The Real Reason Megalodon Got So Gigantic (and Then Went Extinct)

The surprising science behind the ocean’s largest shark — and why it couldn’t last

As some readers know, I was fortunate to do my PhD research in the land down under in Australia. 

If you want a comical representation of Australian culture, I strongly recommend you read In a Sunburned Country by Bill Bryson. One of the things that the book captures best is the Australian normalization of having sharks on the beach. It may sound surprising, but it’s not uncommon to hear someone explain that “it’s been ages since the last shark attack, right? What’s it’s bee? Like, three weeks or so?”

And of course, you never forget the first time that, while relaxing on the beach, you hear over the megaphone: “There’s a shark in the back, please stay clear.” They call it Tuesday. 

One breezy afternoon, as waves gently rolled onto the shore on the coast of Manly, north of Sydney, I stared into the endless blue while hearing, once again, the scary message in the background. As a biologist, paleontologist, and ecologist, I’ve always been fascinated by the ocean’s secrets. And sharks are quite mysterious. 

I remember clearly how, back then, the idea of something like the mighty megalodon cruising those waters felt both thrilling and unimaginable. Now, a recent study sheds light not just on the size of this ancient giant but also on why certain marine animals grow so massive while others can’t.

Megalodon, scientifically known as Otodus megalodon, dominated our oceans roughly between 15 and 3.6 million years ago. Yet, despite its fame, this prehistoric shark remains enigmatic, mainly because fossils beyond teeth, scales, and scattered vertebrae are exceptionally rare. Paleontologists, traditionally picturing megalodon as simply a beefier, oversized version of today’s great white shark, now have reasons to rethink this image entirely.

A global team of shark and fossil experts, led by Dr. Kenshu Shimada of DePaul University, published their findings, bringing fresh eyes to old bones. 

They tackled a long-standing question paleontologists have been asking: How large was the largest megalodon? To find answers, the researchers carefully analyzed a nearly complete vertebral column fossil from Belgium, 11 meters long but missing the shark’s head and tail. 

Comparing proportions of 145 modern and 20 extinct shark species, they estimated that this particular megalodon reached about 16.4 meters (54 feet). Yet even more impressive is their upper-end estimation of 24.3 meters — around 80 feet — if using vertebral evidence from a specimen found in Denmark. 

Dr. Shimada underscored the significance: “The length of 24.3 meters is currently the largest possible reasonable estimate for O. megalodon that can be justified based on science.”

Reflecting on my experience in marine ecology, the study’s explanation of why certain aquatic vertebrates can reach such immense sizes fascinated me most. The team discovered that the megalodon’s body shape likely resembled not the iconic great white shark but today’s lemon shark, a more streamlined, slender-bodied shark. 

This slender body plan turned out to be crucial for aquatic gigantism. Like sleek racing cars built for speed and efficiency, slender-bodied sharks glide through water with less resistance, while bulky bodies face more significant drag. This means that though great whites can grow impressively large, reaching around 7 meters, their stockier builds impose natural limits.

The new body shape insights also help paint a clearer ecological portrait. At around 24 meters, megalodon weighed roughly 94 tons — comparable to today’s largest whales. Despite its enormous size, its estimated cruising speed was surprisingly slow, between 2.1 and 3.5 kilometers per hour, similar to modern great whites. 

This highlights how even the most significant predators may rely more on ambush hunting than rapid pursuits.

However, Dr. Shimada’s team didn’t just focus on size; their work also illuminated details about megalodon’s growth and reproductive biology. For example, by examining vertebral growth bands, they determined that megalodon pups were born at impressive lengths of nearly 4 meters, already dwarfing most modern sharks at birth. 

This suggested live birth with embryos feeding on eggs within their mother’s womb, a behavior seen in some modern sharks today, like the sand tiger shark. Interestingly, despite their huge size at birth, these newborns might not have required the nursery areas that smaller shark species typically need for protection, challenging previous assumptions.

Finally, the team’s insights touched on megalodon’s extinction. 

I know some of you may have made it here for this exact question. 

Their analysis hints at competition playing a significant role, particularly from the ancestors of today’s great white sharks, which emerged about 5 million years ago. As climates cooled and marine ecosystems shifted, prey populations like whales and other large marine mammals dwindled, intensifying competition. 

Under these pressures, the more efficiently built, though smaller and agile, great white sharks likely edged out their colossal relatives, ultimately contributing to megalodon’s extinction.

Reflecting on those days spent exploring the shores and teaching about marine life, studies like this constantly reinforce my belief in the importance of understanding past lives to better protect today’s marine ecosystems. 

Gigantic animals, whether extinct or alive, teach us about biological boundaries, adaptation, and resilience. The story of the megalodon isn’t just about size; it’s about efficiency, adaptation, and survival in a changing world. And though the megalodon vanished long ago, its story continues to swim through our imaginations, guiding us toward deeper questions about how life thrives in our oceans, both past and present.

Published in Fossils et al. Follow to learn more about Paleontology and Evolution.

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I’m thrilled you’re here. Stay curious, and thank you for sharing this journey with me!

Best,

Sílvia P-M, PhD Climate Ages

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