The way of life on land 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 the 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, more energy costs are required. 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 much 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. Fish evolved over millions of years before they took on the shape we know.
Great variety
There are a wide variety of fish species, such as sharks, as well as other fast fish, which allow high speed to develop limbs - tail and fins. Their close relatives- manta rays and flat rays - are devoid of fins and do not have the ability to develop high speed. Because of this, they spend their entire lives at the bottom of the sea. Bony fish have a swim bladder, thanks to which they sink to the bottom or rise to the top.
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 fish was influenced by the density of water; in order to quickly move in its depths, fish acquired a streamlined shape during evolution, which reduces resistance. For balancing and direction of movement, the lateral and dorsal fins, as well as the tail, were gradually improved in fish.
From lamprey to chimera
To date, scientists consider lampreys to be the most primitive, of which there are 26 species by scientists. These jawless worm-like parasites lack a backbone, ribs, and also a skull. The role of the spine in lampreys is played by the chord - this is the dorsal string. 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 at the bottom of the sea.
Fish that had a complete 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. For example, a chimera that lives at great depths. It is not like any other fish. This species combines the characteristics of bony and lamella-branch fish.
Classes and types
In cartilaginous fish, the skeleton is formed from cartilage, while in bone representatives - from bones. This is the key difference in these classes. Currently, about 20,760 species of fish with a bone skeleton are known, and approximately 710 species of rays and sharks.
Every year, ichthyologists discover and describe in detail several of the newest fish species. The origin and evolution of fish is a truly amazing process, full of mysteries that experts are working on. An interesting fact is that it is fish that represent the majority of all vertebrates living in the modern world.
Processes of fish evolution
In most of the inhabitants of the seas and oceans today, the skeleton of the fin is spikes lined up in a row. In fish that have a bony skeleton, they immediately catch the eye, and, for example, in sharks, they are hidden under a thick layer of skin. However, the skeleton of coelacanths and horned teeth has an unusual structure, it resembles a human hand, which is why they are called crossopterans.
According to scientists, in the process of evolution of lobe-finned fish, lobe-finned fish appeared, then the first amphibious vertebrates, and later land animals. Representatives of the lobe-finned animals lived on our planet for about 400 million years.ago (Devonian period). In the course of evolution, these fish lost their fins, and reptiles, animals and birds originated from them. And later, according to one of the theories, people.
Who was first?
However, it is worth noting that fundamental science is based on hypotheses that were proposed as a variant of the evolution of fish, and later animals. Until now, scientists have not figured out who exactly was the ancestor of modern fish. However, most researchers believe that he lived either in the water, or in those places that were periodically flooded.
In our time, scientists and researchers are extremely unlikely to be able to find the most ancient 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 is more than enough time for the complete destruction of any bone tissue that could belong to representatives of the species that gave life to fish. Also during this period, the fossils of such a creature can be naturally destroyed.
Today, 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 finds are not enough to make a coherent, 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 man orvice versa. Yes, do not be surprised, there is such a hypothesis!
Also, for example, like the big bang theory - the concept is very conditional, because humanity does not know where and how we appeared. That is why inquisitive minds are trying to explain the origin of everything around from a scientific point of view.
