Mosasaurus was a genus of fully-aquatic marine lizards which lived throughout the world’s oceans during the late Cretaceous Period approximately 75-66 million years ago.

Fossils of this animal were first discovered in 1764 within a chalk mine in the town of Maastricht, Netherlands, consisting of three partial jaw fragments; these fossils are currently housed within the Teylers Museum (collection ID code: TM 7424). Later in 1780, a second specimen was found within the same mine consisting of a nearly-complete skull. The fossils were promptly purchased by Dr. Johann L. Hoffmann, a retired army surgeon who had a strong interest in fossils. Later, when the French Republican Army invaded the Netherlands in 1794, the skull was claimed as a trophy of war and was taken to France, where it has resided ever since. The specimen is currently housed within the National Museum of Natural History in Paris, France (collection ID code: MNHN AC 9648).

After its arrival in France, the jaw bones were studied by the famed French scientist and anatomist Prof. Georges Cuvier, who concluded in 1808 that they belonged to a giant marine lizard. However, Cuvier didn’t ascribe a name to these fossils. In 1822, the eminent English geologist William Conybeare officially named it Mosasaurus, “Meuse Lizard”, due to the fossils being found near the Meuse River. In 1829, Gideon Mantell (the same man who named Iguanodon) ascribed it the species name hoffmanni in honor of Dr. Hoffmann.

There are currently five recognized species of Mosasaurus, although there are a handful of others whose validity is debatable:

1. Mosasaurus beaugei – Found in Morocco and Brazil. Dates to the Maastrichtian Stage, 70-66 MYA. Measured 25 feet long.
2. Mosasaurus conodon – Found in Canada and the United States. Dates from the upper Campanian to lower Maastrichtian, 75-68 MYA. Measured 25 feet long.
3. Mosasaurus hoffmanni – Found in the Netherlands, Morrocco, and the United States. Dates to the Maastrichtian Stage, 70-66 MYA. Measured 40 feet long.
4. Mosasaurus lemonnieri – Found in Belgium and the Netherlands. Dates to the Maastrichtian Stage, 70-66 MYA, although some specimens might date slightly earlier to the upper Campanian. Grew to 25 feet long.
5. Mosasaurus missouriensis – Found in Canada and the United States. Dates to the upper Campanian Stage, 75-70 MYA. Measured 25 feet long.

As you can see, most species of Mosasaurus were medium-sized, growing to around 25 feet long. However, Mosasaurus hoffmanni, which is the type species of the genus, seems to have been far larger. Although a complete specimen has never been found, the few bones which have been found were enormous. By comparing these bones to the bones of other mosasaurs that we know more about and making size extrapolations, Mosasaurus hoffmanni is estimated to have measured 40 feet long, the same size as a fully-grown Tyrannosaurus, and some people think it could have gotten even bigger, perhaps 50 feet long. Mosasaurus hoffmanni was also one of the last mosasaurs to have existed before the entire group went extinct at the end of the Cretaceous Period.

Mosasaurus shared its global oceanic habitat with other large mosasaurs. These include the 40 foot long Tylosaurus bernardi (formerly known as Hainosaurus) of Belgium and at least four different species of Prognathodon, one of which (P. saturator) measured up to 30 feet long. It’s not clear how at least three different genera of large carnivorous marine lizards could inhabit the same habitats, but niche partitioning is often given as an explanation, with the idea that the three different genera fed on different prey based upon the shape of their teeth.

Below is a drawing that I made of Mosasaurus hoffmanni. The color pattern is based upon the Australian Perentie Lizard (Varanus giganteus) and the Clown Triggerfish (Balistoides conspicillum).

Mosasaurus hoffmanni. © Jason R. Abdale (September 23, 2024).

I truly enjoy writing my articles and drawing my art, but it’s increasingly clear that I can’t keep this up without your gracious financial assistance. Kindly check out my pages on Redbubble and Fine Art America if you want to purchase merch of my artwork. Consider buying my ancient Roman history books Four Days in September: The Battle of Teutoburg and The Great Illyrian Revolt if you or someone that you know loves that topic. Also, please consider becoming a patron on my Patreon page so that I can afford to purchase the art supplies and research materials that I need to keep posting art and articles onto this website.

Take care, and, as always, keep your pencils sharp.

Categories: Paleontology, Uncategorized

Tags: Africa, art, Cretaceous Period, Europe, Late Cretaceous, lizard, marine, Mesozoic, mosasaur, mosasaurid, Mosasauridae, Mosasaurus, North America, paleo-art, paleontology, Prehistoric, reptile, South America