Dinosaur Encyclopedia · Pack 3
Mosasaurus
MOH-za-SORE-us
For younger explorers (ages 4–7)
Mosasaurus facts for kids
01
Mosasaurus had TWO rows of teeth — extra teeth on the roof of its mouth!
02
It was related to Komodo dragons and monitor lizards, not dinosaurs.
03
Mosasaurus was so big it could swallow a shark.
For older explorers (ages 8–12)
Advanced Mosasaurus science
The discovery of Mosasaurus in the 1760s was one of the first pieces of evidence that extinction — the permanent disappearance of a species — was real.
Mosasaurus's jaws could unhinge slightly, like a snake's, allowing it to swallow prey much larger than its head.
Mosasaurs evolved from land-dwelling lizards that returned to the sea — their legs became flippers in less than 20 million years.
Latest science
Mosasaurus: The Sea Monster That Helped Invent Paleontology
In 1764, workers quarrying limestone near Maastricht in the Netherlands discovered an enormous fossilized skull. For decades, scientists argued about what it was — some said a whale, others a crocodile. It wasn't until 1822 that William Conybeare formally recognized it as a giant extinct lizard and named it Mosasaurus ('Meuse lizard,' after the river near where it was found).
That skull made history not just for what it was, but for when it was found: it was one of the first giant prehistoric creatures to force scientists into a startling conclusion — creatures had gone extinct. Before Mosasaurus, most European scholars assumed God had created all living things and none had disappeared. The giant Maastricht skull forced a confrontation with extinction as a fact of nature.
Today we know Mosasaurus hoffmannii reached up to 13 meters and dominated the Late Cretaceous seas. It hunted with two rows of teeth and jaws that could partially disarticulate, snake-like, to engulf large prey. When the Cretaceous ended 66 million years ago, Mosasaurus went with it.
Journal Citation
Polcyn, M.J. et al. (2014). Physical drivers of mosasaur evolution. Palaeogeography, Palaeoclimatology, Palaeoecology, 400, 17–27.
Cretaceous neighbors
Who lived alongside Mosasaurus?
Elasmosaurus
carnivoreA plesiosaur with a neck so long it made up half its body — a different kind of sea reptile, NOT a dinosaur either.
Ammonite
carnivoreA spiral-shelled creature like a modern nautilus — crushed flat in Mosasaurus's jaws. Billions lived in the Cretaceous seas.
Pteranodon
carnivoreA flying reptile with a huge wingspan that soared above the same seas, snatching fish from the surface.
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