Megalodon was a giant shark. It lived in the sea a long time ago and died out about 3.6 million years ago. Most of its fossils are teeth, so it is hard to know its exact size. A 2025 study says it may have been up to about 24 meters long.

Why did it die out? The sea may have become colder, and its food may have changed. Also, great white sharks may have eaten similar food.

Megalodon was one of the largest sharks that ever lived. Because a shark's skeleton is made of soft cartilage, most megalodon fossils are teeth and a few backbones, so its size is hard to estimate. Earlier studies suggested that it was about 15 to 18 meters long.

However, a 2025 study compared its backbone with the body shapes of 165 kinds of sharks and suggested that it was slimmer and may have reached about 24 meters. Megalodon probably went extinct about 3.6 million years ago. Possible reasons include cooling oceans and changes in its prey, such as whales. A 2022 study also suggests that great white sharks sometimes ate similar prey, so competition for food may have played a role.

Megalodon, among the largest sharks ever to exist, is known mainly from teeth and occasional vertebrae, because shark skeletons are made of cartilage that rarely fossilizes. Size estimates therefore depend heavily on assumptions. Traditionally, researchers scaled its teeth using the stocky proportions of the great white shark, arriving at about 15 to 18 meters. A 2025 study instead compared vertebrae with the body forms of 165 living and extinct sharks and proposed a slimmer animal reaching roughly 24.3 meters and 94 tonnes, cruising slowly at 2.1 to 3.5 kilometers per hour, though the authors themselves described these figures as working hypotheses, and the slender-body model remains disputed.

Chemical analysis of teeth published in 2023 indicates that megalodon was warmer than the surrounding water, an advantage for speed and range but one that demanded enormous amounts of food. That dependence may have proved fatal. A 2019 reassessment of fossil dates placed its extinction at around 3.6 million years ago, earlier than a 2014 estimate, and scientists point to cooling seas, shifting prey, and competition: zinc isotopes suggest that great white sharks at times fed at a similar level of the food chain. None of these factors, however, has been proven decisive.