From this Flower (1976) concluded that the Ordovician and Silurian pseudorthocerids (sensu Sweet 1964) were derived from different orthocerids (Orthocerida) and were therefore polyphyletic. As a result, true pseudorthocerids were limited to the Pseudorthoceratidae while the earlier Ordovician look-a-likes were retained in the Orthocerida (Michelinocerida Flower)