Rhinopteraspis is an extinct genus of pteraspidid heterostracan agnathan. It has been previously described as being an elasmobranch, an agnathan, and an antiarch. Furcacaudidae is a family of thelodontid agnathan from the Lower Devonian. One of the earliest known armoured agnathan ("ostracoderm") vertebrate, "Arandaspis", dates from the Middle Ordovician. As with many agnathan groups, heterostracans had no fins besides the tail or caudal fin.