Detailed analysis of Upper Devonian ammonoid evolution and palaeo-
 biogeography enables the minute recording of global palaeoceanographic
 changes such as anoxic events and eustatic fluctuations during a time of
 global greenhouse climates.  Major improvements in biostratigraphy and
 taxonomy allow the distinction of 36 genozones building on and adding to
 existing zonal schemes.  The ranges of 177 genus-level taxa are reviewed to
 estimate diversity changes, origination, and extinction rates.  Within the
 Upper Devonian to earliest Carboniferous twenty evolutionary phases are
 distinguished and the Upper Kellwasser and Hangenberg mass extinctions
 are the most pronounced events.  Transgressions generally led to diversi-
 fication while regressions caused diversity reductions.  This suggests great
 significance for the 'species-area effect' and the degree of viability of
 migrational routes to allow the spread and survival of allopatric taxa.Short-
 term global anoxic overturns did not affect the overall diversity but led to
 spreads of ammonoid biofacies into usually uninhabitated areas.  Associated
 with hypoxic incursions are revitalizations of bradytelic lineages that must
 have survived in low-oxygen deeper-water refuges.  Phases of the Frasnian-
 Famennian and Devonian-Carboniferous boundary biocrises show simi-
 larities with small-scale events.  Judged from the viewpoint of ammonoid
 evolution, both mass extinctions appear to be multiphased sudden eustatic
 and anoxic events that prevented recoveries even for a considerable while
 after return to normal oceanographic conditions.  The model developed
 requires common mechanisms to explain the observed short-term evolu-
 tionary disruptions of different magnitude.  Ultimate causes may have
differed much from observed recent to subrecent processes making
actualistic comparisons unhelpful.