Why do most marine mammals have horizontal tails, while other marine life tend to have vertical tails?
In: 75
I’ll fill in some of the good answers I’ve seen here
Whales and dolphins evolved from land animals that had 4 legs. The spine of those animals was built to sit “on top” of the pelvis to help with weight distribution: having the weight be directly above the leg bones meant less muscle strain to keep their weight off the ground. Compare this to crocodiles for example, which still have a horizontally oriented thigh: they don’t spend enough time on land and don’t need to run enough to need that adaptation. They are fine with the little bit of extra work their muscles need to do when they go to land.
Now once you place the pelvis above the legs that way, you can run much faster by stretching out the spine when taking a leap, and then when you gather the legs underneath you the spine flexes.
So you now have a body that uses the spine to help propel itself, and the vertical motion of the spine helps that a lot. So the individual vertebrae and all the muscles attached to them are now being optimised for that vertical movement.
When the dolphins ancestors reverted to the water, they already had that spine that was adapted to vertical movement, and they just got rid of the legs and grew a tail that was along that same axis since they already had the bones and muscles that made that movement easy
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