Please note that the content of this book mainly consists of articles that are available online from Wikipedia or other free sources. The Acanthodii, commonly known as spiny sharks, are a class of extinct fish. Systematically, they belong to the superclass Gnathostomata and are the sister group of bony fish (Osteichthyes), together forming the taxon Teleostomi. They are the first fossil-recorded Gnathostomata and lived from the Silurian to the Permian period, reaching their peak during the Devonian. Individual fossilized spines and scales (known as Ichthyodoruliths) have already been found from the Lower Silurian, but secure, well-preserved finds from this time are rather rare. The German name "Stachelhaie" does not imply any relation but refers only to the shark-like appearance of many Acanthodians, characterized by the typical feature that their membranous fins are supported by a spine at their leading edge.