adapted to breathing air? The evolution of
is an important process of species reproduction and development, and the species gradually evolves suitable conditions for survival as the environment changes. We know that the early species on the earth lived in the ocean and then gradually developed on the land. What is curious is how did the first creatures on the earth that migrated from the water to the land adapted to breathe the air? After all, they are used to the breathing method of the ocean, , so how do they adapt to the mainland?
To answer this question, we must first have a general understanding of fish's breathing. In fact, the way of breathing in the ocean and on land is the same. For example, because the oxygen content in the air is much more stable than that of water, fish can swim to the surface of the water and swallow a large mouthful of air, and then the oxygen is dissolved into the blood through the stomach. Once a fish evolves this behavior, it is not difficult to imagine how the stomach becomes specialized to improve air breathing, first growing a small part of it to breathe air, and then further developing into the lungs. This swallowing behavior is It is still quite common in various fishes.
In fact, about 400 million years ago, most fish such as bony fish had lungs, so they could use atmospheric oxygen to supplement the oxygen dissolved in water. But what happens next in a fish species is that the lungs are further specialized into a swim bladder, allowing them to better control buoyancy, and in fact their body is completely isolated from the outside air source, relying on the gas dissolved in the blood. Supply them. The reason for the emergence of
may be because this bloodline also evolved the aorta, which improved their circulatory system’s ability to supply oxygen to the heart and offset some of the need for supplemental oxygen. But whatever the reason, the lineage of this fish, ray fin, or bony fish, became very successful. Not only are they the most successful fish lineage to date, accounting for 96% of all existing fish species, but they are also the most successful among vertebrates. So, even if you find the diversity of lungs in the lineage of modern fish, such as bow fins, bikier fish, gal fish and the named lungfish , the huge success of bony fish means that swimming bladder is now a The standard, not the lung.
However, there are still many potential aquatic habitats without a reliable high oxygen content, especially in tropical freshwater. But evolution is basically a one-way street. A bony fish is unlikely to restore its swim bladder to lungs, just as we restore ears and tonsils to gills. Therefore, in order for Boneless Dragon bloodlines to break into these habitats, they need to evolve new breathing methods.
This type of supplemental air breathing has actually evolved several times in bony fish. One of the most famous examples is the suborder Panoramica, such as fighting fish. This fish has evolved something developed from the gill cavity. The gill cavity is a pocket full of folded bony plates. With a surface area for good gas exchange, betta fish rely on these organs to breathe, so much so that they actually drown without air.
All this is to illustrate that the first creatures that migrated from water to land did not have to adapt to breathing air. This ability had evolved in fish long before the first quadruped climbed onto the mudflat. Air breathing was originally used as a means to obtain supplemental oxygen, which not only helps to survive in hypoxic aquatic habitats, but also helps support a more active lifestyle. Even if the most successful fish lineages lose this ability, when their lungs become specialized swimming sacs, this ability is so important to certain aquatic environments that their offspring have evolved new air-breathing abilities. Way, breathing air is just a fairly common ability in fish.
Of course, although this answer focuses on vertebrates, there are many other animals that transition from breathing water to breathing air. Almost any trip to the beach will find a large number of crabs in the water or on land, and there are many other crustaceans from water to land, from isopods to insects to turtles.
Anyway, even now, there are still creatures in this transition. For example, the loach is a fish that can live on land. This is just an example. Any amphibian is another similar example. All creatures that have existed, including humans who wander on the surface of land today, Are all transitional creatures.
So this question is largely related to what the lungs are and how oxygen is absorbed through the skin. In particular, the distance between the air from the outer membrane to the internal organs and cells must be considered. Every generation uses the lungs more and more. Oxygen is sucked out of the air.
Interestingly, almost all marine fish come from freshwater ancestors. After all the saltwater fish (in the ocean) died, some freshwater fish settled in the ocean again and developed lungs. In hypoxic fresh water, these fish form an internal space that allows them to stick their heads out of the water and get oxygen from the air.
However, the polluted ocean now kills saltwater fish that cannot get oxygen from the air. After some freshwater bodies are connected to the saltwater bodies, some freshwater fishes adapt to the ocean again. The lungs are no longer needed, the lungs re-adapt to become a swim bladder, making their offspring more agile and better adapted to survive.
