Was Any Sea Dinosaur Larger Than a Blue Whale?

The blue whale is the largest animal known to have ever lived, reaching lengths of up to 100 feet and weights of up to 200 tons. But how does it compare to the largest sea dinosaurs? Let’s dive into the depths of history and explore the sizes of these ancient marine reptiles like Mosasaurus, Shonisaurus, and Plesiosaurus.

Mosasaurus vs Blue Whale

The Mosasaurus was one of the most formidable predators of the prehistoric seas. However, when we compare the Mosasaurus to the blue whale, we find that the latter still holds the title for size. The largest Mosasaurus fossils found suggest they reached lengths of about 50-60 feet, roughly half the length of an adult blue whale.

Shonisaurus vs Blue Whale

Another sea dinosaur that often comes up in size comparisons is the Shonisaurus. This ichthyosaur could reach lengths of up to 69 feet, making it one of the largest marine reptiles. Nevertheless, it still falls short when compared to the massive blue whale.

Plesiosaurus vs Mosasaurus

The Plesiosaurus, characterized by its long neck and small head, was another significant marine reptile. However, even the largest Plesiosaurs were not as big as the Mosasaurus, let alone the blue whale. The biggest Plesiosaurus species, such as the Plesiosaurus funkei, are estimated to have been around 40 feet long.

Largest Carnivore Ever in the Ocean

When it comes to the largest carnivore ever in the ocean, the blue whale, despite being a filter feeder, holds this title as well. The blue whale’s diet consists almost exclusively of tiny shrimp-like animals called krill. During feeding season, a single adult blue whale consumes about 4 tons of krill a day.

The Leedsichthys and the Megalodon

The Leedsichthys was a gigantic fish that lived during the Jurassic period. While it wasn’t a dinosaur or marine reptile, it’s worth mentioning due to its size. Some estimates suggest that the Leedsichthys might have reached lengths of up to 50 feet or more. However, even this giant pales in comparison to the blue whale.

Another sea creature often compared to the blue whale is the Megalodon, an extinct species of shark. Although not a dinosaur, the Megalodon was indeed massive, with conservative estimates suggesting a length of around 50 feet, while more speculative ones propose over 60 feet. Despite these impressive dimensions, the blue whale still surpasses the Megalodon in terms of overall size.

Blue Whale Size Comparisons

To put the blue whale’s size into perspective, consider this: a blue whale’s heart is so large that a human could swim through its arteries. Its eyeball alone is bigger than a basketball. Even the largest dinosaurs and marine reptiles cannot compete with such dimensions.

Is There Anything Bigger Than a Blue Whale?

As of now, the blue whale holds the record for the largest creature ever to have existed on Earth. While there are larger structures within living organisms – such as certain fungi’s mycelial networks – no individual animal surpasses the blue whale in size.


While the seas of the Mesozoic era were filled with a variety of large and fearsome marine reptiles, none of them surpassed the blue whale in size. The blue whale remains the largest creature ever to have lived, demonstrating that even after millions of years and countless evolutionary paths, nature has yet to produce a larger animal.

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