Palaeoniscida Moy-Thomas & Miles 1971 The Palaeonisciformes, commonly known as "palaeoniscoids" (also spelled "paleoniscoid", or alternatively "paleoniscids") are an extinct grouping of primitive ray-finned fish (Actinopterygii), spanning from the Silurian/Devonian to the Cretaceous.

Lev Berg erected the superorder Palaeonisci, in which he included early actinopterygians that belonged to neither Chondrostei nor Polypteri (Cladistia).

Mostly following Berg, Jean-Pierre Lehman grouped the Actinopterygii into 26 orders, among others the Palaeonisciformes with the two suborders Palaeoniscoidei and Platysomoidei.

Palaeoniscoidei have traditionally encompassed most Paleozoic actinopterygians, except those that exhibit atypical body forms (such as the deep-bodied Platysomoidei, or those assigned securely to any of the living groups of ray-finned fishes.

In order to make the Paleonisciformes, Palaeoniscoidei or Palaeoniscidae monophyletic, these terms should only be used in a strict sense, i.e., when referring to the clade of actinopterygians that includes Palaeoniscum and the taxa closely related to it.

[11][12][13] Due to the delicate nature of fossils of ray-finned fishes and the incomplete knowledge of several taxa (especially with regard to the internal cranial anatomy),[13] there is still no consensus about the evolutionary relationships of several early actinopterygians previously grouped within Palaeonisciformes.

Andreolepis hedei, previously grouped within Palaeonisciformes, has proven so far to be the earliest-known actinopterygiian, living around 420 million years ago (Late Silurian in Russia, Sweden, Estonia, and Latvia.