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

Original marine vertebrates (‘fish’) have vertical tails because their spines and musculature developed to move side-to-side to generate forward thrust – a horizontal tail fluke would be useless.

When the descendants of these creatures moved on to land, many of their descendants still retained the side-to-side motion – look at most lizard locomotion, for example.

Mammals developed spines that flexed vertically – this is more efficient in most circumstances for 4-legged forward motion on land. For an extreme demonstration of this, look at the spine of a cheetah when running.

Evolution tends to follow the simplest route and it’s easier to build on existing characteristics rather than go back to the ‘drawing board’. When the ancestors of marine mammals began to evolve back in to the sea, their spines and tails maintained the vertical movement capability so developed horizontal tail flukes to increase thrust.