Oligocene sirenians

Metaxytherium is an extinct genus of dugong that lived from the Oligocene until the end of the Pliocene. Fossil remains have been found in Africa, Europe, North America and South America. Generally marine seagrass specialists, they inhabited the warm and shallow waters of the Paratethys, Mediterranean, Caribbean Sea and Pacific coastline. American species of Metaxytherium are considered to be ancestral to the North Pacific family Hydrodamalinae, which includes the giant Steller's sea cow.

Halitherium is a dubious genus of extinct dugongid sea cow that arose in the late Eocene, then became extinct during the early Oligocene. Its fossils are common in European shales. Inside its flippers were finger bones that did not stick out. Halitherium also had the remnants of back legs, which did not show externally. However, it did have a basic femur, joined to a reduced pelvis. Halitherium also had elongated ribs, presumably to increase lung capacity to provide fine control of buoyancy.

left|thumb|Drawing of skeleton. left|thumb|E. libyca and an extant manatee by Charles R. Knight, 1907 left|thumb|Size of Eosiren (purple) compared to other Eocene sirenians and a human. Eosiren is an extinct genus of sea cow that lived during the Late Eocene (later Priabonian) to Early Oligocene (Rupelian). Several fossils have been found in Egypt. It seems like the species E. abeli were contemporaneous with Protosiren and Eotheroides. Like them, Eosiren closely resembled modern sirenians, with the primary differences being somewhat larger innominates and the presence of thigh bones.

Anomotherium is an extinct genus of manatee that lived in the shallow seas of what is now Northern Germany. Its closest relative is Miosiren. Fossils of the genus have been found in the Bohlen and Doberg Formations of Germany.

Caribosiren is an extinct genus of afrotherian mammal which existed in what is now Puerto Rico during the Chattian stage of the Oligocene epoch. Fossils have been recovered from the San Sebastián Limestone.