Patterns of extinction and recovery of phacopid trilobites during the Frasnian–Famennian (Late Devonian) mass extinction event, Canning Basin, Western Australia

Abstract

AbstractA diverse fauna of phacopid trilobites is described from the Late Devonian (middle Frasnian to early Famennian) of the northern Canning Basin, Western Australia. One new genus and four species in two genera are described from zones 11, 13a and 13b of the middle and late Frasnian:Trimerocephaloides sinevisusgen. nov. and sp. nov.,T.?linguiformissp. nov.,Acuticryphops acuticeps(Kayser, 1889) andA. klapperisp. nov. Late Frasnian phacopines are either blind, as shown for the first time inTrimerocephaloides sinevisus, or show trends to decreasing eye size up to the Frasnian–Famennian ‘Kellwasser’ mass extinction event. This evolutionary trend inAcuticryphopsis demonstrated to have been global at this time. One new genus and six species of early Famennian phacopids are described, from the Uppertriangularis, crepidaandrhomboideazones:Houseopsgen. nov. with the new taxaH. canningensissp. nov.,H. beckerisp. nov. andH.sp. A,Babinops planiventerFeist & Becker, 1997,B. minorsp. nov.,Trimerocephalus tardispinosusFeist & Becker, 1997 andT. mimbisp. nov. In contrast to European sections where exclusively blind phacopids are known in earliest Famennian sites, initial recovery following the mass extinction event in Canning peri-reefal environments is characterized by oculated forms. These trilobites must have evolved from conservative ancestors with normal eyes that had succeeded in surviving the Kellwasser biocrises in reef-related shallow water niches. Thus the origin of post-event phacopids from shallow water environments is demonstrated for the first time. Descendant lineages show increasing eye size, increased cephalic vaulting and effacement during the early Famennian.