Revision and subdivision of the polyphyletic ‘Leonaspis’ (Trilobita)

Abstract

ABSTRACTA phylogenetic analysis is performed on all species previously assigned to the odontopleurid trilobite genusLeonaspis. The PAUP analysis shows this genus, as conventionally defined, to be polyphyletic, composed of four groups of equal taxonomie rank.Leonaspis(s.s.) is here restricted to one of these groups only, a monophyletic set of species characterised by ‘four-spined’ pygidia (i.e. with four spines between the major border spines) and a thorax of nine segments.Kettneraspisis recognised for the largest of these four groups, and is composed of ‘two-spined’ species with nine thoracic segments.LeonaspisandKettneraspisbelong to the Odontopleurinae. A third group of previous ‘Leonaspis’ species constitute a new genus of the Acidaspidinae. Its species are characterised by being ‘four-spined’ and having ten thoracic segments. For these the new genusExallaspisis erected, with type speciesE. bufo. A fourth group of ‘Leonaspis’ species, being ‘four-spined’ with nine thoracic segments, belongs toEoleonaspis, an Ordovician odontopleurine genus.LeonaspisandExallaspisare temporally and spatially non-overlapping,Leonaspisbeing exclusively Gondwanan post-Wenlock, whereasExallaspisis restricted to areas north of the Rheic Ocean and ranges from basal Llandovery to Ludlow.Kettneraspisis pandemic. The condition of five epiborder spines and ten border spines on the free cheek is proposed as plesiomorphic for odontopleurids, and the border spines are shown to originate as two separate rows with alternating spines. A shift in position of the facial suture is shown to transfer the genal spine from the cranidium to the free cheek inKettneraspismeraspides of degree 1 or 2, and the previously suggested co-occurrence of a fixigenal and librigenal spine in these stages is refuted. Earlier proposed dimorphism is rejected, and two mechanisms for reduction in the number of pygidial border spines are proposed.Kettneraspis reetaesp. nov. is described.