sentences:  The Posttornoceratidae are derived from the Falcitornoceratidae through "Exotornocers" (Saunders et al.2004)
  
  The family has been split into two subfamilies each containing two genera.Slightly older are the lower to middle Famennian Posttornoceratinae, followed by the later Famennian Discoclymeniinae.