Denison (1978) postulates that the genus could be an arthrodire or ptyctodont, but places it in his "incertae sedis" section. Individual specimens tend to resemble the ptyctodonts from the same units and ptyctodonts from Australia, so Deinodus is most likely a ptyctodont. Specimens interpreted as lateral spines may show that Deinodus was a basal ptyctodont, not far removed from the petalichthids (Martin, 2002).