Phylogeny of some Devonian trilobites and consequences for the systematics of Austerops (Phacopidae)

Abstract

A comprehensive phylogenetic hypothesis for Devonian phacopid trilobites of the genus Austerops has not previously been proposed. We carried out a cladistic analysis of the 13 species and subspecies assigned to Austerops, based on a data matrix of 63 characters. Two species of the morphologically very similar genus Chotecops, C. auspex and C. hoseri, and seven other close relatives (Reedops cephalotes hamlagdadianus, Boeckops stelcki, Morocops granulops, Paciphacops logani, Phacops latifrons, Phacops araw and Pedinopariops (Hypsipariops) vagabundus) were also included in the analysis in order to test their relationship with species of Austerops. Parsimony analyses using a heuristic method, with Calyptaulax callirachis and C. glabella as outgroup taxa, produced two most parsimonious trees of 341 steps. These trees are partly consistent with trees obtained from additional analyses performed with modified data sets (deletion of homoplastic characters, multistate characters, continuous characters carved into 5% increments, thoracic and pygidial characters, or taxa with numerous unknown characters). Results suggest that Austerops sp. B and A.? sp. D are close to Chotecops hoseri and C. auspex, and that these species constitute a monophyletic group. Austerops Austerops menchikoffi, A. speculator and A. punctatus are also a monophyletic group and reasonably constitute a sister group of that formed by the rest of Austerops and Chotecops sensu lato, while A. hottonensis seems phylogenetically distant from other representatives of Austerops. Chotecops including C. hoseri and C. auspex together with Austerops sp. B and A.? sp. D seem derived from A. legrandi. The relationship between Austerops and Chotecops remains partly unresolved but it seems likely that their recognition as separate taxa results in paraphyletic groups. The phylogenetic analysis suggests that the currently poorly known Austerops sp. B and A.? sp. D should be reassigned to Chotecops.