desmostylian

Of or pertaining to the Desmostylia, an extinct order of marine mammals.

Any member of the Desmostylia.

Herbivores have been the largest bottom-dwelling marine animals since at least the Late Oligocene, with the evolution of desmostylians and the Early Pliocene replacement by large sirenians, and perhaps since the Late Cretaceous if some sea turtles were herbivorous at that time.