Mosasaurus Facts for Kids
MOH-zuh-SORE-us · its name means “Meuse lizard”
🌊 Not a dinosaur: a sea reptile that lived at the same time
A giant sea reptile with strong flippers, but not a dinosaur.
- 📏 30 ft9.1 m1 long
- ⚖️ weight: not yet checked
- 🕰️ 65 to 100 million years ago65 to 100 million years ago2
- 🍽️ meat
Mosasaurus was a giant reptile that swam in the sea. It had four flippers and a long tail. It was not a dinosaur.
Mosasaurus lived in the sea at the same time as the last dinosaurs, but it was not one. It was a giant lizard, a cousin of today's snakes and monitor lizards, with a long body, four flippers and a strong tail for swimming. Its big mouth was full of teeth for catching fish and other sea animals, and it came to the surface to breathe air.
Mosasaurus was one of the biggest sea reptiles of the Cretaceous and a top hunter of its seas. Mosasaurs were not dinosaurs: their closest living relatives are snakes and monitor lizards. The first big skull was found in an underground quarry near the Meuse River, long before anyone had a word for dinosaurs. The scientist Georges Cuvier showed it was a giant sea lizard of a kind no longer living, which helped people see that some animals are gone for good.
Every dinosaur number is scientists’ best guess from bones, so each one says where it came from.
How big was Mosasaurus?
Mosasaurus in numbers
| Wingspan | 30 ft9.1 m1a Mosasaurus specimen from Big Bends Boquillas Formation |
|---|---|
| Height at the hips | no checked number yet |
| Weight | no checked number yet |
| When it lived | 65 to 100 million years ago65 to 100 million years ago2mosasaurs in general |
| What it ate | fish, sharks, shelled sea animals called ammonites and other sea animals |
| Fossils found in | the shallow seas that once covered parts of Europe and North America; its first skull was found near the Meuse River, by the city of Maastricht in the Netherlands |
| What kind | a sea reptile: it swam in the sea while dinosaurs walked on land, and was not a dinosaur |
Wow!
- It was a giant sea lizard, not a dinosaur.
- Its closest living cousins are snakes and monitor lizards.
- Its name means Meuse lizard, after the river near where its first skull was found.
🦴 Mosasaurus’s bones
Books about Mosasaurus, free at the library
Ask a grown-up to tap the button: it shows where to borrow a book about Mosasaurus for free.
Where was the land back then?
The continents were in different places when Mosasaurus lived, 65 to 100 million years ago. Open Planet Earth, pick Drifting continents, and slide back in time to see where the land was.
Its neighbours in time
Where these numbers come from
- National Park Service, Big Bend National Park, checked 30 October 2026.
- National Park Service, Fossils and Paleontology, checked 30 October 2026.
- Wikidata, Mosasaurus (Q312131), checked 30 October 2026.
To read more: the Natural History Museum’s Dino Directory (see also, not copied).