What Was Megalodon? The Largest Shark That Ever Lived, and Why It Is Gone

A shark sheds teeth continuously through its life and grows new rows behind, so a single animal leaves thousands, and megalodon's are found in marine rocks of every continent except Antarctica from about 20 to 3.6 million years ago. The largest exceed 17 centimetres in slant height. Their shape, a broad triangle with fine serrations and a thick root, is built for cutting through blubber and bone, and bite marks matching them are found on the fossil bones of whales, dolphins, seals and turtles, sometimes with the tip of a tooth still lodged in the bone. From the teeth, and from a few fossilised vertebrae and, in 2022, a set of vertebrae from Belgium that gave the proportions of a spine, palaeontologists reconstruct the animal by comparison with living sharks, and the comparisons are where the disagreement starts.

The traditional method scales the great white, whose tooth size and body length are known, up to megalodon's teeth, and gives 15 to 18 metres, with the largest individuals perhaps 20, and a weight of 50 to 70 tonnes. That assumes megalodon was shaped like a great white, which it may not have been. A 2024 study of the Belgian vertebrae argued that the animal was longer and slimmer, more like a mako or a lemon shark stretched out, perhaps 24 metres, while others read the same bones as supporting a stockier build; the question is open because no complete skeleton exists and never will. What is agreed:

• •It was at least three times the length of the largest great white and probably an order of magnitude heavier
• •Its jaws opened about two metres wide and its bite force, estimated at 100,000 to 180,000 newtons, was the strongest of any animal known
• •It was warm-blooded in part, as great whites are, keeping its muscles above the water temperature, which the isotopes in its teeth confirm
• •Newborns were about two metres long, and nursery areas in shallow bays, where only juvenile teeth are found, have been identified in Panama, Spain and the eastern United States
• •It is not a giant great white: it belongs to a separate lineage, the megatooth sharks, that split from the great white's ancestors tens of millions of years earlier

Megalodon appeared about 20 million years ago in warm seas full of the whales that had recently become large, and it was their predator for fifteen million years. The bite marks show it attacked the flippers and tails of whales to disable them and then the chest, as great whites do with seals, and the tooth chemistry places it at the very top of the food web, above anything else in the ocean before or since. A fifty-tonne shark needs a great deal of food, on the order of a hundred kilograms a day, and the warm coastal waters where the whales fed were where it lived; its teeth are rare in the deep ocean and absent from the cold seas of high latitudes, which is one of the clues to what happened to it.

It disappears from the record about 3.6 million years ago, and the causes that are argued over are not mutually exclusive. The oceans cooled as the Pliocene ended and the ice ages began, sea levels fell, and the warm shallow shelves and nursery bays shrank, removing the habitat where the young grew up. The whales it ate moved into the cooling polar waters, where it could not follow, and grew larger and faster. And the great white, which appeared in its modern form about four million years ago, competed with juvenile megalodons for the same medium-sized prey; the isotopes in the teeth of the two species overlap, suggesting they were eating the same things. A giant specialist with a slow reproduction rate, dependent on warm water and large prey, met a cooling planet and a smaller, more adaptable rival, and it is gone.

The claim that megalodon survives in the deep ocean, made by a 2013 television programme presented as a documentary and repeated by every film since, is false, and the evidence is the absence of everything. A shark that size would shed teeth by the thousand, and no megalodon tooth younger than 3.6 million years has ever been found, in any ocean, on any beach or in any deep-sea core. It could not live in the deep sea, which is cold and nearly empty of the whales it needed. It would leave bite marks on modern whales, which carry the scars of orcas and great whites and nothing else. The ocean is large and poorly explored, and it is not large enough to hide a fifty-tonne predator that had to eat a whale a week. Megalodon is the most impressive animal that the fossil record has to show for the age of whales, and the whole of its existence is in the teeth.

The fossil teeth long called tongue stones played a part in the history of science. In 1666 the Danish anatomist Nicolas Steno, working in Florence, dissected the head of a large shark caught off the Italian coast and saw that its teeth closely matched the tongue stones found in rocks far inland. He argued that they were the teeth of ancient sharks, and then asked how solid objects could end up inside solid rock. His answer, that the rock had formed as layers of sediment around them, led him to principles still taught in geology today, including the idea that lower layers are older.

The teeth survive so well because of what they are made of. Shark teeth are covered in a hard, mineral-rich layer and contain a great deal of calcium phosphate, which resists decay far better than cartilage. As a tooth lies buried, minerals from the surrounding sediment and groundwater seep into it, and these give fossil teeth their colours: black, grey, brown, blue or orange depending on the local chemistry, such as iron or manganese. The colour therefore tells you about the place where the tooth was buried rather than its age. Freshly shed teeth from living sharks are white, one clue that a tooth is modern.

The teeth also record how megalodon came to be. Its lineage, the megatooth sharks, can be traced back more than 50 million years through a sequence of species whose teeth change step by step. The oldest, Otodus obliquus, had large teeth with smooth edges and a pair of small side points, called cusplets, at the base. Later species developed serrated edges while keeping the cusplets, and in the species just before megalodon the cusplets shrank. Megalodon's adult teeth lost them altogether and became broad, fully serrated triangles. Because the changes accumulate within one line, the megatooth sharks are a classic example of evolution recorded in a continuous fossil series.

That continuity is also why the shark's scientific name keeps changing. The Swiss naturalist Louis Agassiz named it Carcharodon megalodon, big tooth, in the 1830s, placing it beside the great white. Later researchers, convinced that the two belonged to separate lineages, moved it to a genus called Carcharocles, and many now place it in Otodus with its oldest ancestor, reasoning that a single evolving line should not be split into genera at arbitrary points. You will meet all three names in books and museums, and they refer to the same animal; the argument is about how to classify a lineage, not about the shark itself.

Megalodon's diet is known partly from the bones of its prey. Fossil whale bones from several parts of the world carry deep gouges and scratches that match the serrated edges of megalodon teeth, sometimes with broken tooth fragments still embedded. Some show signs of healing, meaning the whale survived the attack.

Analyses of these marks suggest that megalodon often targeted the flippers, tails and ribcages of whales, perhaps disabling them before feeding or attacking the chest to reach vital organs. Chemical studies of its teeth, comparing zinc and nitrogen isotopes, also indicate that it fed very high in the food chain. Together, the evidence paints a picture of a predator that specialised in large marine mammals.

Megalodon was a shark of the megatooth lineage, 15 to 20 metres long and perhaps more, that hunted whales in warm coastal seas from about 20 to 3.6 million years ago and is known almost entirely from its hand-sized serrated teeth, since a shark's skeleton is cartilage. It died out as the oceans cooled, its nurseries and prey moved away, and the newly evolved great white competed with its young, and the total absence of any younger tooth means it is certainly not alive.