Why do most marine mammals have horizontal tails, while other marine life tend to have vertical tails?

Question

Why do most marine mammals have horizontal tails, while other marine life tend to have vertical tails?

In: 75

Answer 1

Reading this thread was really interesting, I always thought it was because marine mammals required oxygen so tails that propelled them up to the surface made sense, where as fish don’t require oxygen so tails that propel them forward makes the most sense.