Imagine swimming in the ocean. You’re splashing around, minding your own business,  when all of a sudden a shark fin the size of a boat pops out of the water and heads straight towards you. That would probably be the last time you stepped foot in the ocean,
if you made it out alive that is. The only shark that could have a dorsal fin of that size would belong to a megalodon. Luckily for you—and all of us—the megalodon went extinct around 3.6 million years ago. But what caused this massive apex predator to die off?  And is there a chance that it is still lurking in the depths of the oceans? The megalodon or Carcharocles megalodon first inhabited the oceans of planet Earth around 23 million years ago. They were the largest shark to ever live. Megalodons varied in size,  but studies suggest that on average a female meg could be between 45 and 59 feet long. This range varies so widely because scientists need to extrapolate the size based on teeth and jaw fragments found in the fossil record. At this point in time, a full megalodon skeleton has not been found. However, from the remains we do have, it is clear that these creatures were enormous.
Adult megalodons had no predators because of their massive body size. The shark’s main prey was small whales. That’s right, they ate whales, that’s how big they were. Megalodons roamed every ocean of the world, although they stayed away from the polar regions where the water would be too cold. What we know about the megalodon species comes from fossil remains and scientific observations of their much smaller relatives that live today. The largest predatory shark species alive today is the great white. The largest great white ever recorded was around 36 feet long. This makes it 20 feet shorter than the megalodon. Megs were truly massive sharks. Megalodons were incredibly successful at what they did. They outcompeted other predators for about 20 million years and stayed at the top of the food chain for that entire time. Their size, razor-sharp teeth, and speed allowed them to hunt and kill prey with deadly efficiency.
So, what caused the Megalodon to go extinct? Why isn’t this incredibly successful killing machine ruling over the oceans today? There were probably several factors, but evidence points to a few clear changes that had a big impact on the megalodon survival rate. Between 3 and 5 million years ago the climate began to change on planet Earth. The world began to cool as it entered the epoch known as the Pliocene. As global temperatures dropped the oceans were affected. One major change that occurred as temperatures cooled was that the sea levels began to drop. This happens during ice ages, and periods of cooling because the water of the oceans gets trapped in ice and glaciers.  As the water gets converted into its solid form,  it is removed from the oceans. This causes the overall sea level to drop. The dropping of the global sea level wouldn’t have been a problem for megalodon if that was the only change that occurred, but when the sea level dropped, new land started to form that had previously been underwater. During the Pliocene, the Isthmus of Panama began to take shape. The collision of tectonic plates in the area caused volcanic activity that resulted in the formation of the mountains that now stretch from North to South America. The emergence of this new land that connected the Americas had a huge impact on the animals of the oceans. The land that would become Central America had been underwater for millions of years,  meaning that there was nothing blocking marine species from crossing between what would become the Atlantic and Pacific Oceans near the equator.
Once the access between the Americas was blocked off by land, many species were now stuck either on one side of the continents or the other. This meant that access to some of the megalodon’s prey may have been separated from them. Ocean currents and the movement of nutrients in the oceans began to shift once the equatorial connection between the oceans was impeded. This would have caused species to migrate to new areas, or if they could not adjust to the new environment they would go extinct. The currents and nutrients that once flowed between the Americas would have been abruptly brought to a halt. Without these nutrients, biodiversity would drop. This change would have a domino effect on all species living throughout the oceans. Nutrients would no longer be where they once were, and entire ecosystems would have vanished. This alone would have caused mass extinctions of aquatic organisms, leaving room for new species to evolve. Even if this lowering of ocean levels, and the blockage between the oceans,  did not directly cause megalodon to go extinct, it most likely had an impact on their prey. Since megalodon was large and slow to reproduce, it filled one specific niche,  that of an apex predator. If the environment suddenly changed, it was unlikely that megalodon had the genetic diversity to adapt to a new environment with less prey. Another impact of the lowering of ocean levels is that the oceans become saltier. As more and more water is trapped in ice and glaciers the salt to water ratio in the ocean changes.  The salt does not get trapped with the water, so salt levels remain constant, while water levels decrease. This causes an increase in salinity throughout parts of the oceans. The difference in saltiness would have shifted the ocean currents, and nutrient cycles, evermore. In fact,  this change in salinity is one of the main reasons we have the ocean conveyor belt of today.
All of these changes to the oceans would have meant the environment that the megalodon had been so successful in for millions of years,  was now different. It is very difficult for large specialist predators to adapt to changes in their environment. Think about what is happening in the arctic right now to polar bears. They are highly specialized for the environment they evolved in, but if the ice continues to melt,  and the global temperature continues to rise, they will go extinct. The polar bear species just does not have enough genetic diversity to allow them to be successful in a warmer environment. As the environment changed during the Pliocene, marine diversity diminished for a while before natural selection caused new species to evolve and thrive. Unfortunately, this would have taken thousands and thousands of years; time that the megalodon did not have. With less biodiversity,  and animals to eat, all predators in the ocean would need to compete for similar food sources. The prey that megalodon once thrived on would have diminished,  which meant that either they had to compete for a different food source or starve to death. Before the change in the environment of the Pliocene, the oceans were filled with large marine animals. Many of these animals ate krill or small fish like the baleen whales of today. This meant that there was an abundance of prey for megalodon to hunt. However, after the climate shift organisms such as toothless walruses, aquatic sloths, and dwarf baleen whales did not survive in the new environment. Slowly, but surely, the megalodon’s variety of food was diminished. This is where the real problem for megalodon came in. Changing of climate most likely contributed to the extinction of the species, but scientists now believe there was one main culprit that drove the nail into the coffin of the megalodon. At around the same time as megalodon went extinct,  a new apex predator had just started to make its appearance, the great white shark. Carcharodon carcharias, or the great white shark, appeared around the same time as the megalodon species began to decline. It would seem this new species of shark could outcompete the megalodon. The smaller size of great whites allowed them to catch and eat the smaller prey, which was more abundant after the climate shift. The ability to eat many different species,  other than just small whales, gave the great whites an advantage. Not only did the great white have a wider variety of food it could choose from,  but the smaller body size actually worked in its favor. Since the megalodon had such a massive body it needed to stay in relatively warm waters, so that it could maintain its body temperature. Sharks are ectotherms meaning that they don’t regulate their internal body temperature,  but instead, rely on factors such as sunlight and muscle movement to increase the temperature of their bodies. The smaller bodies of the great white sharks meant they could venture into cooler waters since they had less body mass to keep warm. Their muscles did not need to work quite as hard as megalodon to keep their body temperature up, and therefore,  they didn’t need as much energy from food as their larger cousins either. It was also likely that great whites hunted some of the same prey as megalodon. Perhaps the great whites targeted the young of the species that megalodon was hunting,  thus reducing the amount of adult prey available for the megalodon to eat. The great white sharks were by no means trying to outcompete and cause the megalodon to go extinct, but they were,  and still are, very efficient predators, who in the new ocean environment thrived. The great white shark’s success most likely played a role in the extinction of the once-great megalodon.
Scientists also think that the evolution of other smaller species of shark could have put pressure on the megalodons. For example, tiger sharks which lived during the same time as the megalodon,  and in very similar environments, may have contributed to the larger shark’s demise.  It has been suggested that great whites and tiger sharks may have fed on megalodon young that had not grown to their full size yet, causing even fewer numbers of the species to reach maturity. As we gather more evidence, we may find that megalodon was not just outcompeted by smaller species of shark, but their babies may have been hunted by them as well. One theory of what caused the megalodon to go extinct is really out there,  literally. Some astronomers suggest that a supernova may have contributed to the extinction of the largest sharks that ever lived. The claim is that a nearby star went supernova,  enveloping the Earth in harmful muon radiation. This radiation would have been harmful to many species. But ones that reproduce slowly like the megalodon, would have been affected much more drastically because of the build-up of mutations and lack of genetic diversity in the species.
All of these factors may have played a role in the extinction of megalodon,  but are we so sure that the species is really extinct? Could there be a gigantic 60-foot shark lurking in the blackness of the oceans? Well, let’s look at the evidence. Humans have been exploring the oceans, and recording their observations, for hundreds of years. In all that time there have been no reliable accounts, or documentation, of megalodons, being sighted. If megalodons were still alive, we would at least expect to find whales or other prey with 10-foot bite marks on them from the jaws of a megalodon. But such evidence has never been found.  We would also expect to find at least some megalodon fossils in layers of the Earth younger than 3.5 million years old, but to this day no such fossils have been found. Scientists also believe that megalodons established nurseries for their young in shallow seas, which means that we should see baby megalodons near the surface of the ocean.  Even a baby megalodon would be a massive shark, and would most definitely make the news. Yet,  this has never occurred. It is important to remember that for any species to continue on it needs to reproduce, and megalodons, like all sharks and animals, don’t live forever.  The fact that there has never been a reliable sighting of a full-grown, or baby megalodon, is a good indication the species went extinct long ago. Megladon also likely hunted in shallower waters or near the surface,  because that was where their food source lived. Whales are mammals, and therefore need to come to the surface to breathe air. It would seem highly improbable that a megalodon would wait until a  whale dove into the far depths of the ocean to attack it. For one thing, how would the megalodon see its prey in the deep ocean where no light reaches? Sharks have a very keen sense of smell,  but they still rely heavily on their eyes to attack prey once they are within sight. So, no, there is no more megalodon left in the oceans of planet Earth. And to be fair, it’s probably better that way. I don’t know about you, but I would be much more hesitant to go swimming or get in a boat if I knew there was a fifty-foot killing machine swimming around the ocean.
