72–66 million years old

Mosasaurus, also known as the Maas lizard, is a group of extinct dinosaurs that lived in the sea. The Mosasaurus is one of the few dinosaurs that was discovered in the Netherlands namely in the Sint Pietersberg, Limburg. Nevertheless, it is not named after the mountain, but after the river that flows at the foot of the mountain: the Meuse. This river is called mosaics in Latin. The Mosasaurus lived in the Maastrichtien, the last part of the Cretaceous, about 71.3 to 65.4 million years ago. As you may notice, the name Maastrichtien looks like Maastricht and indeed, this period is named after the city of Maastricht.