Oligocene genus first appearances

thumb|Skull of P. ferox Peltephilus, the horned armadillo, is an extinct genus of armadillo xenarthran mammals that first inhabited Argentina during the Oligocene epoch, and became extinct in the Miocene epoch. Notably, the scutes on its head were so developed that they formed horns. Aside from the horned gophers of North America, it is the only known fossorial horned mammal.

Stenomylus is an extinct genus of miniature camelid native to North America that is known from the Oligocene and Miocene epochs(23.1~16.3Ma). Its name is derived from the Greek (, "narrow") and (, "molar").

Yarala is a genus of fossil mammals that resemble contemporary bandicoots. The superfamily Yaraloidea and family Yaralidae were created following the discovery of the type species Yarala burchfieldi in 1995, on the basis that it lacks synapomorphies that unite all other peramelemorphian taxa.

Merycochoerus (Greek: "ruminant" (merux)-like "swine" (khoiros)) is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. They lived during the Early Oligocene 33.9—30.8 mya, existing for approximately . Fossils are widespread through the western United States.

Amphechinus is an extinct genus of hedgehog of the family Erinaceidae, which lived in Asia and Europe during the Oligocene and in North America, Africa, Asia and Europe during the Miocene. The genus contains at least 14 species. It is classified in the subfamily Erinaceinae and in the family Erinaceidae.

Hanleya is a genus of polyplacophoran molluscs known from Oligocene and Miocene fossils; it is represented today by a number of species including H. sinica Xu 1990 (China), H. brachyplax (Brazil) and H. hanleyi Bean in Thorpe, 1844 (Chile), which feeds on sponges.

Temnocyon is an extinct genus of amphicyonids endemic to North America. It lived from the Oligocene to Early Miocene approximately 30.8—20.4 mya, existing for about .

Arktocara is an extinct genus of river dolphin from the Oligocene epoch of Alaska, containing one species, A. yakataga. Having been discovered in 25-million-year-old strata near the 60th parallel north, it is perhaps the oldest-known crown toothed whale and the northmost river dolphin discovered. It was a member of the now-extinct family Allodelphinidae, along with the genera Allodelphis, Goedertius, Ninjadelphis, and Zarhinocetus. It measured approximately , comparable to its closest living relative, the South Asian river dolphin, which measures . However, the animal probably had an elongated

Mammacyon is an extinct genus of medium-sized amphicyonids endemic to North America during the Late Oligocene and Early Miocene. It lived from 26.3 to 20.4 Ma, existing for approximately .

Rhyssoplax is a genus of chitons in the family Chitonidae, endemic to Australia, New Zealand, New Caledonia, Norfolk Island, and the Kermadec Islands.

Psephophorus is an extinct genus of sea turtle that lived from the Oligocene to the Pliocene. Its remains have been found in Europe, Africa, North America, and New Zealand. It was first named by Hermann von Meyer in 1847, and contains eight species, P. polygonus, P. calvertensis, P. eocaenus, P. oregonesis, P. californiensis, P. rupeliensis, P. scaldii, and P. terrypratchetti.