Mosasaurus Hoffmannii, commonly known as Mosasaurus, is an extinct species of amphibious reptiles that adapted well to the ocean environment and were widespread throughout the Cretaceous Period, approximately 145 million to 66 million years ago. For food access, the Mosasaurs clashed with several marine reptiles like the Ichthyosaurs and Plesiosaurs.

The name Mosasaurus is an homage to its initial discovery of fossilized sites close to the Meuse River. Researchers remain split over the specific connections of Mosasaurus about whether monitor lizards or serpents are indeed the nearest extant descendants.

Featured Image Credit: Herman Pijpers


Mosasaurs were reptile-like creatures with elongated snouts and massive skulls. Its appendages were changed into flippers with fewer digits and toe bones and smaller leg bone fragments than their forebears. Its body’s rear portion was lengthy, with a little down curve at the tip, which resembled the initial Ichthyosaurs. 

Mosasaurs was a reptile-like creature with an elongated skull
Mosasaurs was a reptile-like creature with an elongated skull

Credit: Tim Evanson

The cranium of Mosasaurs, which also are linked to current monitor lizards, had a nearly identical anatomy that’s found in contemporary monitor lizards. The jaws had several cylindrical, moderately recurved fangs that were each fixed in a separate receptacle. The jawbones stand out because they had a mid-length connection that was only joined at the front by tendons.


Mosasaurus was indeed an apex predator that lived in the waters and was definitely a carnivore. Most certainly encroached on a variety of fish, shark species, cephalopods, seabirds, as well as other oceanic reptiles like turtles, with some evidence pointing to cabalistic behaviors towards other Mosasaurs. According to researchers, its dietary choices would have consisted of almost any species. Considering its anatomy, it’s thought that they would distinctly prefer to hunt in open waters, close to the shoreline, or in relatively shallow depths where agility makes all the difference.


Mosasaurus lived in a significant area of the North Atlantic and its nearby sea routes, according to archaeological data. These species’ remains have been discovered in numerous places, including North America alongside Latin America, Africa, Europe, Asia, and even Antarctica. 

Mosasaurs remains have been discovered across the seven continents
Mosasaurs remains have been discovered across the seven continents

Credit: Peter Miller

This implies that its native environment includes a variety of climatic settings, such as tropics and subtropics, arctic, and milder climate conditions. Such habitat adaptations are a result of prey availability. Their ability to survive and thrive was partly thanks to their vast choice of food but also to withstand taxing environments.


Like the majority of contemporary mammals, Mosasaurus was probably viviparous, producing live young specimens. Although live birth has not been proven to have occurred in Mosasaurus, it has been documented in various other Mosasaurs species. The likelihood of viviparity in 

Mosasaurus is shown by the complete lack of any proof supporting exogenous egg-based fertilization. Because Mosasaurus were gregarious, their juveniles could be raised in open water without the need for nurseries because they were generally proficient swimmers early in life. All in all, there is still debate on the specifics of Mosasaurus reproduction due to the numerous specimens.


Mosasaurus were apex predators, meaning that they had no direct predators. Nonetheless, Mosasaurus coexisted with other sizable carnivorous Mosasaurs that were also regarded as apex predators, the most notable of which were the Tylosaurines and Prognathodon. There are documented cases of interspecies cannibalism, and other bigger predators might have attacked them but the latter is not confirmed.

Mosasaurs went extinct due to the changing environment at the time
Mosasaurs went extinct due to the changing environment at the time

Credit: Herman PijpersTim Evanson

The world’s oceans declined in the late Maastrichtian period depriving the regions of their nutritional sea lanes, changing flow and nutrition dynamics, and decreasing the number of sites that could support Mosasaurus. By gaining access to new environments in much more open seas, the genus evolved.

Facts about the Mosasaurus

  1. Mosasaurus went extinct around 63 million years ago.
  2. Mosasaurus thrived for about 19-20 million years.
  3. Approximately 40-50 razor-sharp, conical canines are present in Mosasaurus.
  4. Mosasaurus were between 35-60 ft in length.
  5. The smallest Mosasaurus size was only 3 ft in length.


What killed the Mosasaurus?

Mosasaurs and other non-avian creatures vanished from the archaeological record approximately 65.5 million years ago following a massive asteroid impact at the end of the Cretaceous epoch, leading to the extinction of nearly 90% of creatures on earth.

Is a Megalodon bigger than a Mosasaurus?

The majority of Mosasaurs couldn’t compete with Megalodons in dimensions. However, the longest specimens of Mosasaurus have length estimations that are in line with Megalodon’s length projection of 60 ft; thus, at least their lengths are comparable.

When was the first Mosasaurus fossil discovered?

The oldest recorded remains of Mosasaurus were discovered as heads in limestone quarries not far from the Dutch city of Maastricht in the mid-to-late 18th century. At first, these craniums were mistaken for croc or whalebone fragments. The scientific name Mosasaurus was given to it by William Daniel Conybeare in 1822 in connection to its discovery in geological sites close to the Meuse River.

How many species of Mosasaurus are there?

Mosasaurus Hoffmannii is the most prevalent of the species, followed by currently recognized species such as the M. missouriensis Harlan, M. conodon Cope, M. lemonnier Dollo, and M. beaugei Arambourg. However, that’s not to say that the list is complete because the following species are being reconsidered if they truly fulfill the requirements to be designated Masasaurus. The following are being reconsidered: M. mokoroa, M. hobetsuensis, M. flemingi Wiffen, M. prismaticos.

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