The megalodon was one of the largest creatures ever to exist on Earth. It was the largest known predator, as well as the largest known fish ever to exist. Specifically, the megalodon was a species of shark, which was so fierce and massive that many people express fear and fascination toward it, despite the fact that it has been extinct for at least 2.6 million years. It is most often compared to a hypothetical, much larger version of the extant – or still living – great white shark. While scientists cannot be certain what the megalodon ate, they have been able to make some inferences. For this, they have used fossils of the megalodon and other animals found nearby, as well as geological records about the time periods for the locations where the fossils have been found. They have also used information about the eating habits and other behaviors of similar sharks that exist now.

Megalodons lived from the middle of the Miocene epoch to the Pliocene epoch, which places their existence approximately between 16 million years ago to 2.6 million years ago. There are widespread theories held by the public that megalodons could still exist in the uncharted depths of the oceans. These ideas are partially fueled by sensationalized information in popular media. They are also fueled by the discovery of another sea creature, one that was long-believed to be the stuff of scary stories but not real. For thousands of years, sailors have told stories about giant squids attacking their ships, or swimming alongside them, equalling the length of their vessels, or battling whales. Sometimes squid corpses or body parts would even wash up on shores. No one had ever seen a live, giant squid, however, so it did not seem like anything more than a myth until the beginning of the 21st century, when new technology allowed marine biologists to capture images of live, healthy adult giant squids in the deep ocean. People reason that if the ocean is mostly uncharted and can hide such giant creatures for so long, perhaps it can also hide megalodons (for more information about giant squids, see the Resources section).

The theories about megalodons still lurking in the ocean, however, have been scientifically disproven. Paleontologists and marine biologists have used an approach known as optimal linear estimation, or OLE. Using OLE, the scientists gathered the data on all the the megalodon fossils that have been found. They then input the ages of each fossil, or in other words, approximately when the individual shark it belonged to lived. From there, they were able to analyze the distribution of the gaps in time between the found fossils. Using this method, they ran repeated simulations to determine the most statistically likely date of extinction for megalodons. While it is possible for optimal linear estimation to provide a date in the future, as it would for humans or any other still living species, 99.9 percent of the simulations for megalodons provided an extinction date in the past. For the scientists who study megalodons and related species, this is sufficient evidence to reject the possibility that megalodons still live anywhere on the planet.

The means by which megalodons went extinct is less clear, however. Most of what scientists know about megalodons has been pieced together from partial evidence and computer models, with the help of knowledge about related, modern species. Scientists' limited information, however, is not enough to help them explain with certainty why megalodons went extinct. Instead, they have hypotheses. For example, one hypothesis has to do with oceanic climate. Megalodons raised their young near coastlines, and adult sharks, as well as many other types of other marine life traveled through the Central American Seaway, which was a water passage that separated North America and South America. Since then, the continents have shifted, so the landmasses looked somewhat different than they do now. During the last million years of the megalodons’ existence, the oceans where megalodons spent much of their time were increasing in depth and decreasing in temperature.

In addition, the oceanic currents between the Atlantic and the Pacific shifted, creating beginning of what is today known as the Gulf Stream, pushing the Atlantic currents northward and dropping water temperatures. This may have contributed to megalodons’ extinction, since they could not leave the water and tended to live, hunt and birth their young in shallow, warm waters. Not only did the climate change make the oceans less livable for the megalodons, but it affected the lives of their prey. There is evidence that the prey species that megalodons relied on for their large daily caloric intakes moved into colder oceanic climactic zones and managed to thrive there, while the megalodons were unable to do the same. This, too, led to a drastic population decrease of megalodons, and combined with the darkening, deepening, cooling waters, may have prevented them from eating, reproducing and perpetuating their species.

Megalodon was a cosmopolitan species, which means that it successfully thrived all over the world. Its fossils have been found all over the planet, although they favored moderately warm ocean regions, especially those somewhat close to coastlines. The majority of these fossils have been megalodon teeth, which measure up to 7 inches in length. Many of the teeth, as well as other shark teeth and other marine fossils, have been found buried in a privately owned hill called Shark Tooth Hill near Bakersfield, California, in an area that was at the bottom of the ocean during the Miocene epoch. Like modern sharks, the megalodon’s skeleton was not made of bones, but of cartilage, which is a softer kind of tissue, and which does not typically fossilize over millennia for scientists to find. Some exceptions were fin cartilage and spinal vertebrae. The megalodon’s teeth were full of calcium and other mineral deposits, however, which made them ideal fossil candidates. Through computer models and knowledge about the anatomy of extant large sharks, the skeleton, jaw, physiology and even some behaviors of the megalodon have been extrapolated from the tooth fossils alone.

The great white shark is a modern, living shark, notorious for its depiction in the film "Jaws," directed by Steven Spielberg. The largest recorded great white shark was 6 meters (19.7 feet) long and 2.5 meters (8.2 feet) high. In comparison, the megalodon could grow up to 49 to 60 feet long and 19.7 to 23 feet high. While the modern-day sperm whale can technically take the title for the largest predator species to ever exist because it is a few feet longer than the megalodon on average, the megalodon is the largest predator species by weight; it weighed 50 to 70 tons. For further comparison, the great white shark swims at approximately 25 miles per hour and the megalodon, which is considerably larger, swam at about 20 miles per hour, a very high speed for such a massive creature. While a fish this size swimming at that speed is frightening to many people, what’s the fastest fish in the world? A fish called the sailfish, which swims at almost 70 miles per hour, far speedier than either shark.

Megalodon teeth have been found by paleontologists and non-scientists – even beachgoers have stumbled upon them – all over the world, sometimes individually turning up on digs. They can be sharp enough after millions of years to still cause wounds that require medical attention and sutures. Even though shark attacks on humans are rare, these sharp teeth and the fact that sharks do prey on sea animals are likely reasons that people’s fears rest so much on sharks, and less on the chance that a whale eats a person. Sometimes they are found near other marine life fossils, and sometimes they are embedded in other marine fossils, like whale bones, suggesting that the shark bit a whale and lost the tooth in the process. Other marine vertebrate fossils show deep, large serrated scratch marks that indicate the large teeth (megalodon comes from the Greek root words for large and tooth) of a megalodon as the culprit. What paleontologists have never found is an entire set of teeth, much less an entire jaw.

The teeth that have been found were enough for scientists to construct synthetic megalodon jaws, some of which are on display in science museums. When the jaw is in an open position, a human can easily step through, most without even needing to crouch. The megalodon jaw opened approximately 10 feet and had the force to crush an automobile. Using simulations on the computer and even using jaw models, megalodon experts have been able to build a understanding of how the species used their jaws, what the musculature around their jaws must have looked like, and how that extended to the rest of their bodies. From a few teeth, they have been able to determine the anatomy of a shark that went extinct long before humans arose on Earth.

Because of megalodons’ massive size and speed, they had very high caloric needs, and were required to eat between 1,500 and 3,000 pounds of food each day. While scientists cannot be certain about megalodons’ diets, the widely held belief is that they hunted large marine vertebrates in order to obtain the maximum amount of calories per kill, and to reserve energy. It would not be efficient for megalodons to hunt small prey all day long. Still, megalodons had their pick of sea creatures to eat. They could eat a variety of animals because of their speed and enormous jaws with double rows of sharp teeth.

The most likely prey for megalodons was cetaceans – this is the order of animals that includes whales, dolphins and porpoises. Marine paleontologists are uncertain exactly which species of whales megalodons preyed on; for instance, did megalodons attack whales significantly larger than themselves? It was possible that they rose quickly through the ocean water, slamming into large whales at the surface before they could react, and stunning them before biting them. It is also possible that they bit off their fins so they could not escape, like some modern-day sharks do. Some modern sharks hunt in packs, and megalodons may have as well. In addition to whales, dolphins and porpoises, megalodons likely preyed on many other large marine vertebrae, such as smaller sharks and other large fish and giant sea turtles. One likely order of prey is pinnipeds, which includes seals, sea lions and walruses.

The megalodon was an apex predator; this means that the species was at the top of its food chain, carnivorous, ate other predators and had no predators. Some modern-day apex predators include the great white shark, the lion and gray wolves. While the megalodon did not fear predation from other animals, it may have faced other threats from other animals. As the climate change diminished megalodon population size while much of the prey moved to colder regions, it likely had competition for prey from other predator species, such as ancient killer whales and sperm whales. This may have hastened its extinction. Other, smaller sharks were probably quick to take its place in the food chain.