillip Sternes of the University of Washington.
They showed that its body shape was more elongated than that of the white shark, and the tail would have had a longer upper lobe. Its body might have looked more like that of a basking shark, with a longer tail for slower ocean cruising. This study was based on spotting an error in a previous interpretation of the vertebral skeleton of the articulated megalodon from Belgium.
It demonstrated that all previous reconstructions of megalodon that used the white shark as model for its body shape are incorrect. This has serious implications for future Hollywood productions, as every B movie ever made about this shark used scaled-up white sharks to make their CGI megalodons (back to the drawing board, guys!).
This iconic extinct shark is known principally from its huge fossil teeth, and sometimes rare articulated remains of large, calcified vertebral discs, like the superb fossil from Belgium now in the Royal Belgian Institute of Natural Sciences, which comprises 141 associated but slightly disarticulated vertebral discs and no teeth. It measures around 11 metres long, yet is incomplete, and from the growth rings in the discs we find it was 46 years old at death. It must belong to megalodon, as no other shark of this age grows to such large size.
Recent study of megalodon’s scale shapes, based on a partial skeleton found in Japan, revealed that it was generally a slow-cruising shark capable of an occasional burst of speed to catch its prey. Kenshu Shimada estimated from the scales that it swam through the ocean at around 2.8 kilometres per hour, which is slower than most of the living lamnid sharks, including the white shark, which cruises at between 3–3.5 kph.
Queen of the Megalodons
Catalina Pimiento, whom I call Queen of the Megalodons (she approves), is the world’s leading expert on this species. Her work helps us understand why researching the long-dead remains of a gigantic shark is useful today, leading us to better understand the factors that are now changing our world.
Her research has shed new light not only on the biology and lifestyle of this giant shark, but also on how it coped with major shifts in global climate and oceanic circulation in the Miocene and Pliocene periods (between 23 and 2.6 million years ago). And she has made the most detailed study of the factors that drove it to extinction.
Catalina grew up in in Bogotá, Colombia, keeping her head low and going to school during a time of violent civil unrest that resulted in hundreds of thousands of victims. Her undergraduate work was on living whale sharks, and this became her hook into marine biology, leading her eventually to the University of Florida.
While she intended to work on living sharks, her supervisor suggested she might look at a project on fossil sharks. Catalina agreed and began working on a site in Panama where middle to late Miocene shark teeth were found, so she collected and described this new collection of fossil sharks.
She is the only person I know who has written two postgraduate dissertations on megalodon. These works dragged her willingly into the world of fossil sharks, gravitating around the big body mass of megalodon and the mystery of its extinction.
Her first question to solve was what the average size for a megalodon was and whether this size changed over geological time. Catalina looked at thousands of fossil megalodon teeth from around the globe to discover new insights into the daily life and ultimate demise of megalodon. She proved megalodon had an average body size around 10-11 metres for the 14-million-year period the samples represented.
The megalodon was huge, so how did it fill its belly in its endless search for food and energy?
Megalodon: the ultimate predator
We know of two nearly complete sets of megalodon jaws – one from Saitama, Japan, and one from the Yorktown Formation in Maryland.
The latter was used as the basis for a complete reconstruction made by the Smithsonian Natural History Museum in 2020. That reconstructed life-sized set of megalodon jaws is nearly 3 metres high by 3.4 metres wide and contains nearly full rows of fossil teeth in every jaw position (182 teeth in all, although a complete megalodon jaw is estimated to have had around 276 teeth).
We have many thousands of good examples of megalodon teeth from many sites around the world, including some that made their way to the surface as part of the dredging of the deep ocean seabeds.
We bone detectives can deduce a lot about megalodon’s lifestyle from studying the teeth and deciphering the geological context of where they were deposited. For example, they tell us where it lived and at what time, and what it ate, from toothmarks it left on bones or from the teeth it left embedded in them.
The biggest megalodon teeth are fat triangular teeth measuring just over 7 inches long, adorned with sharply serrated biting edges like a jagged steak knife. They have been found in every part of the world except Antarctica (where we do have Pliocene fossil deposits with fossil whales but no megalodon teeth). This tells us that even with its huge body mass there were still parts of the world where it would not venture because of the extremely cold seas.
So, with such powerful and terrifying jaws, what did megalodons like to eat?
In our scene at the start, I imagined the shark hunting the small Piscobalaena whales, because we have direct evidence of megalodon tooth marks incised into the bones of this fossil whale. Other bones of seals show megalodon tooth cuts as well. Their big teeth leave distinctive cut marks that look like deep trenches of dotted lines caused by the tooth’s serrated edges slipping over the bone surface.
The fossil whale was attacked from the side, targeting the head region, as the cuts are found on the lower jaws, while the seal was bitten around the shoulder, suggesting the top half of the body might well have been severed by the powerful bite.
Megalodon tooth scars have been found on the tooth of a large extinct sperm whale that lived 5 million years ago. The deadliest and most spectacular of all the predatory whales at this time was one whose name harks back to biblical and literary fables, Livyatan melvillei (honouring Herman Melville and Moby-Dick). It had deadly curved tusks lining both its jaws (modern sperm whales have only lower jaw teeth).
It reached a maximum body length of around 17 metres. I have no doubt that both these giants preyed on each other at different stages of their lives — adult megalodons feeding on juvenile Livyatans and vice versa. We can also determine what megalodon was eating from the chemistry of its fossil bones and teeth.
Zinc is a necessary element for the mineralisation of skeletons, especially teeth. It is acquired by eating certain types of prey, and certain isotopes of zinc can be traced in the shark’s teeth. By analysing the ratio of zinc isotopes, scientists can plot what level of the food chain ancient sharks were occupying.
Using this method, a team led by Jeremy McCormack of the Max Planck Institute in Germany was able to determine that megatoothed sharks were eating high-level food resources like marine mammals. The ratio of certain isotopes of zinc in the tooth enameloid of fossil sharks determined whether the shark was a top predator, based on comparing the same zinc ratios in various living sharks.
What Jeremy and his team also found was that during the Pliocene period (5.3 to 2.6 million years ago), the emerging guild of white sharks occupied the same niche as megalodons — in other words, eating much the same prey.
While this finding might suggest that the increase in abundance of white sharks at this time could possibly explain the demise of megalodon from stiff competition for the same food resources, there is no hard evidence that this was really the main cause of megalodon’s extinction.
For example, today we find that orcas coexist with white sharks and still eat similar large prey items — small whales, dolphins and seals — but one is not driving down the population of the other as far as we can see; rather, populations of both are kept in balance by the amount of prey resources available.
Fossils confirm that orcas and white sharks have coexisted happily for at least the past 6 million years, a similar time that white sharks swam alongside megalodon.
The lamniformes sharks include the only shark species that can generate higher body temperatures than surrounding seawater by capturing heat generated from their powerful body muscles. Therefore, they are essentially warm-blooded or endothermic. Today, these are the white shark, makos and thresher sharks.
Paleontologists have speculated that as megalodon is one of the lamniformes with a lifestyle similar to that of the white shark, an apex predator hunting marine mammals, it also would likely have been warm-blooded. Some suggested its body temperature might have been as high as (35°C). This would have made it easier for megalodon to cruise across oceans with fluctuating water temperatures or venture into colder, higher latitude seas rich in nutrients where whales like to feed.
This was all speculation, until a breakthrough was announced in mid-2023 that provided hard evidence megalodon was warm-blooded. The state-of-the-art method of clumped isotope paleothermometry, which measures the temperatures of chemical bond formation in the tissues of the teeth, shows that megalodon really did have a highly elevated body temperature of around 27°C.
The researchers also calculated the temperature of the seawater from oxygen isotope formed in clam shells found with megalodon teeth in the same fossil deposits. This showed the giant shark had a body temperature about 7°C higher than the seas it lived in.
Today’s whale sharks have a similar body temperature to that calculated for megalodon, but they do this through living in warmer seas — they do not generate their own internal body heat. The megalodon’s warm-blooded metabolism could have been a key driver of its growing large so quickly. One study suggested that its body heat was needed for digestion of large pieces of ingested whale meat as well as for absorbing and processing nutrients.
Another, somewhat darker theory has recently emerged that could explain why sharks like megalodon and its ancestors could have grown so big and been warm-blooded. The lamniform sharks, the group that megalodon belongs in, are today characterised by their intrauterine cannibalism. This occurs when the young hatch from eggs inside the mother and begin to eat the unhatched eggs, or even other baby sharks, still inside the mother’s womb.
Because the large lamnids, like white sharks, makos and thresher sharks, are warm-blooded, they have higher energy requirements than most other sharks. The intrauterine cannibalism raises their body temperature slightly higher than the seawater in which they live, enabling them to hunt in colder waters and to swim faster. According to DePaul University shark palaeontologist Kenshu Shimada, this warm-blooded condition in lamnid sharks could have “pushed up the internal heat” levels required for a big megalodon, also speeding up its growth rates.
Why did megalodon go extinct?
We have now seen how abundant and successful megalodon was – so what caused its ultimate demise? How does such a mighty shark at the apex of the ocean’s food chain go extinct? Was it a global climate change trend, or did its prey suddenly die out? What evidence do we have for assessing its extinction? The sudden disappearance of megalodon sometime around 3 million years ago remains one of the great mysteries of shark paleontology.
Let’s start by looking at what was going on with respect to continents moving, currents shifting, and climates changing during the last few million years of megalodon’s reign.
At the start of the Pliocene (5.3 million years ago), global temperatures rose to about 2–4°C higher than they are today. Then things turned around at 3 million years ago, when there was a dive in sea temperatures as the Arctic ice cap formed and cold currents flowed up from the Antarctic. The warm equatorial currents that flowed around the globe ended when the long, slow collision of North and South America finished around 2.7 million years ago, as the Isthmus of Panama rose from the seafloor.
At this time, we find giant land animals moving between South America and North America — ground sloths, elephants, sabre-toothed cats and many other creatures — in what is called the Great American Biotic Interchange. Seaways that might have been migratory pathways for big sharks like megalodon suddenly closed.
Using her database of many hundreds of megalodon teeth finds from around the world, Catalina Pimiento compared the abundance and geographical range of teeth with causal factors like sea level changes and consequent habitat loss. Her conclusion was that the reduction of coastal habitats, as sea levels fell because of growing ice caps at the poles, caused a collapse of the marine ecosystems necessary for sustaining the entire food chain of the oceans.
This environmental change caused the extinction of one-third of the marine megafauna — not only megalodon, but also many species of whales, sharks, large sea turtles and huge flying seabirds — at the end of the Pliocene, around 2.6 million years ago.
The collapse of these ecosystems implies that megalodon lost many of its primary food sources during this time, as many species of whales went extinct, driving it to its demise.
British fossil shark expert David Ward thinks that megalodon could have bumped out a little earlier than this date, as he doesn’t know of any megalodon teeth that have been reliably dated younger than 3.7 million years old. Either way, we can say with utmost confidence that the last megalodon went extinct sometime between 3.7 and 2.6 million years ago.
The exact reasons for megalodon’s demise remain unknown, but they could relate to either ocean cooling with the onset of ice ages, starting about 2.6 million years ago, causing the habitat loss discussed above, or biological factors like the events surrounding the evolution and migration of whales to colder Antarctic waters where the sharks could not go.
It seems likely that the growth and huge size of modern baleen whales, the largest animals on the planet, could well have been driven by predation pressures from megalodons. Their ability to endure and feed in near-freezing Antarctic waters might have been a factor in why megalodon went extinct.
Whales cope well in Arctic or Antarctic waters, but no sharks today can survive in waters that are as low as 0 to -1.7°C. The annual migration of large filter-feeding whales to feed in rich Antarctic waters might have been the last straw in the megalodon ecosystem collapse. It likely went extinct with a whimper rather than a bang.
This is an edited extract from The Secret History of Sharks: The Rise of the Ocean’s Most Fearsome Predators by John Long (Quercus Books, Australia; Ballantine Books, USA).
John Long receives funding from The Australian Research Council
This article was originally published on The Conversation. Read the original article.
