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

Abstract

A 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 sinevisus gen. nov. and sp. nov., T. ? linguiformis sp. nov., Acuticryphops acuticeps (Kayser, 1889) and A. klapperi sp. nov. Late Frasnian phacopines are either blind, as shown for the first time in Trimerocephaloides sinevisus, or show trends to decreasing eye size up to the Frasnian–Famennian ‘Kellwasser’ mass extinction event. This evolutionary trend in Acuticryphops is demonstrated to have been global at this time. One new genus and six species of early Famennian phacopids are described, from the Upper triangularis, crepida and rhomboidea zones: Houseops gen. nov. with the new taxa H. canningensis sp. nov., H. beckeri sp. nov. and H. sp. A, Babinops planiventer Feist & Becker, 1997, B. minor sp. nov., Trimerocephalus tardispinosus Feist & Becker, 1997 and T. mimbi sp. 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.

Oxic facies and the Late Devonian mass extinction, Canning Basin, Australia

“…Detailed taxonomic work on key fossil groups shows marked reductions in the latest Frasnian, producing gradual to stepwise patterns with two prominent extinction phases at the base of conodont Zone 13a and within the latest Frasnian (Fig. 2;Becker et al, 1991;Becker, 2000;Feist et al, 2009;McNamara et al, 2009;Feist and McNamara, 2013). These studies have linked the two phases to the global Kellwasser events, although Becker (2000) associated massive faunal losses in ammonoids at the base of Zone 13a with a signifi cant regression just prior to the global lower Kellwasser event.…”

An unusual occurrence of Pedinopariops (Trilobita: Phacopidae) within siliciclastic facies in the Devonian of Awaynat Wanin, Libya

“…Our specimen suggests that this ecological limitation may not have persisted throughout the Givetian, or that deltaic settings may have offered enough heterogeneity to support phacopids in a predominantly sandy setting. The connection between eye reduction in phacopids and variation in their palaeohabitat has been investigated very thoroughly (e.g., Crônier et al 2004, Feist et al 2009), but limited work has been done on the distribution of large-eyed phacopids like Pedinopariops, because the presence of large eyes is not exclusive to shallow water habitats. Chlupáč (1977) detailed a reduced diversity and abundance of phacopids from shallow water reefal assemblages and biostromes, and commented on the dominance of largeeyed phacopids in shallow water settings.…”

New Late Devonian phacopid trilobites from Marhouma, SW Algerian Sahara

“…-Frasnian phacopids with forwardly shifted small eye-lobes were questionably assigned to Houseops (Feist et al, 2009). These are now reassigned to the new genus mainly on account of the shorter, rather wide-based anterior glabella and the different configuration of the eye-lobe that is generally shorter, and has a deeper, outwardly concave palpebral furrow.…”