Post-Kellwasser event recovery and diversification of phacopid trilobites in the early Famennian (Late Devonian)


Authors: Feist R

Published in: Bulletin of Geosciences, volume 94, issue 1; pages: 1 - 22; Received 2 October 2018; Accepted in revised form 5 March 2019; Online 21 March 2019

Keywords: phacopid trilobites, Famennian, biostratigraphy, phylogeny, morphology, systematics,

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While no Frasnian phacopid genera are known to survive the terminal Frasnian Kellwasser extinction event, recovery of phacopids in the early Famennian is characterised by one of the highest origination rates of the clade. In this study species and subspecies currently known are updated with regard to their age distribution according to conodont-based bio-zonation. They occur in representative sites including Sessacker (Rhenish Slate Mountains), Wieda (Harz), McWhae Ridge (Canning Basin, Western Australia), Beni Abbes (Algerian Sahara) and Montagne Noire (Southern France). More than two-thirds of the taxa are reduced-eyed or blind, which might indicate adaptation to deep offshore habitats. A few taxa with Phacops-like kidney-shaped eyes with many lenses represent shallower environments in the photic zone. The fauna is characterised by different features of the ventral cephalic doublure due to the presence or absence of individualized anterior border, vincular furrow and postvincular doublure. Phyletic affiliation to Frasnian taxa remains difficult to assess until these are better known for their diversity in various habitats. Chlupacops may be a possible ancestor of taxa with cephalic anterior border such as Nephranops and Houseops, while Cryphops and Trimerocephalus may be rooted in Acuticryphops as previously thought. The systematic part is devoted to diagnoses and descriptions that are completed by new morphological criteria leading to some taxonomic re-assignments. The following taxa are new: Nephranops (Nephranops) angerae sp. nov., Nephranops (Maternia) occitanicus subgen. et sp. nov., Pulvinocephalus gen. nov., P. (Pulvinocephalus) steinachensis triangulus subgen. et subsp. nov., P. (Cryphopsides) ovatus subgen. et sp. nov., P. (?Cryphopsides) walliseri ?subgen. et sp. nov., Trifoliops septimanicus sp. nov., Struveops wiedaensis sp. nov.


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