Arthrodiran is a term used to describe a group of extinct armored fish that lived during the Devonian period. Due to its complex nature, alternative terms have been used by scientists to describe them. One common synonym is "placoderm," which refers to the distinctive bony plates that covered their heads and bodies. Another synonym is "arthrodire," which emphasizes their unique jointed head armor that allowed for greater flexibility and range of motion. They have also been called "dunkleosteid" after the famous paleontologist Dr. Edward Drinker Cope who discovered them. Regardless of the term used, arthrodirans represent a fascinating and important group of ancient fish that played a significant role in the evolution of vertebrate life.