Cynthiacetus is an extinct genus of basilosaurid early whale that lived during the Upper Eocene (Bartonian-Priabonian, 40.4 to 33.9 million years ago.) Specimens has been found in the south-eastern United States, Egypt and Peru.The skull of Cynthiacetus was similar in size and morphology to that of Basilosaurus, but Cynthiacetus lacked the elongated vertebrae of Basilosaurus.