Prehistoric Fish: Evolution and Timeline

The first prehistoric fish appeared about 530 million years ago. They appeared during the Cambrian Period. These prehistoric fish were the very first vertebrates. Vertebrates are animals with a backbone.

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The Pikaia is an extinct fish from the Cambrian period. In actuality, it is more of a bridge between invertebrates and vertebrates. The fish lacks eyes and a distinct head. However, it had tentacles on its head. It was a small fish no more than 4 centimeters long. Pikaia was flat and probably swam like an eel. Nevertheless, it seems to possess a notochord. A notochord is a rod like structure found in vertebrate embryos.

Conondonta also appeared during the Cambrian period. They are jawless fish that resemble eels. In contrast to Pikaia, these fish had eyes. They were vertebrates and are similar to modern day lampreys. They became extinct about 200 million years ago.

Cosmaspis transvers was an armored jawless fish. They are Ostracaderms – the armored ‘shell-skin’ fish. Their heads are covered with a bony shield. It is likely that armored fish with jaws evolved from the Ostracaderm. These fish became extinct 360 million years ago.

About 430 million years ago, armored fish with jaws began to appear. The Dunkleosteus was an armored predator that could reach a length of 10 meters. These plate skinned fish also had a pair of pelvic fins. Eventually, this may have evolved into the rear limbs of four legged tetrapods. Placoderms also possessed true teeth. Dunkleosteus may have been the first super predator fish. Other Placoderm species were capable of live births.

Acanthodes are known as the spiny sharks. They appeared about 400 million years ago. However, these spiny sharks are not true sharks. Like the Placoderms, they are jawed fish. Real sharks appeared about 50 million years after the Acanthodes. These fish became extinct during the Permian period – 250 million years ago.

Chondrichthyes are cartilaginous fish. They have skeletons made of cartilage instead of bone. Cartilage is tough and elastic tissue that makes up the embryonic skeleton of vertebrates. These fish also have jaws and paired fins. This class of fish includes sharks, rays, and chimaeras.

Dipterus was a lobe-finned fish that appeared about 375 million years ago. The fish have lobe fins and a bony skeleton. Lobe fins are a fleshy appendage extending from the body. Its skeleton has some features similar to four-legged animals. These include bones that are similar to forearms.

The ray-finned fish appeared about 145 million years ago. Ray fins are made of skin supported by spines (rays). Today, almost all fish are Actinopterygii. These are bony fish as well.

Tetrapods evolved from lobe-finned fish about 365 million years ago. Lobe fins are a fleshy appendage extending from the body. In addition, lungfish developed early lungs and limbs. Lungs and limbs enabled lungfish to live outside of water. Regular fish have an air bladder instead of lungs. In this manner, lungfish were a transition from life in the sea to life on the land.