The Biggest Animals Ever: 5 Giants from the Ocean

A mosasaurus hunts in prehistoric oceans
© Dotted Yeti/

Written by Heather Hall

Updated: July 1, 2023

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The largest animal in the ocean is the Blue Whale.

Hundreds of years ago, something peculiar happened… 

People started finding dragon teeth along the creeks and the shores of oceans. Big, six-inch-long dragon teeth. 

How could that be possible? Well, today we know they were really finding teeth from megalodon (Otodus megalodon), the largest shark to ever live. But, was the megalodon the largest sea creature? Let’s find out!

Megalodon (Carcharocles megalodon)

Megalodons may have been 20 to 50 times the size of the largest great white sharks today.


Just how impressive was the megalodon? For starters, the shark may have been 20 to 50X the size of today’s largest great white shark. And, no, that’s not a typo. While the largest great white sharks found today weigh about 5,000 pounds…

‘Conservative’ estimates of megalodon’s size place its maximum size at 47,960 kg (105,733 lbs). Larger maximum size estimates place megalodon’s highest potential weight at 103,197 kg (227,510 lbs). 

( For perspective, a single megalodon was the weight of about 1,250 fully grown adults!)

Just this week, brand-new research was published on megalodon. 

The incredible conclusion? There’s simply no other predatory shark that’s comparable. 

The largest other sharks in the megalodon’s ‘order’ reached just 7 meters (23 feet), just half the megalodon’s length and a fraction of its weight. This led the authors of the study to declare megalodon had “off-the-scale gigantism.”

Translation: there’s simply no shark we’ve ever found fossil evidence of that compares to megalodon. It’s 10 times, 20 times, and even 30X the mass of all other related sharks! 

Yet, the megalodon was far from the only ancient ‘giant of the deep’ that scientists have uncovered. Below, you’ll find 5 different giants of the sea that sometimes could be even larger (and potentially even more deadly predators) than megalodon itself!

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Megalodon vs. Mosasaurus

A mosasaurus hunts in prehistoric oceans

The genus Mosasaurus was a group of reptiles from the Cretaceous period.

©Dotted Yeti/

In the Cretaceous period (145.5 to 65.5 million years ago), a species of simply massive aquatic lizards roamed the world’s waterways.

The genus Mosasaurus was a group of reptiles that became apex predators during this time and grew to lengths recent estimates (Grigoriev, 2014) place at 56 feet. At the time, the Mosasaurus wouldn’t have encountered any sharks nearly the size of the megalodon, although they would have had plenty of competition from other apex predators of the time such as Plesiosaurus. 

The Mosasaurus had 250 teeth, and scientists estimate its bite force at around 13,000 to 16,000 psi. The size of their jaws would have made them predators of smaller sea animals than the megalodon. They would have used ambush tactics to take their prey by surprise on the surface of the deep.

Wondering who would win in a fight between pitting megalodon vs. Mosasaurus? We compared the two animals and which would win in a battle. It was a nail-biter, but one of these two deep-sea giants came out on top!

Megalodon vs. Livyatan 

Megalodon vs. Livyatan

is thought to have been approximately the same size as a megalodon, weighing an estimated 100,000 pounds.

©Herschel Hoffmeyer/

While the megalodon was an order of magnitude larger than other sharks in its era, it faced competition from animals like Livyatan.

In today’s oceans, the emergence of killer whales sometimes makes great white sharks flee incredible distances. In one encounter, after killer whales entered a great white hunting ground off California, the shark fled all the way to Hawaii! Like today’s largest sharks, megalodon also faced competition from a giant whale that hunted the same prey. 

Its name was Livyatan, and it was a ferocious competitor to megalodonLivyatan was about the same size as the massive shark, weighing an estimated 100,000 pounds and reaching up to 57 feet in length. In addition, Livyatan had incredibly large teeth that reached over a foot in length, making them the largest known biting teeth of any animal! 

Like megalodon, Livyatan is believed to have died out between 3.6 and 2.6 million years ago. It’s likely the two apex predators both struggled to adapt to climate change and the loss of their primary prey of small-to-medium-size whales. 

Megalodon vs. Great White Shark 

Megalodon Vs. Great White

Megalodon Vs. Great White


Size-wise, the matchup of a megalodon vs. a great white shark is no contest. After all, megalodons were ‘conservatively’ estimated to weigh up to 100,000 pounds while great white sharks rarely grow to more than 5,000 pounds. 

However, when it comes to survival, bigger isn’t always better. Recent research proposes that the much smaller great white shark actually helped cause the megalodon’s extinction!

great white shark

Although much smaller, great white sharks probably contributed to the extinction of the megalodon.

©Alexius Sutandio/

The theory is that around the time when megalodons were struggling to adapt to cooling ocean climates, great white sharks evolved and began competing with juvenile megalodons and hunting smaller whales that were the megalodon’s primary prey. With both megalodon and Livyatan going extinct 2.6 to 3.6 million years ago, great white sharks and killer whales were left as much smaller apex predators of the seas. 

Without the presence of massive predators, whales that filter feed began growing to massive sizes. In fact, this development led to the evolution of the largest animal to ever live on Earth… 

Megalodon vs. Blue Whale 

Blue whales can reach a maximum length of 110 feet and weigh up to 400,000 pounds.

The megalodon and blue whale never met, as the earliest fossils of ‘modern’ blue whales date back to roughly 1.5 million years ago. That’s about a million years after the megalodon is believed to have hunted the oceans. 

When it comes to size, the blue whale dwarfs even the largest megalodon estimates. It’s believed blue whales can reach a maximum length of 110 feet (34 meters) and weigh up to 200 tons (400,000 pounds!). That’s more than twice the size of even the largest megalodon size estimates.

Blue whales and other gigantic whale species have evolved to be so large because there’s no apex predator the size of the megalodon in today’s ocean. Were there a shark of megalodon’s size still alive today, it would surely feast on large whale species such as the blue whale.

With all these matchups being covered, there’s just one question left. Is the blue whale truly the biggest animal ever? 

Are Blue Whales Endangered - A Blue Whale Near the Surface

The blue whale is the largest known animal to live on Earth.

©Andrew Sutton/

The Biggest Animal Ever Is…

Reaching a weight of 400,000 pounds (200 tons), the blue whale is the largest known animal to live on Earth. However, there are many ‘incomplete fossils’ that could point toward creatures that could challenge the blue whale’s title as the biggest animal ever. 

For example, in 2018 paleontologists discovered a 3-foot jaw segment belonging to a newly discovered ichthyosaur. Comparing the jaw segment to more complete ichthyosaur fossils yields an estimate of an animal that could have grown to 85 feet in size and roamed the oceans about 200 million years ago! At that size, the creature could weigh more than any blue whale that’s ever been discovered.

The bottom line: today the blue whale is the largest known animal to have ever lived on the Earth, but in the decades to come, more complete fossil discoveries could rewrite the history books! 

Summary Of The Biggest 5 Giants From The Ocean

RankSea AnimalSize
1Blue Whale400,000 lbs/110 ft long
2Megalodon105,733 lbs-227,510lbs
3Livyatan100,000 lbs/57 ft long
4Mosasaurus56 ft long
5Great White Shark5,000 lbs

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About the Author

Heather Hall is a writer at A-Z Animals, where her primary focus is on plants and animals. Heather has been writing and editing since 2012 and holds a Bachelor of Science in Horticulture. As a resident of the Pacific Northwest, Heather enjoys hiking, gardening, and trail running through the mountains with her dogs.

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