Giant ancient sharks’ huge babies ate their siblings in mother’s womb

The Megalodon, which became popular with the 2018 film The Meg, is the largest predatory shark ever discovered and remains a bit mysterious. It lived between 15 and 3.6 million years ago and was at least 14 meters long, more than twice the height of a large adult great white.

Only a few parts such as teeth, skull, and spine of the shark’s body are mineralised and preserved because of its soft cartilaginous skeleton. Hence, the fossil record for this shark is very poor.

Not surprisingly, researchers paid close attention to the predator’s 17cm teeth. In a recently published study, DePaul University professor Kenshu Shimada and his colleagues looked elsewhere for clues.

The team examined the spine of the now-extinct Megalodon to find that it gave live birth to two-meter-long babies that were larger than the average adult human. The big size of the babies was likely due to the cannibalism, eating their unhatched siblings in the womb.

Just like humans, sharks also have a spine made up of many components called vertebra that grow as the animal ages. The researchers measured the vertebra of a Miocene epoch megalodon, which lasted from five to 23 million years.

The team compared it to modern great white sharks and estimated that the megalodon it came from was around nine metres long during its lifetime. Sharks put rings of hard tissue on their vertebra every year and, like a tree trunk, they can be used to estimate age.

The sientists would have had to cut the fossil and damage it forever in order to count those rings inside. The solution was to examine the internal structures using detailed X-ray scanning without damaging the valuable specimen. And it was revealed that this shark died at the age of 46.

By looking through the layers, the team was able to see the huge size of this vertebra when the shark was born. Surprisingly, the estimate of the size of the first growth ring implies that the shark was two metres when born, meaning that it was bigger than the average adult human at birth.

Some sharks lay eggs while others give birth. However, in most sharks, the eggs hatch in the womb of the mother, where the young feed on the egg yolks and fluids she secretes until they hatch.

Image credits: A reconstruction of the megalodon shark. (Photo: Luis Alvaz/Wikimedia CommonsCC BY SA 4.0)