Fluctuations of the ammonoid diversity during the Late Carboniferous period calculated by using the data stored in the
  database GONIAT reveal three critical intervals in the ammonoid evolution: the time (1) around the Namurian-West-
  phalian (Yeadonian-Langsettian, Halian-Bloydian) boundary, (2) around the Moscovian-Kasimovian (Desmoinesian-
  Missourian) boundary, and (3) the Carboniferous-Permian boundary (CPB).  Several major groups became extinct at
  the respective boundary, and other groups entered after the boundary events.  Relatively few species crossed these
  boundaries.  The quantitative and qualitative analyses of the present study indicate the close connection of the faunal
  changeover with the onset or at least drastic increase of new morphological characters. ln the periods preceding the
  critical intervals a decreasing number of new species, a high number of extinct species and a low rate of species from
  older levels can be observed.  For the time after the critical interval, a general increase of the species frequency, an
  increasing number of new species of different root -roups, as well as an increasing number of long lasting species is
  characteristic.