#acanthodian

• Acanthodian — A fossil representative of the extinct class Acanthodii, a group of ancient jawed vertebrates (gnathostomes), considered among the earliest to possess jaws, which inhabited global waters from the Silurian to the Permian periods. Popularly termed 'spiny sharks', these small primitive fish were characterized by a partially cartilaginous skeleton and, definitively, by the presence of stout, rigid bony spines located at the leading edge of all their fins, serving for structural support and predator defense.