The late Devonian trilobite crises

Mid‐Devonian to end‐Late Devonian trilobites of different taxonomic categories are updated as to their actual stratigraphical range with respect to the internationally defined stage boundaries. The main palaeogeographical and ecological occurrences are summarized. Numerical analyses emphasize the clear relationship between fluctuations in diversity and global eustatic events. Already declining in diversity from the early mid‐Devonian, shallow‐water communities became most restricted during the mid‐Givetian Taghanic transgression. After a phase of adaptive radiation, off‐shore trilobite communities were severely affected during the mid‐ and end‐Late Devonian crises. From an initial 5 orders 3 were lost at the end‐Frasnian Kellwasser crisis while only 1 from the remaining 2 orders survived the Devonian‐Carboniferous boundary Hangenberg event. In both cases extinction was preceded by a unidirectional evolutionary trend in eye reduction accompanied by impoverishment of lower rank taxa. This phenomenon is obviously a result of selective adaptation under constant long‐lasting environmental influences. Specialization to obligate epi‐ or even endo‐benthic life habit, however, led fatally to extinction when stable conditions became substantially perturbed. Sudden sea‐level changes with subsequent break in the REDOX‐equilibrium took place at the Kellwasser and Hangenberg events, which were most probably responsible for trilobite mass extinctions.