Acanthodians (Spiny Fish)

The acanthodians are a poorly understood group of extinct jawed fish that are distinguished by the bony spines projecting in front of their fins and by minute diamond shaped scales. There is some dispute over their systematic position because they have features of both bony fish ( Osteichthyes) and cartilaginous fish (Chondrichthyes). They possessed small teeth that were typically confined to the lower jaw; some were toothless. They possess highly advanced, spindle-shaped bodies thought to have made them swift swimmers

Acanthodians are among the earliest jawed vertebrates known. The oldest acanthodian lived during the late Ordovician. They reached their peak during the Devonian, and became extinct during the Great Dying of the end-Permian extinction.

Acanthodians were generally small sharklike fishes varying from toothless filter-feeders to toothed predators. They are often classified as an order of the class Placodermi, another group of primative fishes, but recent authorities tend to place the acanthodians in a class by themselves (class Acanthodii) or even within the class of modern bony fishes, the Osteichthyes. It is commonly believed that the acanthodians and the modern bony fishes are related and that either the acanthodians gave rise to the modern bony fishes or that both groups share a common ancestor.

A most interesting and informative website that gives more information on the Acanthodians and indeed life in the Devonian Period in general is Devonian Times. Although describing things in the Devonan the site tells the story and is devoted to an amazing Devonian exposure called Red Hill in Pennsylvania, USA. Definately worth a look!