Question

evolution of bony fishes explained

Answer 1

The bony fishes gradually evolved from the cartilaginous fishes around 420 million years ago. It is found that the fishes were first vertebrates that were found millions of years ago and gradually it led to evolution of many organisms. During the Cambrian period, it was when the fish had no jaws neither vertebrates and this was around 490 to 540 million years ago. And during this phase, the fish was known as the Agnatha. As it gradually evolved it started developing four components and was the beginning of evolution of a true fish which is called the Pikain. This had a bilateral symmetry along with V-shaped muscles and nerve cord. Gradually it entered the Ordovician Period, around 443 – 488 million years ago, the first signs of jaw and vertebrate developed. In this period, jaws were developed for the fishes. This led to formation of the Astraspis which no jaws and its body was covered in scales. By the end of the Palaeozoic period, the fishes started evolving and started developing jaws and were called Pincoderms and Acanthodil. However, about 416 to 443 million years ago, the fishes entered the Silurian Period and the jaws evolved even further. This gradually led to the development of the cartilaginous fish and bony fishes which are called as Chondrichthyes and Osteichthyes, respectively. During the Devonian Period, the bony fishes evolved gradually around 358 to 419 million years ago. After that the fishes enters the Permian period leading to the mass extinction of fishes and it led to elimination of around 96% of the marine population. After that it started the Mesozoic Era from 56 to 251 million years ago and it led to gradual evolution and developing of bony fishes called Osteichthyes and they recovered after the Permian period was over.