Seals and sealions are almost certainly descended from different land-dwelling ancestors. True seals do not have external ears but sealions (and their relations, the fur-seals and the walrus) do have ears. The limbs are also different. Sealions can prop themselves up on their flippers and tuck their hind legs beneath them so that they can move about on land quite well.
Seals cannot rear up and have little use for their hind legs on land. In the water, the seal propels itself largely by its hind legs, whereas the sealion uses its front flippers.