Atopotarus is an extinct genus of pinniped from the middle Miocene known from one specimen (holotype LACM 1376) from Los Angeles County, California.

[4] The only specimen of Atopotarus is an incomplete articulated skeleton preserved in a slab of rock, with material from the skull to part of the spine, ending before the pelvis.

[2] As with other members of its family, Atopotarus possessed large orbits, which would indicate that they relied heavily on eyesight for hunting, and may have been deep divers.

[5] Both Atopotarus and modern eared seals share similarly long and well developed neck structures, which is used to allow flexible movements for hunting prey underwater and swimming.

Notable differences in the skull include an elongated cranium with large crests, lack of a pre-narial shelf, and the elongated mastoid process, where neck muscles attach and blood vessels flow through, which protrudes ventral to level of the postglenoid process.