About 65 million years ago, an asteroid struck Earth, and the dinosaurs that ruled the earth for 160 million years officially withdrew from the stage of history, while birds and mammals began to rise.
With the advent of the Quaternary glacial age (which began about 2.6 million years ago), mammals completely occupied the ecological niche and became terrestrial overlords, with great changes in species, numbers, and body sizes.
However, there is one branch of mammals that is far from being content with land, and they have set their sights on the wider ocean, and that is the cetaceans, which are now whales and dolphins.
Although there are several mammals that now live by the sea, they are called marine mammals, but cetaceans are the first mammals to go to the sea, and the mammals that are the most adaptable to the sea.
Whales can go down to sea at least 50 million years ago, and now they can no longer stay on land, even if only for a short time, they will die like fish.
However, whales and fish cannot stay on land for different reasons.
Fish are because they need to use their gills to get oxygen in the water, once they enter the land can not get oxygen, and whales use their lungs to obtain oxygen in the air, they can not stay on land because they leave the sea, the huge size will make the internal organs be seriously squeezed.
So there's an interesting question, since whales have adapted perfectly to the oceans over 50 million years of evolution, why didn't they evolve gills and instead continue to breathe with their lungs?
Photo note: Sperm whale and its bones
Whales come from land
There is no doubt that whales are mammals, they come from land, and even though they now live entirely in the sea, the bones of their bodies still retain the original appearance of land mammals.
The oldest known ancient whale is the Bucky whale or Pakistani whale, which is known from 50 million-year-old fossils that they have four legs, a tail, and look more like wolves than whales.
These animals have sharp teeth in their mouths, worn in a way that suggests they eat fish.
Picture note: Ancient Whale of Pakistan, a quadruped living in water
What's interesting, though, is that their eyes are above the skull – plus what does that mean?
They may have lived much like crocodiles today, with their eyes above the skull, allowing them to observe the surface of the water even underwater, and to prey on animals that came to drink water at the water's edge.
These ancient whales were able to hunt underwater, and 49 to 40 million years ago an ancient group of whales known as protocyan whales spread across waters around the world.
Caption: Chocobo whales - lived in shallow seas 49 million years ago
Their ears and jaws are maximally optimized for underwater hearing and swimming, although they, like today's seals, return to the land to breastfeed their offspring.
Protocetaceans were very diverse, and over time many of them went extinct, but some were more adapted to the ocean and became today's whales and dolphins.
They have dorsal fins, their limbs are completely covered by "webbeds", and they look similar to "aquatic" sharks, which is called convergent evolution – two completely unrelated species become the same in order to adapt to the same environment.
But even so, why has the essence of the whale that breathes air never changed?
Picture note: Fish breathe with their gills
Breathe with your lungs stronger than your gills
Fish and water seem to be strongly related, so we take it for granted that animals in water should breathe with gills, not with lungs.
In fact, even in the ocean, breathing with your lungs is better than your gills, at least for whales.
Gills allow animals to obtain oxygen underwater, which is a perfect adaptive evolutionary trait. But the oxygen content of water is very low, only 4.59 to 8.72 mm/l for seawater - almost between 4.59 ‰ and 8.72 ‰, and this proportion is 21% in the air (atmospheric oxygen content).
Breathing air allows organisms to get dozens of times more oxygen, and it's clear that breathing with lungs is a more efficient way to breathe, and whales need this oxygen to boost their metabolic rate because they are thermostatic animals.
Photo note: Sperm whales sleep vertically, and they can sleep for 2 hours with one breath
At the same time, this is why the current whale can grow so huge, to know that the largest blue whale can reach 200 tons, if you breathe with the gills, it is almost impossible to maintain the temperature of such a huge body.
Breathing with lungs was something their ancestors had evolved over hundreds of millions of years, whales have no reason to abandon their lungs, and all living things in nature are efficient, and with lungs they naturally won't make a gill again.
However, in order to be able to hunt happily in the water, the whales did make many adaptation changes.
How do whales hunt underwater for long periods of time?
For ordinary people, holding your breath for 1 minute is estimated to be difficult, but a sperm whale can stay underwater for 2 hours, holding its breath until it is finished hunting and returns to the surface.
Whales do this not because they improve the most is not their lungs, or how they get more oxygen, but how they store it.
We obtain oxygen in the air through the lungs, and then transport it through the blood to the whole body, and hemoglobin is used as a means of transporting oxygen, and when we hold our breath, the main thing is to consume the oxygen in hemoglobin to keep us awake for a certain period of time.
Whales are the same, but they have about twice as much hemoglobin in their blood as humans, suggesting they are able to store more oxygen.
Not only that, but their blood content is also much higher than that of terrestrial creatures, and the volume of human blood is about 7% of that of the body, but the blood of whales reaches 10%-20%, which is equivalent to their storage space for oxygen.
Another storage space for oxygen is myoglobin in muscles, which is 30 percent higher in whale muscle than their land relatives, allowing them to store about 35 percent more oxygen.
In addition to storing oxygen, whales are also very good at "saving oxygen", such as consciously controlling their heart rate and reducing blood flow to some non-essential organs and muscles.
In short, it is clear that whales do not need gills, and there are ways to live well in the water, or even better, which is why they do not have gills now, and most likely there will be no gills in the future.