*THE FIRST VERTEBRATES*

   Vertebrates are a species closely related to all vertebrates.These are commonly referred to as *jawless fish* .They had a vertebra that was a feature that no  previous animal had.Considered to be the first vertebrates, these jawless fish have been discovered by paleontologists. *Kiaeraspis* is one such fossil found entirely in a (400 million)-year-old, flat-bottomed fish.It had two skeletal structures on the outside as well as on the inside.Their groups entered the freshwater rivers from the sea and inhabited them.

   Although almost all of these jawless fish have disappeared, several species remain today. *Lamprey* is one such.It is a parasite that clings to the body of a fish by sucking on the blood through its mouth.

   The *Silurian* period was the period when jawless fish were common.By the end of that period and the approach of the *Devonian* period, these fish had made great strides.That is, they have jaws.Scientists named the first jaw fish *Placoderm* .The  *Climatius*  fish is an example.These fish had a brain sheath, gill arches, spinal column and an external skeleton.

   Then out of these fish came spiny fish and cartilage fish. *Climatius* was a cartilaginous fish that lived then. *Cheirolepsis* is one of the thorny primitive fish that lived at that time.It is the ancestor of modern fish with thorns.

   Of these, the spiny fish had the feature called lung.Because they had lungs, they could come out of the water and stay on land longer.Scientists believe that fish with lungs became extinct (70mlns)years ago.But in 1938 a living fossil like a fish with lungs was captured off the coast of South Africa.It got the name *Coelacanth* .

   Fourteen years later, in 1952, a fish of the same species was caught off the coast of Madagascar.Scientists called it *Latimeria* .

       By the end of the Devonian period, the earth's seas, lakes, ponds, canals, and streams were overflowing with fish.