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Why Tail of Whale not Wagging Horizontally but Vertically?

Reason for Tail of a whale not Wagging Horizontally but Vertically

But there are also some creatures that return to life in the ocean after landing on land, such as today's whales, or ichthyosaurs in the dinosaur era. It is very strange that the body structures of whales and ichthyosaurs are also significantly different when returning from land to the sea: the tails of whales are flat, while the tails of ichthyosaurs are upright like fish. .

Life comes from the ocean, and today's terrestrial creatures all come from the ancestors of the ocean. But there are also some creatures that return to life in the ocean after landing on land, such as today's whales, or ichthyosaurs in the dinosaur era.


It is very strange that the body structures of whales and ichthyosaurs are also significantly different when returning from land to the sea. The tails of whales are flat, while the tails of ichthyosaurs are upright like fish.


What factors caused the difference between the two, and what logic played a guiding role in the evolution of animals?

In fact, there is one of the most common misunderstandings about biological evolution, that is: animals evolve into a certain form in order to achieve a certain purpose, that is to say, it is a teleological explanation of evolution. In fact, the current research believes that evolution is actually accidental: biology does not actually evolve to achieve certain characteristics, and all evolution is beautiful accidents.


The mammoth didn’t look at the weather forecast and knew that it had to cool down before evolving its long hair. It only grew long hair by accident, and then the climate became colder, and it survived (similarly, the day after tomorrow’s hotter, it will die). 

When the ancient ape came down from the tree, it was not to evolve you and me next to the computer, but after the Neanderthals fell, our kind of humans barely survived.

We have now evolved Natural immunity to many viruses is not deliberate, but those who are not immune are killed by the virus and have no chance to leave offspring.


Knowing this, we can start the following topic.


Why is the tail of a whale flat?

There are many different inferences about why the whale’s tail is flat. The most widely known is this:


A: Whales need to return to the surface to breathe regularly. After breathing, they dive into deep water to prey. The flat tail is convenient for the whale to swim up and down.

This is a typical teleological explanation of evolution. It must be admitted that at first glance, this inference Li Jufu: For example, whales such as sperm whales do need to dive into the seafloor as deep as 3000 meters to hunt the king squid. 

Whales do not have a swim bladder, and their diving is driven by their tails. The flat tail seems to be more conducive to diving.

Tail of Whales

(The attacking sperm whale, target, 1000 meters under the sea)

However, it is easy to find that this kind of inference is not tenable through simple inferences.

For example, why do some whales that only live in shallow waters (such as most freshwater whales whose habitat environment is less than 10 meters deep) also evolved flat tails? 

If deep-water whales have evolved flat tails for the purpose of "facilitating snorkeling" and shallow-water whales have no such demand, why did they "choose" such an evolution?

And a more powerful counterexample is what the subject said-ichthyosaurs. It is also breathing with lungs and returning to the sea from land. There are also a large number of ichthyosaurs who need to dive to a certain depth to find food and also need to surface to breathe. 

Why didn't ichthyosaurs evolve flat tails?

Let’s take a look at why these two creatures returning from land to the sea have embarked on different evolutionary paths.


The appearance of the ichthyosaur is very abrupt, and there have not been enough fossils to explain the detailed evolution of the ichthyosaur. We can only speculate that at the beginning of the Triassic, a certain reptile that had adapted to life on land did not know why it returned to live in the water, and then adapted to this environment well and once became the overlord of the sea.


From the movement of the limbs on land to the tail drive in the ocean, the change in the way of movement is the most powerful proof that ichthyosaurs have adapted to marine life.

However, despite this, the tail of the ichthyosaur has not evolved like fish


(In the early Gejin ichthyosaur, its tail is obviously not like a fish tail, but more like the tail of a lizard. The driving efficiency of this tail is relatively poor)


(It can be seen that with the evolutionary process, the tail fin of ichthyosaurs has become more like fish. But the skeletal structure of the tail fin is still similar to the tail of a lizard. The upper branch of the tail fin has no bone support)


(The bones of fish are completely different. You can see that the tail is supported by bones, called coccyx bone or subcaudal bone)

Obviously, we can find the tails of ichthyosaurs and real fishes. Although they look similar, they are actually quite different. Fish’s tails are supported by bones up and down, while ichthyosaurs only have bones at the lower fork of the tail, and the upper fork is just a fleshy bump. 

In essence, the tail of an ichthyosaur is just a deformed version of the tail of a reptile.

Looking back at the tails of whales, are there bones in their flat tails?

The answer is: also no!

In this way, we can easily come to a conclusion: any evolution tends to improve on the existing basis. Evolve on the existing basis, be more efficient, and have more opportunities to survive.


In this case, the differences in the existing foundation may lead to differences in the direction of evolution


The mammalian ancestors of whales, the transverse process of the spine is larger, and the spinous process is relatively small. 

The muscles attached to the spinous process and the transverse process are more conducive to driving the spine to swing up and down. 

The structure of the spine also determines the mammalian spine. 

The swing back and forth can also be greater (so people can curl up into a ball, but not to the sides)


As for the reptile ancestors of ichthyosaurs, the spinous process is larger in the structure of the spine, and the muscles attached to the spinous process are stronger, which is more conducive to tail lateral swing. We believe that it likes to sway itself before going into the sea.  

As creatures that also returned to the sea from land, the ancestors of ichthyosaurs and whales must have experienced the stage of paddling with their limbs and assisted by their tails. 

When the tail assists in the stroke, it must be the easiest posture. The bone and muscle structure of the ichthyosaur's ancestors determined it to swing from side to side with its tail, and the bone and muscle structure of the whale's ancestors determined it to swing up and down with its tail. 

The vertical and horizontal tails began to differentiate from this day.


Having said that, we understand that fish, whales, and ichthyosaurs are three different tail drive structures. These differences are caused by differences in bone and muscle structure.


Some students may have to ask again: they understand the truth, but which one is better?

Again, there is nothing good or bad, as long as these creatures can adapt to the evolution of the new environment, it is appropriate. In fact, in addition to the tail drive of whales and ichthyosaurs, there are also the limb drive of plesiosaurs and sea turtles, and the hind legs of sea lions and seals. These are all very successful evolutions.

Author: Naval Kishore

Education: Masters Degree in Actuary

The author is an Actuarial expert with 20 Years of Work experience in Fisheries work


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