Whereas whales are most closely related to hoofed animals like cows and deer and seals are most closely related to bears and weasels, The majority of DNA studies have shown that the closest relatives to the sirenians are the elephants. This is because they are a separate group of animals that evolved to an aquatic lifestyle on there own. But as the only fully aquatic herbivorous marine mammal they have had to over come challenges not faced by the whales and seals.