Megalodons are the topic of conspiracy theories, speculation, and debate among friends around the world. The primary question everyone wants to know, though, is are they still alive?
Fossils of megalodon teeth and jaws help scientists estimate their size at 16-18 m when fully grown. Since sharks have cartilage rather than bones, full skeletons do not exist. Megalodons belonged to the order of sharks known as Lamniformes or mackerel sharks. Other notable species of mackerel sharks include great whites, goblin sharks, and megamouth sharks. Those within this classification have similar characteristics, such as being fast swimmers, giving birth to live young, and living up to 1300 m deep (remember this for later).
Megalodons went extinct from the fossil record about 3.7 million years ago, meaning no specimens have been found that would put their age younger than this. Boessenecker (2019) states that they were first seen around 5.6 million years ago during the late Miocene era and left during the early Pliocene.
While the exact cause for megalodon extinction is somewhat unknown, fossil records give us a better idea. Due to the lack of evidence supporting climate and geographical changes as the reason for their extinction, it is believed that the evolution of other species led to their downfall. Sperm whales and killer whales both evolved as apex predators similar enough in size to the megalodon that they likely competed for food. The great white sharks that still roam our oceans also evolved at this point, changing from having non-serrated to coarsely serrated teeth (smooth edges to jagged edges), which gave them better hunting abilities. The first appearance of modern great white sharks overlaps with the megalodon extinction. Adult great whites were about the same size as young megalodons, and because the two likely ate the same prey, great whites could have been eating the megalodons dinner.
I often hear the argument that megalodons still exist, but simply evolved to live in deeper water. With their massive size, they would have needed much more food that what is available in the deep ocean. Additionally, all evidence shows that they preyed on animals in a similar manner as great whites- they were shallow water hunters. If a shark longer than a greyhound bus was still alive today (and there would have to be enough of them to reproduce), not only would we see these animals via boat, plane, cruise ship, even wave-watching from shore, but we would also see their impact. The food sources they were eating would be heavily affected. Perhaps the strongest evidence, though, is that there is not a single fossil of them that would make them younger than 3.2 million years old. So, to answer the original question: no, megalodons are not roaming our waters today.
Boessenecker, R. W., Ehret, D. J., Long, D. J., Churchill, M., Martin, E., & Boessenecker, S. J. (2019). The early pliocene extinction of the mega-toothed shark otodus megalodon: A view from the eastern North Pacific. PeerJ, 7. https://doi.org/10.7717/peerj.6088