A cast of a Monotherium skeleton
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Suborder: Pinnipedia
Family: Phocidae
Subfamily: Monachinae
Genus: Monotherium
van Beneden, 1876
Type species
Monotherium delognii
van Beneden, 1876
Referred species
  • Monotherium aberratum (van Beneden, 1876)
  • Monotherium affine (van Beneden, 1876)
  • Monotherium delognii (van Beneden, 1876)
  • Monotherium wymanii (Leidy, 1853)

Monotherium is an extinct genus of pinniped belonging to the subfamily Monachinae. It is known from fossils found in the middle to late Miocene of Belgium and the east coast of the United States.


Four species are currently recognized as valid: Monotherium aberratum, Monotherium affine, Monotherium delognii, and Monotherium wymanii. The first three are known for Tortonian-age deposits from Belgium, while Monotherium wymanii is known from the Calvert Formation of Virginia.