At a Glance

Attribute	Detail
Scientific name	Mosasaurus hoffmannii
Pronunciation	MOH-za-SORE-us hoff-MAN-ee-eye
Name meaning	“Meuse lizard of Hoffmann” — Latin Mosa (Meuse river) + Greek sauros (lizard)
Classification	Squamata > Mosasauridae > Mosasaurus > M. hoffmannii
Period	Late Cretaceous, 66–70 Ma
Found in	Netherlands, Belgium, Morocco, Russia, North America
Diet	Carnivore — apex marine predator consuming fish, cephalopods, marine birds, and other mosasaurids
Length	~13–14 m (43–46 ft)
Weight	~likely in the range of 14,000–15,000 kg (30,900–33,000 lb)
Status	Extinct

Quick Answer: Mosasaurus facts reveal a massive marine reptile — not a dinosaur — that ruled Late Cretaceous seas roughly 66–70 million years ago. Mosasaurus hoffmannii reached around 13–14 metres (43–46 ft) in length and weighed an estimated likely in the range of 14,000–15,000 kg (30,900–33,000 lb), making it one of the largest predators in its ecosystem. It is classified within Squamata, most closely related to monitor lizards.

The skull of Mosasaurus hoffmannii was first uncovered in a chalk quarry near Maastricht in the 1770s, and that single fossil was enough to help convince the scientific world that extinction was real. This was the specimen Georges Cuvier used to argue that entire species could vanish from the Earth. Today, fossils are known from Europe, Russia, Morocco, and North America. The posts below cover each major aspect of this animal’s biology, history, and ecology in detail.

How Big Was Mosasaurus?

Feature	Detail
Maximum estimated length	~13–14 m (43–46 ft) based on skull extrapolation
Mass estimate	~likely in the range of 14,000–15,000 kg (30,900–33,000 lb), biomechanically modelled
Complete skeletons	Rare — estimates depend on partial material
Jurassic World depiction	~22 m (72 ft) — not supported by fossil evidence

Earlier estimates of 17–18 m (56–59 ft) are not supported by current evidence; the 22 m (72 ft) version seen in the Jurassic World films is a significant exaggeration.

For more details, see our full analysis on Mosasaurus size.

What Did Mosasaurus Eat?

Feature	Detail
Confirmed prey types	Fish, cephalopods, marine birds, other mosasaurids
Evidence type	Gut contents and tooth-marked bones (Tier 1)
Trophic role	Apex predator
Juvenile threat	Cretoxyrhina shark may have preyed on juveniles

For more details, see our full analysis of the Mosasaurus diet.

Mosasaurus vs. Megalodon

Feature	Detail
Temporal overlap	None — approximately 60 Ma separates the two species
Size comparison	Megalodon was larger in both length and mass
Megalodon bite force	Estimated 108,500–182,200 N (biomechanical modelling)
M. hoffmannii bite force	No published biomechanical model exists
Encounter possibility	Zero — any matchup is a thought experiment

For more details, see our full analysis on Mosasaurus vs Megalodon.

Mosasaurus Teeth and Anatomy

Feature	Detail
Tooth type	Conical, recurved, pleurodont
Palatal teeth	Pterygoid (palate) teeth present — secondary gripping row
Jaw feature	Intramandibular joint for prey manipulation
Tooth replacement	Polyphyodont — continuous replacement throughout life
Tail	Hypocercal fluke confirmed by skin impressions

For more details, see our full post on Mosasaurus teeth.

Mosasaurus Discovery and Fossil History

Feature	Detail
Discovery location	St Pietersberg chalk quarries, near Maastricht
Discovery period	1770s
Holotype location	Muséum National d’Histoire Naturelle (MNHN), Paris
Named by	William Conybeare, 1822
Scientific significance	Cuvier used the specimen to establish the concept of extinction

Fossil material is now known from the Netherlands, Belgium, Morocco, Russia, and North America.

For more details, see our full post on Mosasaurus discovery.

Is Mosasaurus a Dinosaur?

Feature	Detail
Classification	Squamata — not Dinosauria
Closest living relatives	Monitor lizards (varanids)
Archosaurian ancestry	Absent
Coexistence with dinosaurs	Same geological period; not the same ecosystems
Phylogenetic placement	Actively debated within varanoid squamates

For more details, see our full post on whether Mosasaurus is a dinosaur.

Mosasaurus Habitat and Range

Feature	Detail
Primary environment	Marine epicontinental seas
Geographic range	Netherlands, Belgium, Morocco, Russia, North America
Terrestrial capability	None — fully aquatic
Freshwater tolerance	Not confirmed for M. hoffmannii
Water conditions	Warm, shallow Late Cretaceous seas

Freshwater mosasaurids do exist — Pannoniasaurus is a confirmed example — but freshwater tolerance has not been demonstrated for M. hoffmannii specifically.

For more details, see our full post on Mosasaurus habitat.

How Fast Was Mosasaurus?

Feature	Detail
Sustained speed estimate	~2 m/s (~7 km/h) — biomechanical modelling
Burst speed	Plausible but not modelled for M. hoffmannii
Locomotion method	Lateral tail undulation
Tail structure	Hypocercal fluke — confirmed by skin impressions

Burst speed claims in popular sources lack a peer-reviewed biomechanical basis for this species specifically.

For more details, see our full post on Mosasaurus speed.

Mosasaurus Behaviour

Feature	Detail
Feeding role	Generalist apex predator — confirmed by fossil evidence
Social behaviour	Unknown — no fossil evidence
Reproductive mode	Viviparity probable — confirmed in related taxa, not directly in M. hoffmannii
Chemosensory detection	Inferred from comparison with varanoid relatives

Speculatively, the leaping behaviour depicted in the Jurassic World films is not supported by any fossil or biomechanical evidence — this is extrapolation, not direct evidence.

For more details, see our full post on Mosasaurus behaviour.

How Do You Pronounce Mosasaurus?

Feature	Detail
Pronunciation	MOH-za-SORE-us
Syllable count	Four — MOH · za · SORE · us
Species epithet	hoffmannii — hoff-MAN-ee-eye
Mosa	Latin for the Meuse river
sauros	Greek for lizard

The name encodes both the place of discovery and the man who found it: the Meuse river runs through Maastricht, and hoffmannii honours fossil collector Johann Leonard Hoffmann.

For more details, see our full post on Mosasaurus pronunciation.

Tylosaurus was a large North American mosasaurid of comparable size that shared Late Cretaceous epicontinental seas, though it is not the same genus as Mosasaurus.
Prognathodon was a heavily built, broad-snouted mosasaurid known from similar formations across Europe and North Africa.
Hainosaurus (sometimes synonymised with Tylosaurus) is another large mosasaurid from the Late Cretaceous of Europe.
Pannoniasaurus is notable as a confirmed freshwater mosasaurid, contrasting with the fully marine habitat of M. hoffmannii.
Platecarpus was a smaller, more lightly built mosasaurid that occupied a different ecological niche within the same Late Cretaceous seas.

Common Questions About Mosasaurus

Was Mosasaurus the biggest marine reptile ever?

Mosasaurus was not definitively the largest marine reptile ever to have lived. At an estimated 13–14 metres (43–46 ft), M. hoffmannii was among the largest mosasaurids, but Jurassic pliosaurs such as Pliosaurus and the ichthyosaur Shonisaurus also reached comparable or greater sizes. Size comparisons across lineages depend on incomplete material and are subject to ongoing revision.

When did Mosasaurus go extinct?

Mosasaurus went extinct at the end of the Cretaceous period, approximately 66 million years ago, during the mass extinction event that also eliminated non-avian dinosaurs. The cause is widely attributed to the Chicxulub asteroid impact and its cascading environmental effects, which collapsed the marine food chains that apex predators like Mosasaurus depended on.

Mosasaurus was related to modern monitor lizards and snakes within the order Squamata. Fossil and molecular evidence places mosasaurids within the varanoid lineage, making the Komodo dragon a distant living cousin — though the exact phylogenetic placement within varanoids remains an active area of research.

Did Mosasaurus live at the same time as T. rex?

Mosasaurus and Tyrannosaurus rex did overlap in geological time, both living during the late Maastrichtian stage of the Late Cretaceous, approximately 66–68 million years ago. They did not, however, share the same environment: T. rex was a terrestrial predator of North American land ecosystems, while Mosasaurus was fully aquatic and inhabited open marine seas.

How do we know what Mosasaurus looked like?

What Mosasaurus looked like is known from fossil skull and skeletal material, supplemented by soft-tissue skin impressions from related mosasaurids. Fossil evidence confirms the general body plan — elongated, paddle-limbed, and tail-finned. The hypocercal tail fluke is supported by skin impression evidence from mosasaurids, though direct attribution to M. hoffmannii specifically carries some uncertainty.

References

Conybeare, W.D. (1822). Additional notices on the fossil genera Ichthyosaurus and Plesiosaurus. Transactions of the Geological Society of London.
Cuvier, G. (1808). Sur le grand animal fossile des carrières de Maastricht. Annales du Muséum national d’Histoire naturelle.
Grigoriev, D.V. (2014). Giant Mosasaurus hoffmannii (Squamata, Mosasauridae) from the Late Cretaceous (Maastrichtian) of Penza, Russia. Proceedings of the Zoological Institute RAS.
Lindgren, J., Caldwell, M.W., Konishi, T., & Chiappe, L.M. (2010). Convergent evolution in aquatic tetrapods: insights from an exceptional fossil mosasaur. PLoS ONE.
Polcyn, M.J., & Bell, G.L. (2005). Russellosaurus coheni n. gen., n. sp., a 92 million-year-old mosasaur from Texas. Netherlands Journal of Geosciences.
Russell, D.A. (1967). Systematics and morphology of American mosasaurs. Bulletin of the Peabody Museum of Natural History.