Until recently, sea lions were grouped under a single subfamily called Otariinae to distinguish them from the fur seals Arcocephalinae, based on the most prominent common feature between all species, namely the lack of the dense underfur characteristic of the latter.
Until recently, sea lions were grouped under a single subfamily called Otariinae, whereas fur seals were grouped in the subfamily Arcocephalinae. This division was based on the most prominent common feature shared by the fur seals and absent in the sea lions, namely the dense underfur characteristic of the latter.