This weakly strengthens the hypothesis by establishing that it is at least possible to store oxygenated blood in the spleen, as shown by horses, another mammal species.

If anything, this would slightly weaken the argument by telling us that many seals already have a built-in \"overflow\" space for extra oxygen. This makes it less likely that Antarctic seals would need to store additional oxygenated blood in their spleens, since they might also be able to store oxygen in their muscles.

This strengthens the argument by telling us that seals do have a need to store oxygen somewhere besides their lungs and bloodstream. The spleen is one potential place for oxygen to be stored.

This strengthens the argument, because it suggests that Antarctic seals spleens’ have some special function related to long dives, which could well be the storage of oxygenated blood.

This strengthens the argument, because it implies that Antarctic seals’ spleens are designed for storing blood.