Mosasaurs

Mosasaurs (from Latin Mosa meaning the 'Meuse river' in the Netherlands, and Greek sauros meaning 'lizard') were serpentine marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse about 1780. These ferocious marine predators are now considered to be the closest relatives of snakes, due to cladistic analysis of symptomatic similarities in jaw and skull anatomies.Mosasaurs were not dinosaurs but lepidosaurs, reptiles with overlapping scales.

These predators evolved from semi-aquatic squamates known as the aigialosaurs, close relatives of modern-day monitor lizards, in the Early Cretaceous Period. During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators.