4SEAS

Evolution of fishes occurred over a long period of time. According the oldest known fossil remains, the fishes already lived in the early Cambrian, that is about 530 million years ago. Ancient fish slightly resembled the modern one. The shell-skinned Ostracoderms that lived in the Ordovic period had neither air bladder, nor skeleton, as scientists suggest, and were very clumsy while swimming. In the Silurian there were already a lot of Armoured fishes, from them descended Placoderms, from them - the ancestors of Acanthodii, sometimes called spiny sharks, Lat. Acanthodii) and Cartilaginous fishes ( Lat. Chondrichthyes). In the Silurian fish first appeared jaws and teeth.

In the Devonian fish were already numerous and quite varied. Among them there were as rather peaceful species that passively feed filtering the sludge (Jawless Armoured fishes), as well as active predators (plakodermy (born Placoderms, Lat. Placodermi)). The size of fishes ranged from a few centimeters to 10 meters and more. New groups of fish develop, each of them evolved depending on environmental conditions in particular type of waters. In the mid-Devonian Lungfish (Lat. Dipnoi) emerged. They had primitive lungs which dipnoi could use for breathing air that was very useful in times of seasonal drying of the waterbasins.
During the Devonian period the ancestors of cartilaginous ganoids (Lat. Chondrostei), emerged from dipnoans (lung-fishes; Lat. Dipnoi), emerged Lobe-finned Fish (Lat. Crossopterygii), and from the last ripidistii (Eng, Lat. Rhipidistia).

Further, in the Cretaceous, the Ray-finned fishes (Lat. Actinopterygii) and Lobe-finned Fish, or Fleshy-finned fish (Lat. Crossopterygii), freshwater sharks; Lampreys, or sucking-fishes proliferated. During the same period the number of spiny sharks "shell-skinned” fish and Placoderms reduced significantly.

During the next period, the Permian, spiny sharks and ripidistii disappeared, the number of lung-fishes , freshwater sharks and Bradyodonts decreased. Environment conditions of that period allowed cartilage ganoids to flourish and contributed to the emergence of the first bone ganoid fish (genus Holostei).

Next Era - Mesozoic and its first period, Triassic, witnessed the emergence of paleonisks (Latin Palaeonisci), whose body was covered with rhombic scales. Freshwater sharks Bradyodonts disappear, number of lung-fishes and Fleshy-finned fishes decreased. However, the emergence of bony fish (born Teleosts, Lat. Teleostei) during this period was the important stage in the evolution of fish.

In the Jurassic and Cretaceous periods the bony fish increasingly replace and sharks.

During the Neozoic era, most fish groups acquire up-to-date image.