The ammonoid crisis at the Devonian-Carboniferous Boundary (DCB) not only resulted in the extinction of ammonoid
stocks but also  in a paradigm shift of ammonoid morphotypes.  During the late Famennian, below the DCB two ammonoid
orders proliferated: the Clymeniida, with a dorsal siphuncle and mainly evolute and frequently ornamented conchs, and
the Goniatitida, displaying an advanced involute smooth conch form.  In the short "Stockum interval" immediately below
the DCB, almost all prevalent stocks  became extinct except for a few non-ornamented forms with evolute inner whorls.  
They gave rise after the DCB to smooth and ornamented Goniatitida with a triphasic mode of ontogenetic conch
development and evolute ontogenetic growth stages, and to the new order Prolecanitida with discoidal evolute
non-ornamented conchs.  The fluctuation of ammonoid faunas in the critical interval around  the DCB showed a rapid
decline in diversity and a short low point with only one morphotype, and after the DCB a gradual diversification in
several directions.  The possible causes of this pattern are discussed.