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

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

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Anonymous 0 Comments

Mammals have backbones (and associated muscles, of course) that are good at bending sort of “under” the length of the backbone (picture a cheetah running; that backbone is flexing back and forth, helping the back legs move forward and backwards like crazy), where fish have backbones (and attached muscles) that are good at moving “side to side”. When a mammal goes aquatic, that backbone (and muscles) is still best at that same “running like a cheetah” movement, and the new for-water tail works best oriented perpendicular to the backbone’s movement.

Anonymous 0 Comments

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

Anonymous 0 Comments

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.

Anonymous 0 Comments

I’m not sure but I think it’s because marine mammals need to go up to the surface for air, while fish and other don’t. The horizontal tail makes it easier to go up-/and downward. For fish(es?) It is not as important to go up and down.
That’s my guess

Anonymous 0 Comments

The main reason that sea mammals tails are different from fish is that mammals breath air. The default movement of a whale for example is to go up to get air and go back down, while a fish primarily only has to move side-to-side. Whales and dolphins tails evolved from a typical straight tail and their legs became smaller and smaller until they were not longer present.

Anonymous 0 Comments

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.

Anonymous 0 Comments

I don’t actually know but if I had to guess it is because marine mammals were not always marine mammals. They were land mammals originally. If you think about swimming with a pair of legs an up and down motion is significantly easier to do than side to side. Over the course of evolution with small incremental changes, it is fewer changes with more immediate results for the legs and feet to fuse while maintaining the same spine and hip structure that makes up and down motion easier than side to side.

So basically the up and down motion is because marine mammals effectively have legs and feet structure inside their tails where as fish do not.

Compare this to the evolution of fish, their side to side motion fins are flattened out tails instead of fused legs and feet. If you look at many fish they have small guiding fins where there would have been legs. Tail motion works better side to side (watch how an alligator or snake swims) so evolution’s small incremental changes would have favored side to side purely because fish evolved swimming using a tail while mammals evolved swimming using legs.

Anonymous 0 Comments

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Anonymous 0 Comments

The tails in these animals developed completely independently of each other. In the case of fish the tail developed from the tail. And they therefore ended up with this vertical tail. You can see some of the similar features in alligators even though this is a separate development of a swimming tail again. Mammals on the other hand have a tail which have developed from their hind legs. First as webbing between the toes like most aquatic animals but then this webbing grew together and bigger to form the tail you see today. Because of this it ended up horizontal. This advantage of this is that they use the same bone structures as all mammals feet so it is a much shorter development path. However the vertical tail of fishes means they can use muscles along the entire body to swim instead of shorter muscles connected to the rear body as mammals do.

Anonymous 0 Comments

By “other marine life”, do you mean fish? Cos they aren’t mammals obviously. I don’t know of a marine mammal with a vertical tail