The northern elephant seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the southern elephant seal). It is a member of the family Phocidae ("true seals"). Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great: The males can grow to and , while the females grow to and . Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.