Though it does not know for certain what animal seals evolved from there are theory that it was an animal similar to otter like ancestors. It seems they originated from North Atlantic over 15 – 20 million years ago which is the latest one form sea animals exception of the otter.
There is debate if they evolved from the same animal as otariids (sea lions and fur seal) and walruses.
Seals have evolved from having no odious necks they still have one though and external ears to help them swim through the water. Along with having no exterinal gentila and few limbs. Also the by having blubber it not only helps them keep warm but to swim.
Along with their eyes not only have a protective third eyelid to protect the eyelid from sand and other debris. Their eyes have also adapted to take in more light so in low light areas they can see better. However on land they struggle more with seeing since they eyes are so used to having little to no light.
Seals also devolved to ways to make it so their able to able to hear better underwater and to prevent water from rushing into their ear. One of the ways their ears are different is how they have insulation in their inner ear. Along with when their bones are fused they one of the skull and middle eared are infact delayed this causes for background noise to not reach the ear. Since they have no outer ear to the inner ear form water getting in the muscle around the ear cannel learned to contract to prevent water getting in the ear.
refferce:https://marineanimals.ca/marine-animals/pinnipeds/seal-biology/