Ectenosaurus is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Plioplatecarpinae subfamily alongside genera like Angolasaurus and Platecarpus. Ectenosaurus is known from the Santonian and Campanian of Kansas, Alabama, and Texas. The generic name means "Drawn-out lizard", from Greek ectenes ("drawn-out") and Greek sauros ("lizard") referencing the elongated muzzle.