Yes, mosasaurs are believed to have hunted like killer whales. They lived during the late Cretaceous period and were dominant predators in marine environments. Fossilized remains of mosasaurs have been discovered with evidence of teeth marks on the bones of other marine creatures, suggesting that they engaged in predation. Their morphology, including powerful jaws, long tails for propulsion, and streamlined body shapes, further supports the idea of an active predatory lifestyle.