The Japanese sea lion (Japanese: ニホンアシカ Hepburn: Nihon ashika, Zalophus japonicus) is an aquatic mammal thought to have become extinct in the 1970s. Prior to 2003, it was considered to be a subspecies of California sea lion as Zalophus californianus japonicus. However, it was subsequently reclassified as a separate species. Some taxonomists still consider it as a subspecies of the California sea lion. It has been argued that Z. japonicus, Z. californianus, and Z. wollenbaeki are distinct species because of their distant habitation areas and behavioral differences.