Question

How did vertebrates evolve?

Answer 1

Evolution is said to be the change of the characters in a species which does not take place suddenly but it is a gradual process. This change taking place is said to be dependent on natural selection. Due to the process of evolution the organisms are believed to have developed to the present forms.

Complete answer:
For brief knowledge of the evolution of vertebrates, one should first know the characteristic features of vertebrates and what they actually are. The vertebrates are a very important group of animals which comprises mammals, birds, reptiles, amphibians and fishes. Vertebrates are further divisions of chordates due to the presence of vertebral columns. The well-known characteristic feature of vertebrates is presence of notochord, pharyngeal slits, hollow nerve cord and presence of post anal tail is also seen.
The first existing vertebrates were the jawless fishes which include in the subclass agnatha. Their bodies are covered by hard bony plates and from the name itself we can understand that they are fishes without the presence of jaws. These early fishes lack paired fins. The early jawless fishes no longer exist but some species of fishes that lack jaws like the very popular hagfish still exist. The hagfish is not directly related to agnathans but it is related to cartilaginous fish. The later development was so that the fishes lack jaw bone but had paired fins the armored fish are the best example for this.
Then gradually cartilaginous fishes came into existence. These types of fishes have skeletons made up of cartilage rather than that of bones. They also lack swim bladders and lungs if we compare them with other fishes.
The next which came into existence were the amphibians. They were the first vertebrates that could survive on land too. The early amphibians had many fish-like characters but they lost the characters with time, but amphibians underwent larval phases that were entirely aquatic characters.
After amphibians, reptiles, birds and mammals evolved having few characteristics which were peculiar.
The reptiles have characteristic features like presence of scales, eggs covered with a hard shell, legs which are strong beneath their body. They are usually crawlers.
Birds have feathers unlike other vertebrates and hollow bones.
Mammals have hairy bodies, are warm blooded and have mammary glands too.
Hence from the discussion it can be concluded that the evolution of vertebrates is a very gradual process with changes occurring species to species.

Note: Evolution is divided into three main types that are divergent evolution, convergent evolution and parallel evolution.
-Divergent evolution: It is a type of evolution in closely related species.
-Convergent evolution: This is a type of evolution where close related species evolve traits to adapt to the surroundings.
-Parallel evolution: In this type evolution takes place in distinct species but with the same origin.