How big was Mosasaurus?

Probably the most famous of all the prehistoric marine reptiles that lived at the same time as the dinosaurs is the Mosasaurus. In no small part thanks to its appearance in the movie Jurassic World. in that it was a blue whale sized monster with a taste for great white sharks. Now while the Mosasaurus was certainly huge, we take a look at just how big it was in this how big was a Mosasaurus article.

Mosasaurus is estimates to have measured from 13 to 17 metres in length (43-58 feet) and have weighed at the lower estimates 6-8000 kg (13-18,000 lbs.) However at the upper length estimates it would have exceeded this by some measure and may have weighed upwards of 15000 kg (30-40,000 lbs. )

there have always been huge animals living in earths oceans, and Mosasaurus was no exception. This giant marine predator belonged to the mosasaur family and lived during the Late Cretaceous period from about 80 to 66 million years ago. Although not the largest marine reptile, that title likely goes to the Sahstasaurus, the Mosasaurus was undeniably a huge reptile and we explore this below.


Note: Mosasaurus in Meg 2: The trench

We have one of our feelings that in the megalodon movie “The Meg 2: The Trench” they might slip in a Mosasaurus or three. In the book it is kronosaurus, but with Mosasaurus being more popular and actually bigger if not heavier, we have one of those feelings we get around Hollywood movies when they are dealing with dinosaurs. . ( we are not right all the time though)

A couple of the Quotes from Jurassic world seem to fit here, and i am not even sure of they realize the irony of them.

“Corporate felt we need to up the wow factor,

they’re Dinosaurs, WOW enough!”

Owen grady and Claire Deering


“Bigger”, “Scarier”… “Cooler” I believe is the word that you used in your memo. You cannot have an animal with exaggerated predator features without the corresponding behavioral traits.”

Henry Wu

Either way, prehistoric marine life has had no where near the exposure in the media that their dinosaur cousins have had so any movie that has them in will be a welcome change!

What Was the Mosasaurus?

Mosasaurus was a carnivorous marine reptile that lived approximately 83 to 66 million years ago during the Late Cretaceous period. Its fossils have been found across the globe, from North America to Europe and Africa, suggesting a wide distribution in the ancient seas.

it name means ‘lizard of the Meuse River” named after where it was was discovered in 1764, but the name wasn’t given until 1829 with further species being names in , 1834, 1881, 1889 and 1952.

Like the Kronosaurus, which we discuss here on the site, Mosasaurus was a four-flippered predator with a large head, powerful jaws, and sharp teeth.

However, Mosasaurus had a more elongated body and a longer tail, which likely made it a faster and more agile swimmer. Its diet consisted of fish, turtles, squids, and other marine reptiles, including smaller mosasaurs.

We have a facts page and downloads about the Mosasaurus here on the site you can try the link and the image below.

How Big Was Mosasaurus?

Mosasaurus, as we stated above, was a huge marine reptile It has an estimated length of 13 to 18 meters (43 to 59 feet) and a weight of around 5,000 to 8,000 kg (11,000 to 17,600 lbs.). This makes is huge, just not Jurassic World Huge!. Regardless of the exact size, it was one of the largest marine reptiles of its time, or any other time for that matter.

Marine ReptileLengthWeightWhen it lived
Mosasaurus13-18 metres (43-59 feet) 5-8000 kg ( 11-17600 lbs.)70-66 million years ago

Length of Mosasaurus

While all the known species of Mosasaurus were long, it is Mosasaurs Hoffmannii that is thought to have been the longest. Initial estimates of its length were around 17 to 18 metres – 55-59 feet long. Or about as long as a Megalodon.

However later estimates have suggested a lower average size at least, or around 13 metres, or 43 feet. it was still one of the largest marine reptiles of the Late Cretaceous period and even the smaller species like Mosasaurus missouriensis would have topped 25 feet in length.

Weight of Mosasaurus

The weight of Mosasaurus is estimated to be between 5,000 to 8,000 kg (11,000 to 17,600 lbs.). however this is the estimate for the 30 plus feet Mosasaurus. if it was indeed up to 50 feet plus in length then it would have weighed upwards of 15,000 kg ( 36000 lbs.) and if that length probably considerably more.

This massive weight contributed to its power and strength as a marine predator. With such a heavy body, Mosasaurus would have been able to take on large and powerful prey items, including other sizable marine reptiles.

Comparison with Other Marine Reptiles

To better understand the size of Mosasaurus, let’s compare it to other prehistoric marine reptiles that have been discovered. As you will see Mosasaurus was not the largest of the Marine reptiles but was still a very impressive size.

Marine ReptileLength (m/f)Weight (kg/lbs)When it Lived (mya)
Mosasaurus17-18 meters (56-59 feet) ( more likely 13 metres – 43 feet)5,000-8,000 kg (11,000-17,600 lbs)83 – 66 mya
Kronosaurus9-10.5 meters (30-34 feet)10,000-13,000 kg (22,000-30,865 lbs)125-99 mya
Plesiosaurus4-4.5 meters (13-15 feet)450 kg (990 lbs)200-175 mya
Ichthyosaurus2-3.3 meters (6.5-11 feet)90-220 kg (200-490 lbs)250-90 mya
Liopleurodon6-7 meters (20-23 feet) up to 10 metres1,500-1,750 kg (3,300-3,850 lbs) up to 8000 lbs166-155 mya
Elasmosaurus10 – 13 meters (33 – 46 feet)2,000 kg (4,400 lbs)80 mya
Sahstasaurus21 metres (69 feet)81,000 kg ( 178,574 lbs235 – 205 mya


How Do We Know the Size of Mosasaurus?

As with other prehistoric creatures, scientists and paleontologists use various methods to estimate the size of marine reptiles like Mosasaurus. The size of Mosasaurus is based on the analysis of fossil specimens that have been discovered and studied by paleontologists.

By examining the fossilized bones, scientists can reconstruct the skeleton and estimate the overall size and dimensions of the marine reptile. Comparing Mosasaurus with other marine reptiles and using computer models can also help work out their size.

Size Comparisons with Modern-Day Animals

To give you some idea of how large Mosasaurus actually was, we have compared it to some more common animals you might see today, though hopefully from a long distance away! While there are bigger animals in the sea you can see today none of them are quite as predatory as the mosasaurs were.

We do have sperm whales, and killer whales ( although they are likely smaller) however, being mammals and more intelligent, they would do not see humans as a food source.

If a mosasaurus were living today, or a kronosaurus or anything similar then we would certainly be a snack sized treat which we are sure the Meg 2: The Trench movie is going to make full use of whether it goes the Kronosaurus or the Mosasaurus route.

Table 2: Mosasaurus size comparison modern day Marine animals.

Marine ReptileLength (m/f)Weight (kg/lbs)
Mosasaurus17-18 meters (56-59 feet) ( more likely 13 metres – 43 feet)5,000-8,000 kg (11,000-17,600 lbs) More if up to 58 feet.
Blue Whale24-30 meters (79-98 feet)130,000-153,000 kg (250,000-300,000 lbs)
Orca (Killer Whale)7-9 meters (23-30 feet)5,400 kg (11,905 lbs)
Great White Shark6 meters (20 feet)2,000 kg (4,409 lbs)
Salt Water Crocodile7 m (23 feet)2,000 kg (4,400 lb)

Are Megalodon Alive Today?

Who would win in a fight between Mosasaurus and Megalodon?

We will have a larger article on this in due course but for the moment here are our thoughts.

There is a fascination with hypothetical battles between prehistoric creatures, and the matchup between Mosasaurus and Megalodon is no exception.

Although they never actually coexisted, with Mosasaurus living during the Late Cretaceous period and Megalodon emerging much later during the Miocene epoch, we can still speculate on the outcome of a battle between these two colossal marine predators and in reality it would be pretty one sided.

As mentioned earlier,

  • Mosasaurus measured between 13-18 meters in length (43-59 feet) and weighed between 5,000-8,000 kg (11,000-17,600 lbs).
  • In contrast, the Megalodon was substantially larger, with estimates ranging from 15 to 18 meters (for females) (50 to 60 feet) in length and weighing around 50,000 to 60,000 kg (110,000 to 132,000 lbs).

Megalodon’s massive size and powerful bite force would definitely give it a significant advantage in a one-on-one confrontation, making it the victor. However, Mosasaurus was an agile predator with strong jaws and sharp teeth, which would have allowed it to put up a fierce if unsuccessful fight.

Also the Megalodon had evolved to attack prey larger than itself, and the mosasaurus to tackle prey smaller. not only would the fight be one sided, the megalodon would actually consider a Mosasaurus to be nothing more than prey.

We have a selection of articles on Megalodon and other of the large Marine reptiles here on the site you can check them out in the list below.


So while Mosasaurus at its upper estimates may have been over 15,000 kg and 18 metres (58 feet) long, it still is smaller than some animals that live in our oceans today. though with the exception of the Sperm whale it is still one of the biggest toothed animals of all time.

While it may have been blue whale sized in Jurassic World, they really didn’t have to make it such an exaggerated size. It certainly didn’t need to be bigger, scarier or cooler with more teeth. it was all those things when it was a regular size!

We have a series of articles on How Big Dinosaurs were, including sauropods and carnivores, and you can follow the links below to check out the size of other popular dinosaurs. We are expanding this section on a regular basis.

How Big was AllosaurusHow Big was T-RexHow Big was PterodactylHow Big was Triceratops
How Big was StegosaurusHow Big was AmphicoeliasHow Big were Dinosaur BabiesHow big was Spinosaurus
How Big were dinosaur eggsHow Big was a ParasaurolophusHow Big was CarnotaurusHow Big Was Giganotosaurus
How big was DilophosaurusHow Big was ArgentinosaurusHow big was VelociraptorHow big was Brachiosaurus
How Big was AnkylosaurusHow big was CarcharodontosaurusHow big was therizinosaurusHow big was Ceratosaurus
How big was KronosaurusHow big was Meraxes gigasHow big was MosasaurusHow big was Megalodon


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