Palaeonisciformes is an extinct order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of early ray-finned fishes (Actinopterygii). It is not a natural group, but is instead a paraphyletic

Paraphyly

A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...

 assemblage of the early members of several ray-finned fish lineages. It has traditionally encompassed most Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

 actinopterygians, except those that exhibit strange body forms (such as the deep-bodied Platysomoids, or those assigned definitively to any of the living groups of ray-finned fishes.

Andreolepis hedei

Andreolepis hedei

Andreolepis hedei, an extinct prehistoric fish, has proven so far to be the earliest-known Actinopterygiian, living around 420 million years ago. It inhabited Russia, Sweden, Estonia, and Latvia.-References:**...

has proven so far to be the earliest-known Actinopterygiian, living around 420 million years ago (Late Silurian in Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, Estonia

Estonia

Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...

, and Latvia

Latvia

Latvia , officially the Republic of Latvia , is a country in the Baltic region of Northern Europe. It is bordered to the north by Estonia , to the south by Lithuania , to the east by the Russian Federation , to the southeast by Belarus and shares maritime borders to the west with Sweden...

. Actinopterygians underwent an extensive diversification during the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

, after the end-Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 Hangenberg extinction.