The wide speciation of ammonoids in the Upper Viséan and Lower Namurian represents
  one of the great events in their Palaeozoic record and is recognized in all Carboniferous
  sequences world-wide.  A study of the Central Asian successions revealed great taxonomic
  diversity of the Lower Namurian ammonoids comparing that of the South Urals.  The basic
  geometry of the ammonoid conch (described by three fundamental parameters: whorl ex-
  pansion rate, degree of the whorl overlap, and whorl shape), and the shell ornament were
  used to reveal the patterns of ammonoid morphological diversity in the Lower Namurian
  successions in Central Asia, to make comparisons with other regions.  A total of 87 species
  belonging to 48 genera were used.  They were represented by 563 specimens from over 40
  localities in the middle and southern Tian-Shan, southwestern Gissar, and southwestern
  Darvaz.  Namurian ammonoids in Central Asia exploited almost all conch morphologies
  previously recognized in other successions.  Throughout the Lower Namurian the preferred
  morphologies were represented by the involute and moderately evolute conchs with a low
  whorl-expansion rate.  The distribution of the morphologies throughout the successions
  shows great similarity to that of the South Urals and resembles to some extent those of
  North America.  The range of morphological diversity may be different in the lithologically
  similar successions (shallow-water limestones show different proportions of some mor-
  photypes in Central Asia and in the southem Urals).