The way of life on earth and in water is significantly different; for a person, life on land is familiar in the same way as for fish in rivers, seas and oceans. However, in order for the life of aquatic inhabitants to take on a form familiar to all of us, the evolution of fish had to occur.
Millions of years have passed
Water and air have different densities, so moving in water is much more difficult, requiring more energy. However, there are exceptions in the water kingdom, for example, jellyfish are almost 100% water and have the same density with it, which allows them to move around without any special effort.
Fish are much heavier than jellyfish and have a skeleton and muscles. To move in the water, they need to make certain movements, otherwise they would go to the bottom. For millions of years, the evolution of fish took place before they took on the shape we knew.
Big variety
There is a wide variety of fish species, for example, sharks, as well as other fast fish, which can be developed at high speed by the extremities - tail and fins. Their close relatives - manti and flat slopes - are devoid of fins and are not able to develop high speed. Because of this, they spend their whole life near the seabed. Bone fish have a swim bladder, thanks to which they sink to the bottom or rise up.
In other words, the evolution of the skeleton of fish predetermined not only their appearance, but also their way of life. As mentioned earlier, the appearance of the fish was affected by the density of the water, for rapid movement in its depths, the fish acquired a streamlined shape during evolution, which reduces resistance. To balance and direction of movement in fish, the lateral and dorsal fins, as well as the tail, were gradually improved.
From lampreys to chimeras
To date, scientists consider lampreys to be the most primitive, of which 26 species are scientists. These jawless vermiform parasites lack the spine, ribs, and skull. The role of the spine in lampreys is played by the chord - this is the dorsal string. The fossils from the remains of ancient fish, which were found in the earliest layers of rocks during excavations, are reminiscent of modern lampreys (jawless). As scientists suggest, they lived near the seabed.
Fish that had a full skeleton and jaw appeared much later. So, 400 million years ago they are divided into two main types: cartilaginous (stingrays, sharks, chimeras) and bone. It is to the second type that the rest of the fish that we know today belongs.
During the evolution of fish, a lot of unusual and original specimens appeared. For example, a chimera that lives in great depths. She is not like any other fish. This species combines the characteristic features of bony and platelet-gill fish.
Classes and Views
In cartilaginous fish, the skeleton is formed from cartilage, in bone representatives, from bones. This is the key difference in these classes. Currently, about 20,760 species of fish with a bone skeleton, and about 710 species of stingrays and sharks, are known.
Every year, ichthyologists find and describe in detail several of the latest fish species. The origin and evolution of fish is a truly amazing process, full of mysteries, which experts are working on to unravel. An interesting fact is that it is fish that make up the majority of all vertebrates living in the modern world.
Fish evolution processes
Most inhabitants of the seas and oceans today have fin spines in the fin skeleton. In fish that have a bone skeleton, they are immediately evident, and, for example, in sharks, they are hidden under a thick layer of skin. However, the skeleton of coelacanth and horned teeth has an unusual structure, it resembles a human hand, which is why they are called cysteras.
According to scientists, in the process of evolution of the brush-headed fish, lap-finned fish appeared, then the first amphibian vertebrates, and later terrestrial animals. Representatives of the carp-dwellers lived on our planet about 400 million years ago (Devonian period). During evolution, these fish lost their fins, and reptiles, animals and birds came from them. And later, according to one theory, and people.
Who was the first?
However, it is worth noting that basic science is based on hypotheses that have been proposed as a variant of the evolution of fish, and later animals. To date, scientists have not found out exactly who was the ancestor of modern fish. However, most researchers believe that he lived either in water or in places that were periodically flooded.
Nowadays, scientists and researchers are very unlikely to be able to find the oldest form of fish, the so-called progenitor form. This is due to the fact that too much time has passed, almost more than 500 million years.
This time is more than enough to completely destroy any bone tissue that could belong to representatives of the species that gave life to the fish. Also during this period, the fossils of such a creature can naturally be destroyed.
To date, scientists have at their disposal tiny traces that allow us to build hypotheses. However, they can only indirectly confirm one or another version of the researchers.
The available findings are not enough to compile a harmonious, fully proven and factual version of the ancestors of fish. Moreover, for scientists it is still a mystery how, in principle, the evolution of man took place - from fish to humans or vice versa. Yes, do not be surprised, there is such a hypothesis!
Also, for example, like the big bang theory - the concept is very arbitrary, because humanity does not know where and how we came from. That is why inquisitive minds try to explain the origin of everything around them from a scientific point of view.