Was Any Sea Dinosaur Larger than a Blue Whale?

The Blue whale is the largest animal on land or sea living today. At over 100 feet and up to 400,000 lbs in weight it was truly enormous. Was it the biggest animal to live in the sea? We take a look at some of the sea dinosaur / mosasaur / ichthyosaur competitors for the title of largest sea animal that ever existed below.

Some Scientists have suggested the upper size estimates of the Shastasaurus discovered in 2018 at 26 meters (85 ft) and 120,000 lbs. could challenge the blue whale with an average length of 85 ft and weight of 330,000 lbs. as the largest animal to ever have lived. However, these results are, to date, inconclusive.

In our previous article we discussed if the any Land Based dinosaur was larger than a blue whale. Although close, there is no dinosaur that was larger than a blue whale. There were several that were longer, but nowhere near as heavy.

In this article we take a look at the largest of the sea dinosaurs, fish and sharks that have lived and if any come close to the length and weight of the huge blue whale.

dinosaur facts for kids

As of yet there has been nothing discovered in the fossil record for land or Ocean animals that comes close to the size of a blue whale. However there have been some very large animals discovered, We take a look at 5 of the largest Water dinosaurs (pterosaurs, marine reptiles, fish,sharks and more) and compare them. We have a table for easier comparison below.

What Size is a Blue Whale?

The blue whale is simply massive, there (almost) nothing that can compare to it in sie, even othe rwhales. However even though it is the biggest animal that lives and has ever lived in land or sea it can be hard to understand how big it actually was. We try to give you some comparisons below to make it easier to understand. We have taken this table from our Blue Whale Vs Dinosaurs article here, and added a few things to give you an idea. with a more nautical theme.


AnimalAverage Length (feet)Average Weight (Lbs)Maximum length (feet)Maximum Weight (lbs and tons)Weight in great white sharks
Blue Whale86 Feet long319670 lbs. (145 Tons)111 Feet Long*438, 000 Lbs. (199 tons)110 Great white sharks

*This length may be under question and the official length is 98ft long.

  • A Blue Whale is an long as a 7 cars lined up.
  • That as long as 18 6ft people laying head to toe
  • It would weight about the same as 110 average Great white sharks
  • That’s the same almost 1000 bottlenose dolphins!
  • it had the biggest heart of any animal – bigger than four people.
  • At its average weight The blue whale is the same as the weight of over 200,000 bags of sugar!!

Fast Fact: The only predator known to ris attack a blue whale is the orca, which occasionally works in packs to take down juvenile blue whales. However it is a very risky meal.

The blue whale being the largest ever know animal means it hold quite a few records. We mentioned the heart being the largest of any animal well also the tongue was the larges tof any animal as well.

it used that tongue to push water through its teeth and trap krill between its teeth which have evolved into baleen plates that let water through but stop krill. Krill a small shrimp type animals that the whales eat.

The Blue whale can eat up to 4000 kg of these small shrimp like animals a day which certainly helps it keep up its massive size.

We have a table below to help you compare the largest of different Sea animals ( sharks, Plesiosaurs, ichthyosaurs sharks etc) to the blue whale and get an idea of the differences in size.

Blue Whale Vs Sea dinosaursLength in feetWeight in PoundsWeight Difference to a Blue whaleLength Difference to a Blue whale.
Blue Whale110 ft438000SameSame
Shonisaurus / Shastasaurus85 ft120,000300,000 lbs lighter at top estimatessimilar average, but 10-30ft shorter from top estimates
Mosasaurus57 ft30,000 300,000 lighter than an average blue whale30 feet shorter than average lengths of a blue whale.
Predator X
*Megalodon67 ft230,000 lbs100,000 lbs lighter than a blue whale20 ft shorter than a blue whale.
Leedsichthys50-60 ft90,000 lbs240,000 lighter than an average blue whale25 ft shorter than an average blue whale.

*Megalodon statistics are taken at their absolute maximum estimated size. This is far from proven and we picked it as its kinda cool to imagine a 70 ft long shark swimming in the waters off the coast only 3 million years ago!

Was Shastasaurus larger than a blue whale

Shonisaurus and Shastasaurus: Length and Weight.

The ichthyosaur Shonisaurus has only been discovered in incomplete fossils 37 of them in fact. . These fossils have been found in the Luning Formation of Nevada, USA, This huge marine reptile lived during the late Carnian and late Triassic periods. Makign it as only as the earliest dinsaours aroudn 237-227 million years ago. It is also older than the blue whale by about 236 million years!

There were debatably two species of the Shonisaurus, one was about 50ft long and 30,000 kg called the Shonisaurus poluilis and the other was called the Shastasaurus. This one was a true giant and actually got close, but not close enough from the fossils dicovered so far, to the length of a blue whale.

it could be 69 feet long (21 metres) and weight an estimated 60,000lbs. However, In 2016 there was a jawbone discovered In Somerset England, that has been assigned to Shastasaurus and if scaled up it would give the animal a length of close to 85 feet long!(26 meters) and a weight of 50-60 tons or 120,000lbs this is certainly approaching the length of a blue whale. However, nothing beats the Blue whale for weight, even this massive prehistoric marine reptile .

However if Shastasaurus is correctly scaled up it would put it on the list of the most massive animals to ever live on Earth.

Was Shastasaurus or Shonisaurus bigger than the Blue Whale

Although the 2016 research into the newly discovered jaw bone is inconclusive the shastasaurus and shonisaurus were certainly huge marine reptiles. If accurate their lengths could be 50 ft and 85 feet respectively which puts them similar to an average sized blue whale in length, but the weight of 60-70000 and 120,000 lbs makes them less than half the weight of a blue whale. The blue whale remains the largest Animal on earth!

Predator X: Length and Weight.

In Predator X we have a cool name that somewhat is more impressive than the actual marine reptile. Its scientific name Plesiosaurus Funkei ( also quite cool!) is less commonly used that its media friendly “X Men / Marvel / Comic book name)

it has actually appeared in a few documentaries which has added to the hype of it. However, despite being over esimated it is still an impressive reptile and if the size estimates are accurate it would be the biggest plesiosaur on record.

it is estimated by the natural history museum in Oslo, ( it was found in Norway) to be about 12 meters ( 39 feet long) and by Britannica encyclopedia to be up to 50 feet long. Only britannica have given a weight estimate of 100,000 pounds.

Although smaller than all the other sea creatures on thsi list it was still huge even at the lower sizes.

The brain is thought to be similar to a great white sharks, and thanks to that cool name its reputation is now as well.

Was Predator X larger than a Blue Whale.

Predator X or Plesiosaur Funkei, was certainly the biggest know plesiosaur but it was far from being the largest marine reptile, never mind the largest sea animal and never mind the largest animal to live on Earth. It was 50 ft shorter than a blue whale at its likely length and even if the top weight is close to correct it was still 230,000 lbs lighter than an average blue whale.

megalodon larger than a whale

Megalodon: Length and Weight.

The Megalodon lived in shallow, tropical, and temperate seas, including the Caribbean sea, Bay of Bengal, southern Australia, and eastern Asia around 23 to 3.5 million years ago. It evolved after the large marine reptiles and dinsaours had gone extinct. It went extinct around 3 million years ago due to a likely mixture of climate change and competition form newly evolved whales and sharks that could deal with a wider range of envirnoments.

The Megalodon had teeth as large as human hands, i actually own one that is 6 inches and serrated! and a long fin as tall as an adult human. Researchers In 2021, Victor J. Perez, Ronny M. Leder, and Teddy Badaut used mathematical calculations to calculate the size of the Megalodon and determined that it could have grown “to a total length between 17.4 to 24.2 meters (57 to 79 ft) with a mean of 20.3 meters (67 ft)”

This, if close to being accurate would give the megalodon a potential weight of over 230000 lbs (114 tons) at the 67 ft long size. This is an insanely large shark!

Despite the massive size, Megalodon’s diet would have been large and varied. Megalodon certainly preyed on whales and other large fish. This is supported by the fact that its bite marks have been discovered on whale bones. However it would have also taken dolphins, other sharks and turtles as the opportunity arose.

It was larger than the largest shark swimming today, the whale shark, and certainly more scary!

Was Megalodon bigger than the Blue Whale?

Realistically no Megalodon is not larger in length or weight than a great white shark. Although research vaires on how long they could grow, with the top estimate being 79 ft ( which brings it very close) it was still smaller tan a blue whale. It was likely to be smaller averaging around 50ft. Which is still over two times longer and considerably heaver than a great white shark today.

If it was close to 60 ft plus and bid live today then blue whales would certainly be a potential prey target for them even with their huge size.

Mosasaurus: Size and Weight

Mosasaurus is currently the public eye due to the massively oversized version currently in the Jurassic World series of Movies. They have the :genetic changes” script plot to fall back on but in real life, despite being a huge marine reptiles it certainly wasn’t the blue whale sized animal they have in the movie.

In the Jurassic World movies the mosasaurus is actually larger than a blue whale, or at the least comparable in size to one. Any Mosasaurs reaching this size are simply not in the fossil record.

The largest known mosasaurus was measured at 17 meters long, which would be around 56 feet. At this size mosasaurus would have weighed up to 30,000 lbs. Tthis is still massive but makes it one of the smaller marine reptiles on this page. Certainly smaller than even a small blue whale.

A mosasaur’s body resembled that of a monitor lizard. However, its shape was more streamlined and adapted to swimming. It had long fingers and toe bones, and webbing stretched between their toes provided locomotive power. It was believed that mosasaurs swam much like conger eels, or that they had similar movements to sea snakes.

in recent years this has been changed to them having a more shark like swimming motion with a large powerful tail and stiffer body. We have much more information on Mosasaurus on our page linked here and below.

Was Mosasaurus bigger than a blue whale

Only in hollywood is a mosasaurus larger than a blue whale. The movies Jurassic world doubled the size of the mosasaurus form dramatic license (it worked!!) However even at that size although it would have been longer than a blue whale, it would have still been hundreds of thousands of pounds lighter.

The real mosasaurus was half the length at 57 feet maximum and over 300,000 lbs lighter that even an average blue whale.

The Leedsichthys Fish: Length and Weight

Leedsichthys is an extinct genus of pachycormid fish that lived in the oceans from the Middle to Late Jurassic around 165 to 152 million years ago. Right in the middle of the time of the dinsaours.

They are the largest ray-finned fish known to have existed which means the largest ever fish on Earth. Initially thought to grown to up to 100 feet long this has been scaled down in more recent years to a maximum of 50-60 ft long or around 18-20 meters. This is still absolutely massive for a fish!

At the upper end of their length it is estimated Leedsichthys would have weighed about 45 tons ( 90,000 lbs plus) At that weight it would win any fishing competition if you could land it!

However finding bait night be a problem as like the whale shark it was thought to be a filter feeder eating plankton by filtering sea water. Plankton a tiny tiny animals you are never going to fit on a hook! Probably for the best really!

Was leedsichthys larger than a blue whale.

The Largest fish Leedsichthys may have been, but it was not as big as the largest whale but quite some distance. Even if those earlier estimates of 100 ftt, or even 130 ft were accurate ( and they are thought not to be) it wouldn’t have competed in weight despite still being massive.

At its actually maximum size of 50 to 60 ft in would have approached 100,000 lbs. huge for a fish, but still 230,000 lbs. below an average blue whales weight.


The seas of the Earth have always, it seems, been full of life both great and small. From The hyper large shastasaurus 230 million years ago, to the Megalodon 1 million years ago, till today with the blue whales filing our oceans. However, despite the time of the dinosaurs being commonly thought of as the time of the giants, we can look a little closer to our own time for the true giant. The blue Whale continues to be the largest ever animal to live on Earth, despite challengers getting closer with each discovery!

Don’t forget to check our article on if any Land based dinosaurs could challenge the blue whale as the largest animal to ever live on Earth here and below.







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