The mosasaur was a large marine reptile that lived  during the Late Cretaceous period, approximately  70-66 million years ago. Emerging around the  Campanian age, mosasaurs were apex predators of  their time, dominating the seas. These reptiles were  highly adapted to aquatic life, with streamlined  bodies and powerful tails. Their closest living  relatives are modern-day snakes and monitor lizards.  Fossils have been found worldwide, indicating a  wide distribution. The extinction of mosasaurs  coincided with the mass extinction event that wiped  out the dinosaurs. Their discovery has provided  sis- fficant insights into the evolution of marine  reptiles.