Speaking of fish that can survive on land, I have to think of the blackfish that flooded in the United States, this guy who can breathe with gill organs, but it makes Lao Mei a headache. But there is a fish that is more powerful than a blackfish, do you know what it is?
Blackfish flooding North America
They are lungfish that can survive in the drylands of Africa. Why do lungfish survive on land? How strong is the ability to survive? What kind of evolution did they go through? What is their current situation?
Next, let's understand why the lungfish, which survived the struggle with human ancestors 400 million years ago, can only struggle at the dinner table of the African brother.
Lungfish with a history of 400 million years
"Living fossils" from 400 million years ago
As a vertebrate that can survive in the mud on the arid African land, the lungfish belongs to the species of teleost fish. The earliest fossil record found dates back to the Early Devonian, the first epoch of the Late Paleozoic, dating from 400-360 million years ago.
Devonian paleontologists
Since 1811, British paleontologist James Parkinson was the first to record the fossil stone tooth plate of lungfish. So far, most of the lungfish fossils found are in the Devonian period, and there are 80 genera of lungfish reported, nearly 250 species.
However, there are only three genera and six species of lungfish that still live on Earth, namely the Australian lungfish, the American lungfish and the African lungfish.
The Devonian period was a period of rapid development of vertebrates, during which basically all kinds of fish species have appeared, so this period is also known as the "age of fish".
The Devonian was the age of fish
The struggle with human ancestors
According to Darwin's theory of evolution, the ancestors of humans should be apes. However, Darwin also believed that the ancestors of tetrapods evolved after the ancient fish landed. So modern scientists, after careful study, believe that the ancestors of humans may have been fish that developed into vertebrates in the early days.
Terrestrial vertebrates evolved from fish
- Was the ancestor of mankind the empty spiny fish?
Primitive fish appeared as early as the Cambrian Period 500 million years ago, and later in the Devonian Period they evolved into vertebrates with jaws, primitive fish used the way of eating, and after evolution, they had bones that could bite.
This jawbone is also the bone of the mammalian mouth, so scientists believe that the early evolved teleost fish is the ancestor of mammals.
The most primitive fish
There is also a subfamily of bony fish, carnivotes, and those that can evolve into tetrapods are carnivorous fish. The so-known echinoscetes, lungfish, and tetrapods together make up the suborder Offinchs.
The oldest finfish discovered by scientists to date is known as the Dream Ghost Fish, and from there began its evolution. The empty echinoscephalus was the first to be differentiated, and later scientists found that the empty echinostrel was the closest to the quadruped, and also called it "tetrapod meat finfish".
Quadruped meat finfish
- A struggle with human ancestors
The other differentiated lungfish, although to some extent, did not become the last to evolve into tetrapods, but they were the strongest competitors with the direct ancestors of tetrapods at that time.
During that period, in order to be able to evolve into quadrupeds, they engaged in a series of struggles with the echidna. Earlier we mentioned that the empty spiny fish eventually evolved into tetrapods, and the earliest tetrapod meat fin fish was the strange dongsheng fish, so obviously the lungfish is a step slower.
Ancestral landings of land animals
And later, after the study of mr. Zhang Miman, a mainland paleontologist, he found the earliest primitive type of lungfish - Yang's fish. This fish differs from modern lungfish in that they do not have an inner nostril, so lungfish have not been able to become the ancestors of humans.
Lungfish do not have nostrils
- Lungfish are the closest living fish to tetrapods
But even though the lungfish did not become our ancestor, it still evolved over 400 million years, evolving the inner nostrils and developed lungs, so that it could continue to survive on earth in the future.
After long-term research by paleontologists and vertebrates, it has been found that the fish closest to tetrapods is the lungfish.
Lungfish are related to us
Lungfish that can breathe on land
Earlier we briefly mentioned that lungfish have evolved the inner nostrils and lungs that can breathe on land, how is this structure different from ordinary fish?
It should be mentioned here that after the first fish evolved into vertebrates, in order to live in the water, the gills that modern fish can breathe in the water were evolved. But in the process of evolution, the finned animals were even more powerful, evolving organs that could breathe on land.
Modern fish have gills
This organ is a fish swim bladder with lung-like function, and among the three major extant lungfish genera, the Australian lungfish is the most direct descendant of the lungfish.
In the 19th century, when the director of the Australian Museum, Clivet, was eating lungfish, he discovered its "lung" structure, that is, the swim bladder. So he dissected the lungfish and found that the length of the lungfish was almost the same as its body cavity.
The swim bladder of lungfish is almost equivalent to the body cavity
Moreover, the swim bladder has a special opening and esophagus connection in the pharynx, and there are many small air sacs distributed on it, just like our alveoli. There are also a large number of thin-walled blood vessels on the swim bladder, and when the blood flows through here, it can absorb oxygen from the air of the swim bladder.
He found that the lungfish still breathes in the water with gills, but in addition to the water, it can be replaced with swim bladders. However, there is only one swim bladder in the Australian lungfish, but both the African lungfish and the South American lungfish have a pair of swim bladders, so their ability to survive on land is stronger than that of the Australian lungfish.
Lungfish can breathe oxygen directly into the air
There are still six species of the three lungfish genus, including one each of the Australian lungfish and the South American lungfish, and four species of African lungfish.
African lungfish
Previously, people found a lungfish stuck in the soil for five years in the cracked fields of Africa, it was a Douz lungfish, but miraculously, it did not die.
Fish stuck in the soil
After observation, it was found that the African lungfish made a hole in the middle of the silt during the dry season, like a small bottle, before the mud in the river water was completely dried up.
And lungfish will also secrete a special mucus to make a sunscreen layer for their bodies, so that they will not be grilled into dried fish in the high temperature of more than 40 degrees in Africa. After that, they will spend a 6-month "summer sleep" period in the mud cave.
Lungfish in "Summer Sleep"
During this time, lungfish barely eat or drink, relying entirely on their muscles and fats to meet their needs. Scientists have found that African lungfish slow down their biological centers, so that their metabolism can be reduced to one-sixtieth of the original.
This allows African lungfish to survive in mud caves for a long time, and then when the rainy season comes, they can jump in the river again.
Resurrected lungfish
Reduced to the plate of african brothers
But although the African lungfish has overcome the dry riverbed with its life-saving skills and the wave after wave of heat waves on the African land, it cannot hide from the mouth of the African brother.
The African brother was short of food, and it wasn't a day or two, and when they found out that there was still a fish alive in the cracked land, they almost jumped up with joy. Originally, during the drought period, they lacked food, and the African lungfish almost became a rare food source.
Caught African lungfish
So we can see the African brother in the dry season, running around the dry land to search for lungfish, digging them out of the "summer sleep" like potatoes.
However, because these lungfish are wrapped in mud for a long time, there will be a great smell of mud after digging out. Therefore, in order not to affect the taste, the African brother will deliberately put them in the water for a few days, and then cook the lungfish in the pot after almost no taste.
In nature, African lungfish do not breed until the rainy season, that is, after the end of "summer sleep", probably in January and February or August and September. The female will lay her eggs into the mud nest and then be cared for by the male, if there is no external force to destroy, this way of spawning is naturally very safe, and the survival rate of the juvenile fish will be high.
But it is important to know that African brothers are not only short of food during the dry season, but also come to the river to catch lungfish because of hunger during the rainy season.
Africans fishing during the rainy season
At this time, the lungfish that are spawning will become the plate food of the African brother, and there are enough lungfish that were dug up and eaten during the "summer sleep" period, and as a result, they are now not spared in the river.
As a result, The African lungfish may one day become extinct in such a non-stop killing. However, lungfish have high research value for us, so we should appropriately reduce the damage to lungfish.
Lungfish have high research value
Scientists are still in the ability of lungfish to dormant, perhaps this will have great implications for the dormant warehouse used by humans to travel to space in the future.