The evolution and occurrence of fossil sea turtles at the Pacific margin of South Americais poorly known and restricted to Neogene (Miocene/Pliocene) findings from thePisco Formation, Peru. Here we report and describe the first record of Oligocene(late Oligocene, ∼24 Ma) Pan-Cheloniidae sea turtle remains of South America. Thefossil material corresponds to a single, isolated and well-preserved costal bone found atthe Montañita/Olón locality, Santa Elena Province, Ecuador. Comparisons with otherOligocene and extant representatives allow us to confirm that belongs to a sea turtlecharacterized by: lack of lateral ossification, allowing the dorsal exposure of the distalend of ribs; dorsal surface of bone sculptured, changing from dense vermiculation atthe vertebral scute region to anastomosing pattern of grooves at the most lateral portionof the costal. This fossil finding shows the high potential that the Ecuadorian Oligoceneoutcrops have in order to explore the evolution and paleobiogeography distribution ofsea turtles by the time that the Pacific and the Atlantic oceans were connected via thePanama basin.