He is a paleobiologist at the University of Bristol in England. This study seeks to link tooth, jaw and body size in fossils of extinct lamniform sharks, says Humberto Férron. Finally, a large, fattened shark emerges from its mother and swims away. As that baby packs on the pounds, its body temperature rises. As she eats more, her waiting-to-be-born pup grows bigger. Its constant feeding also forces its mom to eat more. How does it work? Once the first shark pup hatches inside its mom, it begins gobbling up the remaining eggs. So Shimada and his colleagues reasoned that ancient ones like megalodon did too. Unlike other sharks, lamniforms practice intrauterine cannibalism. This takes a gnarly turn in living lamniform sharks. But the mother squirrels them away in her womb until they are ready to hatch. Sharks embryos instead develop inside the eggs. Males then come by and fertilize those eggs. Most female fish lay eggs outside their bodies. It could have affected megalodon’s size and body temperature. Their novel idea: Competition for food in the womb.

Shimada and his group say something else must have been at play.

Mark Kostich/iStock / Getty Images Plusīut that theory doesn’t explain why these sharks were warm blooded in the first place. This lets it grow big and strong before leaving the womb and being “born.” Scientists now suspect this could have put such species on the path to warm-bloodedness - and ultimately gigantic body sizes. The first pup to hatch inside mom eats up the other eggs. Both sharks belong to a group with a unique reproductive strategy. Megalodon tooth (left) is far larger than that of a great white shark (right). More and bigger food may have allowed these sharks to get bigger. Warm-blooded sharks also need more food than slower moving, colder-blooded ones. By regulating their body temperatures, they can swim faster to catch large, speedy prey in cold waters. Extinct and modern lamniforms are more warm-blooded than other sharks.

Warm-bloodedness - or endothermy - may be one key. Gigantism also occurs in several modern lamniform species.Įxactly why megalodon and its cousins became so big is still a bit murky. That means they also exhibited “gigantism.” While that’s not as titanic as megalodon, it’s still pretty big. Four other extinct species of lamniforms grew to more than 6 meters (20 feet). Scientists concluded megalodon was at least 14 meters long. And those choppers can tell a story of extinct species. These remain behind when a shark goes belly up. Unlike bone, cartilage doesn’t last long once an animal dies. That’s because shark skeletons are made of cartilage. It wasn’t easy for scientists to figure out its body size.

But throughout history, there have been more than 200 lamniform shark species. They include the great white, mako and basking sharks. The researchers focused on lamniforms, also known as mackeral shark. Scientists used these teeth to estimate the body sizes of fish. Shimada’s team came up with its cannibalism idea after analyzing modern and ancient shark teeth. They were twice the size of a double-decker bus and half as large as today’s whale sharks, filter feeders that can grow to 30 meters (100 feet). Their constant chowing down allowed these ancient beasts to become the largest shark ever to hunt the Earth’s oceans. Along with some colleagues, he came up with this out-of-the-box theory: The adults’ size may reflect the appetites of megalodon babies in the womb. As a paleobiologist, he studies ancient animals. Kenshu Shimada works at DePaul University in Chicago, Ill. What ‘The Meg’ doesn’t quite get right about megalodon sharks Scientists think megalodon and some other ancient sharks did it too. Some of megalodon’s living relatives do this, such as great white sharks. It means the strongest embryo in the womb devours its weaker siblings. They call it intrauterine (In-trah-YU-tur-in) cannibalism. How did this creature get so ginormous? A group of scientists now suspects part of the reason may be that megalodon ate its siblings while still in its mother’s womb. No other predatory shark has matched its size and ferocity. The 14-meter (45-foot) carnivore with razor-sharp teeth cruised the seas some 23 million to 2.5 million years ago. Otodus megalodon is a giant among sharks.

Beasts of prey cannibals