The Mosasaurus was a large aquatic lizard and part of the group of marine reptiles called mosasaurs. These were a group of large marine reptiles and were the dominant marine predators for millions of years up until the end of the Cretaceous period. The Mosasaurus was one of the largest mosasaurs known and scientists continue to argue if it’s closest living relatives are snakes or lizards.

Mosasaurus were aquatic reptiles, meaning even though they lived most of the time in the water, they still came up to the surface and breathed air. Similar to modern day aquatic reptiles such as crocodiles or sea turtles.

They were said to have flippers rather than feet that made it more difficult for them on land and meant they probably spend little time there.

Mosasaurus swimming

Image source: Jurassic world universe 

About mosasaurus

The name Mosasaurus comes from the term “Meuse” which is the European river a fossil was first found, and “Lizard”. The first fossil was discovered in 1764 and was known to have roamed the waters of the earth 82 to 62 million years ago.

There have been over 40 known species identified so far and most have been found in North America although there have been many findings in South America, Europe, Africa, Asia, and even Antarctica.

Quick Mosasaurus Facts

First Found: Europe by Dr James Parkinson
When it lived: Cretaceous period, 82 – 62 Million years ago
Weight: Up to 28 tonnes
Length Up to 58ft / 17.6 meters
Diet: Carnivore, meat

mosasaurus Habitat

As Mosasaurus was an aquatic reptile it was living in the warm and shallow seas of its time, it needed air to be able to breath and with its efficient body that could glide in the water, it was a powerful swimmer. Scientists have said that the Mosasaurus would give birth at sea and would not go to the shore to lay eggs. This may have been an effective way of reproducing knowing what dinosaurs were roaming the earth at that time who would have ate the eggs.

How big was mosasaurus?

As previously mentioned full fossils of Mosasaurus have not been discovered so Scientists have had to make well hypothesised predictions and the largest that we know of was possibly 17.6 meters (58 feet).

How big was Mosasaurus?

Slate Weasel, CC0, via Wikimedia Commons


The first fossils of Mosasaurus were discovered in a chalk quarry in the Netherlands in 1764. A better skull fossil was found at the same location roughly 14 years later and an amateur geologist took keen interest in this although he did not make the discovery directly.

It was initially thought that these discoveries were crocodiles only to be disputed years later. These fossils were given the temporary name of “Mosasaurus” by an English Doctor James Parkinson in 1822 on the advice of William Dean Conybeare and this name was never changed.

Mosasaurs skeleton

Ghedoghedo, CC BY-SA 3.0, via Wikimedia Commons

There are several species of Mosasaurus that have been discovered and named from 1834 to 1952, including Mosasaurus conodon that was named by Edward Cope, an American palaeontologist in 1881. The latest and fifth species Mosasaurus beaugei, was named by French palaeontologist Camille Arambourg in 1952.


Mosasaurus was a top predator of the seas at the time and fed on whatever it could catch and eat such as sea turtles, squid, sharks, bony fish, birds, and cephalopods. Its likely the Mosasaurus hunted in open waters near the surfaces.

Mosasaurus may have also occasionally ate each other some scientists have speculated, as a result of their aggression. Fossils have shown that some have had injuries and scientists concluded this was from combat at a pre adult age possibly from inter species fighting.


Mosasaurus’s size has largely been estimated and the longest is said to have been 17.6 meters (58 feet). Estimations have been widely completed by studying the Mosasaurus skull, as incomplete fossils have not allowed precise calculations.

Its weight has also been estimated to be around 28 tons which if we compare to the modern-day Blue Whale, it was still some way off this as Blue Whales can weigh up to 150 tons.

How heavy was Mosasaurus?

Nobu Tamura email:nobu.tamura@yahoo.com, CC BY-SA 4.0, via Wikimedia Commons


The teeth lined their powerful jaws which were able to extend the lower jaw sideways as well as downwards which helped them whilst feeding on particularly large prey. New teeth were continually growing until they pushed through the old teeth and forced them to shed.

It meant they had an efficient system as like many carnivores their teeth were essential in catching their prey. Scientists have estimated that this whole process from start to finish took approximately just over two years.

Mosasaurus hoffmanni first specimen teeth


The Mosasaurus had a powerful tail and a streamlined body which is what was expected and needed for a powerful reptile to survive in the water.

Similar dinosaurs to MOSASAURUS


Tylosaurus was known as the most fierce and dangerous hunter of the seas 90 to 86 million years ago during the Cretaceous period. Tylosaurus was a carnivore and ate whatever was in its path, and evidence of its prey has been identified through fossilised stomach contents which have included fish bones, birds, plesiosaurs, other mosasaurs, and sharks.

It was known as apex predator which is similar to the modern day great white shark, meaning it was one of the top predators of its time. Its teeth were cone shaped and used its snout to locate its prey.

When it opened its powerful jaws fully, two extra rows of teeth appeared which allowed the Tylosaurus to fully consumed its meal and once the Tylosaurus got hold of its prey there was little chance of escape.

They were probably not the fastest swimmers but when you are an apex predator it probably didn’t need to be. Scientists have said Tylosaurus probably approached its prey from below, as well as being, unsighted it stayed under the radar of other sensory adaptions. The secent of a preditor would also drift sideways and not upwards due to the sea currents. A predatorial tactic used my modern Tylosaurus equivalents. 

Tylosaurus fossils have been discovered in Kansas, United States and the largest estimation from fossil remains of a Tylosaurus is 12 to 15.8 meters (39 to 52 feet) in length. There have been estimates from leading palaeontologists that its length could have got to 20 meters (66 feet) but with not actual evidence to back this up it will remain a theory.

The Tylosaurus was made famous in the film “Jurassic Park: The Game” and has been referred to as the “T-rex of the seas”.


Part of the mosasaur family, the Platecarpus, lived around 84 to 81 million years ago which was during the late Cretaceous period. Platecarpus was a medium sized mosasaur and its fossils have been discovered in the United States, Belgium, and African ancient sea beds.

Platecarpus grew up to 4.3m (14 feet) in length, they had many iconic mosasaur features such as a long muscular body, flipper like limbs, and jaws that were lined with cone shaped teeth which were less robust than other mosasaurs.

This enabled the Platecarpus to hunt in shallow waters for its diet of small fish and squid, although with its thickened ear drums some scientists have said it could chase fish and dive into deeper waters if needed. Its tail was half the length of its body and was downward facing which may indicate it was a fast swimmer.


Dmitry Bogdanov, CC BY 3.0, via Wikimedia Commons

Summary of mosasaurus

  • The very first Mosasaurus fossils were discovered in 1764 and then named in 1822 by English Dr James Parkinson.
  • Mosasaurus fossils have been found in North America, South America, Europe, Africa, Asia, and even Antarctica.
  • Mosasaurus was an aquatic reptile that breathed air.
  • Mosasaurus was a mosasaurs which means marine reptiles.
  • Mosasaurus lived 82 to 62 million years ago in the Cretaceous period. 
  • Mosasaurus was estimated to measure up to 17.6 meters (58 feet) in length
  • Mosasaurus ate sea turtles, squid, sharks, bony fish, birds, and cephalopods

Further Reading & Study

Last Updated on 02/06/2021 by