The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda. (15th August 2012)

• Record Type: Journal Article
• Authors: Ortega‐Hernández, Javier; Legg, David A.; Braddy, Simon J.
• Is Part Of: Cladistics. Volume 29:Number 1(2013:Feb.)
• Page Start: 15
• Page End: 45
• Publication Date: 2012-08-15
• Subjects: Cladistic analysis -- Periodicals; 578.012
• DOI: 10.1111/j.1096-0031.2012.00413.x
• Languages: English
• ISSNs: 0748-3007

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The phylogenetic position of aglaspidids, a problematic group of Lower Palaeozoic arthropods of undetermined affinities, is re‐examined in the context of the major Cambrian and Ordovician lamellipedian arthropod groups. A cladistic analysis of ten genera of aglaspidids <italic>sensu stricto</italic>, six aglaspidid‐like arthropods and 42 Palaeozoic arthropod taxa indicates that Xenopoda, Cheloniellida, Aglaspidida <italic>sensu lato</italic> and Trilobitomorpha form a clade (Artiopoda <xref ref-type="link" rid="b71">Hou and Bergström, 1997</xref>) nested within the mandibulate stem‐lineage, thus discarding previous interpretations of these taxa as part 'of the chelicerate stem‐group (Arachnomorpha <xref ref-type="link" rid="b65">Heider, 1913</xref>). The results confirm an aglaspidid identity for several recently described arthropods, including <italic>Quasimodaspis brentsae</italic>, <italic>Tremaglaspis unite</italic>, <italic>Chlupacaris dubia</italic>, <italic>Australaglaspis stonyensis</italic> and an unnamed Ordovician Chinese arthropod. The problematic Bohemian arthropod <italic>Kodymirus vagans</italic> was recovered as sister taxon to <italic>Beckwithia typa</italic>, and both form a small clade that falls outside Aglaspidida <italic>sensu stricto</italic>, thus discarding eurypterid affinities for the former. The analysis does not support the phylogenetic position of <italic>Kwanyinaspis maotianshanensis</italic> at the base of Conciliterga as proposed in recent studies, but rather occupies a basal position within Aglaspidida <italic>sensu lato.</italic> The results indicate a close association of aglaspidid arthropods with xenopods (i.e. <italic>Emeraldella</italic> and <italic>Sidneyia</italic>) and cheloniellids (e.g. <italic>Cheloniellon</italic>, <italic>Duslia</italic>); the new clade "Vicissicaudata" is proposed to encompass these arthropods, which are characterized by a differentiated posterior region. The phylogenetic position of aglaspidid arthropods makes them good outgroup candidates for analysing the internal relationships within the groups that form Trilobitomorpha. This work provides a much clearer picture of the phylogenetic relationships among Lower Palaeozoic lamellipedians.</p> </abstract>