Megalodon: The Giant Prehistoric Shark and Its Extinction

Megalodon (Otodus megalodon) was a giant shark that lived in the world’s oceans from about 23 million to around 3.6 million years ago. Known mainly from enormous fossil teeth, it is the largest predatory shark ever discovered, with most estimates putting the biggest individuals at roughly 15 to 20 metres long. It preyed on whales and other marine mammals before disappearing in the early Pliocene, probably as a result of changing climate, prey and competition.

Background: a world of warm seas

Megalodon appeared in the early Miocene, when the oceans were generally warmer than today. Whales, seals and sea cows were diversifying, and coastal seas offered abundant large prey.

It belonged to the family Otodontidae, a line of large sharks that had grown steadily bigger over tens of millions of years. Its forerunners included Otodus obliquus and species often grouped as Carcharocles, whose teeth show a gradual increase in size and the development of fine serrations. Megalodon was the last and largest member of this line.

The name means “big tooth”. For much of the twentieth century megalodon was placed in the genus Carcharodon with the great white shark, and later in Carcharocles. Today most researchers use Otodus megalodon, reflecting the view that it descended from earlier otodontid sharks rather than from the ancestors of the great white.

Discovery and the fossil teeth

Tongue stones

Fossil shark teeth have been collected since antiquity. In parts of Europe, notably on Malta, they were called glossopetrae, or tongue stones, and were once thought to be petrified serpents’ tongues or stones that fell from the sky. Some were worn as amulets against poison.

In 1666 the Danish anatomist Nicolas Steno dissected the head of a large shark caught off the Italian coast. In a work published in 1667 he argued that tongue stones were in fact the teeth of ancient sharks, an important early step in understanding fossils as remains of living things. Many of the large tongue stones known in Europe came from megalodon.

The Swiss-American naturalist Louis Agassiz gave megalodon its scientific name in the 1830s, in his major study of fossil fish, Recherches sur les poissons fossiles.

What the teeth reveal

Shark skeletons are made of cartilage, which rarely fossilises. As a result, almost everything known about megalodon comes from its teeth and a few sets of vertebrae.

Megalodon teeth are triangular, thick and finely serrated. The largest exceed 17 centimetres along the slanted edge, about the size of an adult’s hand. Like all sharks, megalodon grew new teeth in rows and replaced lost ones throughout its life, which explains why its teeth are among the most common large fossils in the world.

Teeth have been found on every continent except Antarctica, in places as far apart as North Carolina, Florida, Peru, Chile, Malta, Japan and Australia. This distribution shows that megalodon ranged across most warm and temperate seas, especially coastal waters.

How big was megalodon?

Estimating the length of a shark known mostly from teeth is difficult. Researchers compare tooth size with that of living relatives, especially the great white shark and other mackerel sharks, and apply mathematical relationships between tooth height and body length.

An exceptional fossil from Belgium, a partial vertebral column of well over a hundred vertebrae, belonged to an individual estimated at around 9 to 11 metres. Studies of tooth size suggest that the largest individuals reached about 15 to 20 metres. A 2022 study produced a three-dimensional model of a 16-metre individual weighing more than 60 tonnes.

These figures remain debated. A 2025 study suggested that megalodon may have had a more slender, elongated body than once thought, which would change weight estimates and possibly allow lengths of over 20 metres for the largest individuals. Popular claims of 30 metres or more are not supported by the evidence.

Hunting and diet

Bite marks on fossil bones show what megalodon ate. Vertebrae, ribs and flippers of baleen whales, small toothed whales, seals, sea cows and sea turtles bear deep gouges and serrated scrapes that match its teeth. Some fossils from Peru and North America show bites on whale flippers and tails, suggesting attacks aimed at disabling prey.

Studies of its jaws suggest a very powerful bite. A 2008 computer model estimated bite forces of roughly 108,000 to 182,000 newtons, among the strongest of any known animal, although such figures are approximate.

Chemical analyses of fossil teeth, including nitrogen and zinc isotopes published in 2022, suggest that megalodon fed at an extremely high level in the food chain, in some cases higher than any living marine predator. A 2023 study of oxygen and carbon isotopes indicated that megalodon was partly warm-blooded, keeping its body several degrees warmer than the surrounding water, as some modern sharks do.

Nurseries and growth

In 2010 researchers led by Catalina Pimiento described a collection of small megalodon teeth from the Gatún Formation in Panama, dating from about 10 million years ago. They argued that the area was a nursery, a shallow, food-rich coastal zone where young sharks could grow while avoiding larger predators.

Studies of growth bands in vertebrae suggest that megalodon gave birth to large young, possibly around 2 metres long at birth, and that individuals may have lived for several decades. As in many modern sharks, the young were probably born live rather than hatched from eggs.

Extinction

Megalodon disappeared in the early Pliocene. A 2014 study by Pimiento and Christopher Clements estimated extinction at around 2.6 million years ago, but a 2019 reassessment led by Robert Boessenecker concluded that the youngest reliable fossils are about 3.6 million years old.

Several explanations have been proposed, and most researchers think they acted together:

• Climate change: The Pliocene saw global cooling and falling sea levels, which reduced the warm coastal habitats used for feeding and nurseries.
• Changes in prey: Baleen whales evolved larger sizes and began migrating to cold polar waters, where megalodon may not have been able to follow. Many smaller whale species also declined.
• Competition: The great white shark appeared around the start of the Pliocene and spread worldwide. Zinc isotope studies suggest that young megalodons and great whites fed at similar levels, so competition, especially for juveniles, may have contributed.

The rise of the Isthmus of Panama, which closed the seaway between the Atlantic and Pacific in the following few million years, also changed ocean circulation and marine life. Its role in megalodon’s decline is uncertain. On land, the same event led to the Great American Biotic Interchange.

Megalodon was not the only casualty. A 2017 study led by Catalina Pimiento identified a wider Pliocene marine megafauna extinction, in which roughly a third of the genera of large marine animals, including many marine mammals, seabirds, turtles and sharks, disappeared. Megalodon’s loss may therefore be part of a broader reorganisation of ocean life as the planet cooled toward the ice ages.

After megalodon vanished, the role of top ocean predator passed to animals such as the great white shark and, later, the orca. Some researchers have suggested that the absence of megalodon allowed baleen whales to evolve the gigantic sizes seen in species such as the blue whale, though this idea is still being tested.

Myths and facts

Myth: megalodon still survives in the deep sea. There is no credible evidence for this. Megalodon was a warm-water, coastal predator, not a deep-sea animal, and a population of giant sharks would leave abundant fresh teeth and be seen at the surface. Fictional documentaries suggesting otherwise have been widely criticised by scientists.

The survival myth is sometimes linked to teeth dredged from the Pacific sea floor by the British research ship HMS Challenger in the 1870s. Coatings of manganese on some of these teeth were once used to suggest they were geologically young, but the dating method was unreliable and the teeth are now regarded as ordinary fossils.

Myth: megalodon fought dinosaurs. Megalodon appeared more than 40 million years after the extinction of the non-avian dinosaurs and marine reptiles such as mosasaurs, which ended with the Chicxulub asteroid impact.

Myth: megalodon was the direct ancestor of the great white. Most researchers now place megalodon in a separate lineage, the otodontids. The great white’s closest fossil relatives are other sharks such as Carcharodon hastalis.

By the numbers

Timeline

• c. 23 million years ago: Megalodon appears in the early Miocene.
• c. 10 million years ago: Young megalodons use a coastal nursery in what is now Panama.
• c. 3.6 million years ago: Megalodon becomes extinct in the early Pliocene.
• 1667: Nicolas Steno publishes his argument that tongue stones are fossil shark teeth.
• 1830s: Louis Agassiz gives megalodon its scientific name.
• 2010: A megalodon nursery area is described from Panama.
• 2014: A study estimates extinction at around 2.6 million years ago.
• 2019: A reassessment pushes the extinction back to about 3.6 million years ago.

Why it matters

Megalodon shows how a top predator can dominate the oceans for millions of years and still vanish when climate, prey and competitors change. Its teeth, found worldwide, also played an early role in helping scientists recognise fossils as remains of ancient life. Like the earlier whales of Wadi Al-Hitan, it is a key part of the story of how ocean ecosystems took their modern form.