''Thalassoleon'' ("sea lion" ) is an extinct genus of large

fur seal Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than Earless seal, true seals, and share with them external ears (Pinna (anatomy ...

. ''Thalassoleon'' inhabited the Northern Pacific Ocean in latest Miocene and early Pliocene. Fossils of ''T. mexicanus'' are known from

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

and southern California. ''T. macnallyae'' is known from central California, and ''T. inouei'' (which may be a synonym of ''T. macnallyae'') is known from

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. ''Thalassoleon'' could be the ancestor of the modern

northern fur seal The northern fur seal (''Callorhinus ursinus'') is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the ...

''T. mexicanus'' was comparable in size to the largest modern fur seals, with an old-male skull length of 272 mm and an estimated minimal weight of 295–318 kg (650–700 lb). Holotype of ''T. macnallyae'', UCMP 112809, is a male equal in size to ''T. mexicanus''.

References

Miocene pinnipeds Miocene mammals of North America Miocene mammals of Asia Prehistoric pinnipeds of North America Fossil taxa described in 1977 Prehistoric carnivoran genera Otariinae {{paleo-carnivora-stub